“We had our baby,” my brother phoned me one November day in 1967. “Wonderful. Boy or girl?” I said. “Boy. David. [Long sigh] He has some problems. He is scheduled for heart sur- gery tomorrow. Both eyes have thick cataracts. And more.” “Oh, no. I am so sorry.” “Don’t worry. It’s not genetic. Dot had rubella when he was an embryo. We didn’t tell you because the doctor wasn’t sure and we didn’t want to worry you. They found rubella virus in him. It’s not in my genes; it doesn’t affect you.” I was heartsick for my brother and his wife. But he was concerned about me, six months pregnant with our first child. The hormones of pregnancy increase fear and anxiety, but at that moment I was far more concerned about his baby than mine. My concerns were justified. Over the next four years, our child, Bethany, was fine, but David was not. I watched him slowly learn to chew, to walk, to hum, and finally, at age 4, to talk. Hundreds of special doctors, nurses, teachers, and neigh- bors helped him. Thousands of developmental scientists contributed indirectly by describing how children like David can learn. Four decades have passed since that first phone call. David—at right in the photograph, with his brothers Mike and Bill—is in his 40s. He told me: I am generally quite happy, but secretly a little happier lately, especially since November, because I have been consistently getting a pretty good vibrato when I am singing, not only by myself but also in congregational hymns in church. [He explained vibrato:] When a note bounces up and down within a quartertone either way of concert pitch, optimally between 5.5 and 8.2 times per second. As you see, David is knowledgeable as well as happy. He also has a wry sense of humor. When I complained that my writing wasn’t progressing as fast as I wished, David replied, “That sounds just like a certain fa- ther I know.” This was an acute observation: David’s dad and I live three thousand miles apart, but we share half our genes and most of childhood; we are similar in many ways. This chapter begins to describe the myriad influences on human life, including genes and experience. It introduces the science of development over the life span, defining domains, perspectives, methods, and ethics—all crucial for mastery of this subject. But always remember the goal: to enable David, Bethany, and all the other 6.9 billion people on Earth to fulfill their potential throughout their lives. David’s life continues to be amazing, filled with joys and sorrows. So is yours. This chapter, and those that follow, trace that reality. >>Defining Development The science of human development seeks to understand how and why people— all kinds of people, everywhere, of every age— change over time. Growth is multidi- rectional, multicontextual, multicultural, multidisciplinary, and plastic. These five terms will be explained soon, but first we delve deeper into the definition: how and why, all kinds of people, and change over time. Understanding How and Why Developmental study is a science that seeks to understand the changes that occur as people age (Bornstein & Lamb, 2005). It depends on theories, data, analysis, critical thinking, and sound methodology—like every other science. And like all scientists, developmentalists ask questions and seek answers, trying to ascertain “how and why”—that is, trying to discover the processes of development and the reasons for those processes. Science is needed because our lives depend on the answers. People disagree vehemently about how children should be raised; whether emerging adults should marry; when adults should divorce, or retire, or die. Such subjective opinions arise from emotions and upbringing, not necessarily from evidence. Scientists seek to progress from opinion to truth, from subjective to objective, from wishes to out- comes. “The empirical sciences will show us the way, the means, and the obstacles” in making life what we want it to be (Koops, 2003, p. 18). To say that something is empirical means it is based on data, on demonstra- tions, on facts. Empirical sciences enable people to live full lives. Without scien- tific conclusions and then applications, human life would be “solitary, poor, nasty, brutish, and short,” as Hobbes (1651/1997) wrote before the scientific revolution. The Scientific Method To avoid unexamined opinions and to rein in personal biases, scientists follow the five basic steps of the scientific method: 1. Begin with curiosity. On the basis of theory, prior research, or a personal obser- vation, pose a question. 2. Develop a hypothesis. Shape the question into a hypothesis, a specific predic- tion that can be tested. 3. Test the hypothesis. Design and conduct research to gather empirical evidence (data). 4. Draw conclusions. Use the evidence to support or refute the hypothesis. 5. Report the results. Share the data, conclusions, and alternative explanations. Developmentalists begin with curiosity and then seek facts, drawing conclusions only after careful research and analysis of data. Replication—the repetition of a study, using different participants—often becomes a sixth step, needed before the scientific community accepts conclusions. Although reliance on evidence isintended to eliminate bias, scientists realize that any single study may include unknown distortions; therefore replication, elaboration, and analysis by other sci- entists are needed. Thousands of studies reported in this book are examples of the scientific method. Here we present just one, to illustrate the method clearly. Every year until the mid-1990s, thousands of 2- to 4-month-olds died of sudden infant death syn- drome (SIDS, called “crib death” in North America and “cot death” in England), including 5,000 annually in the United States. They seemed healthy, went to sleep, and never woke up. As their parents mourned, scientists asked why (step 1) and developed numerous hypotheses (the cat? the quilt? natural honey? brain damage? spoiled milk?). For years, a scientist named Susan Beal chronicled every SIDS death in South Australia, seeking factors that increased the risk. She found several (maternal smoking, lambskin blankets) and noted eth- nic variations: Australian babies of Chinese descent died of SIDS less often than did other Australian babies. Genetic? Most experts thought so. But Beal also noticed that Chinese babies usually slept on their backs, contrary to the European custom. She hypothesized (step 2) that sleeping position might matter. Beal convinced a large group of Australian parents to put their infants to sleep on their backs (step 3). Very few of the babies died of SIDS. After several years, she had enough data to draw conclusions (step 4): Backsleeping infants survived more often. Her published reports (step 5) (Beal, 1988) caught the attention of scientists in the Netherlands, where pediatricians had told parents that babies should sleep on their stomachs. Two Dutch scientists (Engelberts & de Jong, 1990) rec- ommended back-sleeping; thousands of parents took heed. As a result, SIDS was reduced in Holland by 40 percent in one year, a stunning replication (step 6). Replication then occurred elsewhere. By 1994, a “Back to Sleep” campaign cut the SIDS rate dramatically, saving tens of thousands of young lives (Kinney & Thach, 2009; Mitchell, 2009). In the United States, 5,245 babies died of SIDS in 1984—but only 2,034 in 2005. In nation after nation, back-sleeping cut SIDS in half. Scientists are now working on that other half (Kinney & Thach, 2009; Mitchell, 2009). The Nature–Nurture Debate This example highlights a historic puzzle, often called the nature– nurture debate. Nature refers to the influence of the genes that people inherit. Nurture refers to environmental influences, beginning with the health and diet of the embryo’s mother and continuing lifelong, including family, school, culture, and society. The nature–nurture debate has many other names, among them heredity– environment, maturation–learning, nativist–empiricist. Under whatever name, the basic question is: How much of any characteristic, behavior, or emotion re- sults from genes and how much from experience? Note that the question is “how much,” not “which,” because both genes and the environment affect every charac- teristic. Nature always affects nurture, and then nurture affects nature. Indeed, some scientists think that the ongoing interaction between genes and experiences is so varied, explosive, and profound that even “how much” is an out- dated concept (Gottlieb, 2007; Meaney, 2010; Spencer et al., 2009). “How much” implies proportions, but many developmentalists believe that the dynamic interac- tion makes “how much” a misleading question. Critical and Sensitive Periods The fact that nature and nurture interact helps clarify another question: whether or not timing is crucial. Thanks to scientific inquiry, we have learned that there are both critical periods and sensitive periods in development. A critical period is a time when something must occur to ensure normal de- velopment. For example, genes normally program the human fetus to develop arms and legs, hands and feet, fingers and toes, each over a specific period between 28 and 54 days after conception. Tragically, between 1957 and 1961, thousands of newly pregnant women in 30 nations took thalidomide, an antinausea drug. This disrupted prenatal development: If a woman ingested thalidomide between day 28 and day 54, the limbs of her newborn were malformed or absent (Moore & Persaud, 2007). Specifics depended on the precise day she swallowed the drug; before or after the critical period, no harm occurred. For most of development, no critical period is evident, but a sensitive period, when a particular development occurs most easily, is common. One example is language, best learned early in life. If children do not master their first language between ages 1 and 3, they may do so later (hence this is not a critical period), but their grasp of grammar may be impaired. Similarly, childhood is a sensitive period for fluent pronunciation in a second or third language. As often occurs with development, a sweeping generalization (as in the preceding sentence) does not apply in every case. Accent-free speech usually must be learned in the sensitive period before adolescence, but some adults with exceptional nature and nurture (naturally adept at speech and then immersed in a new language) learn to speak a second language flawlessly (Birdsong, 2006; Herschensohn, 2007). Now consider a more complex example of nature and nurture. Genetic Vulnerability Some young people become violent, hurting others as well as themselves. Indeed, if a person is ever going to kill someone, he (or less often, she) is most likely to do so between ages 15 and 25. Sociologists, psychologists, and economists have found many factors that contribute to youth violence, including past child abuse and cur- rent circumstances. The violent delinquent is often a boy who was beaten in child- hood and who lives in a drug-filled, crowded neighborhood (Maas et al., 2008). Yet some such boys never become violent. A fourth discipline—biology—suggests why. One genetic variant oc- curs in the code for an enzyme (monoamine oxidase A, ab- breviated MAOA) that affects neurotransmitters (chemicals in the brain). This gene comes in two versions, producing people with lower or higher levels of that enzyme. Both versions are normal; about one-third have low MAOA. A famous developmental study began with virtually every child born in Dunedin, New Zealand, between April 1, 1972, and March 31, 1973. The children and their families were examined on dozens of measures from early childhood on, providing literally hundreds of published studies based on a wealth of data, including parental practices and variants of the MAOA gene. Researchers found that boys who were mis- treated by their parents were about twice as likely to be overly aggressive (to develop a conduct disorder, to be violent, to be antisocial, and eventually to be convicted of a violent crime) if, and only if, they had the low-MAOA gene instead of the highMAOA one (Caspi et al., 2002; see Figure 1.1). Does this mean that becoming violent is inevitable for those with less of that enzyme? No. As Figure 1.1 shows, if they were not maltreated, boys with the low-MAOA gene were more likely than those with the high-MAOA gene to become law-abiding, peaceable adults. Such re- sults were surprising at the time, but recently many other scientists have found genes, or circumstances, that predispose people to be either un- usually successful or unusually pathological (Belsky et al., 2007; Keri, 2009). Such vulnerability is now accepted, although many still debate the specifics. Replication of this exact study has been problematic. Many other studies also show that inherited risk influences later behavior, but the impact varies from one place and group of participants to another. Peo- ple are particularly vulnerable to some risks in certain developmental periods (e.g,, in infancy to malnutrition, in adolescence to drug abuse, and so on). Now consider a study of a very different population: African Ameri- can 11-year-olds in rural Georgia, the United States (Brody et al., 2009). Parents and children in some families were taught to develop racial pride, family encouragement, honest communication, and house rules. Teenagers from this study who had a genetic risk (in this case, the short version of the 5HTTLPR gene) benefited from the special learning, en- gaging in relatively few risky behaviors. But those with the short gene and without family training often broke the law. (This study is further explained in Chapter 16.) Genetic Origins for Violent Crime Two variables— parental treatment and a variant of the gene that produces the enzyme MAOA—interact to affect the likelihood that a child will commit a violent crime. Of the boys in the “probable maltreatment” category, 10 percent were con- victed of a violent crime if their MAOA level was high, but 26 percent were convicted if their MAOA was low. FIGURE 1.1 Note that these examples involve nature and nurture. No period is either critical or sensitive unless a combination of maturation and ex- perience makes it so. Most of the time growth proceeds smoothly, and people develop hands, language, morals, and everything else that characterize our species. When things go awry, developmentalists look to both nature and nurture to understand the cause and the cure. Searching for cause and cure raises the issue of what science can and cannot do. Science cannot decide the purpose of life; we need philosophy or religion for that (National Academy of Sciences, 2008). Literature, film, and the other arts provide insights as well. As you will learn throughout this chapter, statistics, re- search methods, and ethics have both scientific validity and notable limitations. Don’t idealize science, and don’t trash it—use it well. Including All Kinds of People As the second element of our definition indicates, developmental science studies all kinds of people—young and old; rich and poor; of every ethnicity, background, sexual orientation, culture, and nation. The challenge is to identify both universal- ities and differences and then to describe them in ways that simultaneously unify humanity and distinguish each individual. The danger is in drawing conclusions based on a limited group. Both the universal and the unique are evident in everyone. For example, your father’s father was once a boy who never sent a text message, was not vaccinated against chicken pox, and did not fear nuclear war. That much is universal, useful for understanding almost every grandfather. Also universal is the fact that his val- ues and actions affect all of his descendents by his nature (you have one-eighth of his genes, and if you are male, his Y chromosome) and his nurture (his absence or presence affected your parents’ lives as well as your own). Yet he is (or was) unique. No one exactly like him will ever live again. His effect on you depends on dozens of other factors, involving both genes and culture. For example, some people, genetically, are inclined to rebel against tradition while others cling to it; some people, culturally, revere their ancestors and others, as one Italian immigrant quipped, become “American by learning how to be ashamed of our parents” (Leonard Covello, quoted in Kasinitz et al., 2008, p. 10). As you learn more about the life span, you will recog- nize the influence of hundreds of people and circumstances on your personality, thoughts, and decisions. Not every difference between one developing per- son and the norm is a deficit, as people once thought. By studying all kinds of people, of every age and background, developmentalists have come to appreciate the diversity of humankind, instead of assuming that someone unusual is to be pitied or changed. Some differences are welcome di- versities, not deficits. For instance, by age 75, 96 percent of all U.S. residents have married at least once in their lives (U.S. Bureau of the Census, 2009). Some of them thought being single was deficient, as the term old maid implied. However, research now finds that difference (in this case, not marrying) is not necessarily a deficit. When “all kinds of people” include some who avoid marriage and some in same-sex partnerships, we find that some of those people are happy, successful, and accomplished just as they are. This does not mean that everyone unmarried is happy or that all variations are benign, but it does mean that judgments about deviations should be made carefully, based on evi- dence, not opinion. Observing Changes over Time The third crucial element in the definition of developmental science is that indi- viduals change over time. Continuity and discontinuity, consistencies and transformations, from conception until death—these are our focus. Age is significant. Is it normal for a boy to throw himself down, kicking and screaming, when he is frustrated? Yes, if he is 2 years old; no, if he is 12. Is it normal for adults to plan their funeral? Yes at 90, no at 19. Every aspect of development interacts with every other; every person interacts with other people; all conditions and experiences interact continuously over time, each affecting the other. Consequently, scientists now envision development as the result of dynamic systems. The word systems captures the idea that a change in one aspect of a person, or family, or society affects all the other aspects because each part is connected to all the other parts (Thelen & Smith, 2006). The body is a system, or actually many systems (cardiovascular, respiratory, reproductive, and so on); a family is a system; so are neighborhoods, cities, nations, the world. Each part of development in each person is connected to many other parts of the system, and thus each part is affected by changes in other parts as time goes on. To pick a simple example, a birth turns a woman into a mother and a man into a father, a dramatic transformation of the individuals and the family system, and then other changes—in habits, goals, sleep, and so on—occur. This approach to development is “relatively new” for social scientists, but all of nature is dynamic. . . . seasons change in ordered measure, clouds assemble and disperse, trees grow to certain shape and size, snowflakes form and melt, minute plants and ani- mals pass through elaborate life cycles that are invisible to us, and social groups come together and disband. [Thelen & Smith, 2006, p. 271] Since change is the nature of things, it is not surprising that the study of human development itself has changed. Fifty years ago, scholars concentrated on chil- dren, who were thought to grow until age 18 or so, when change stopped. A few researchers focused on the “sad ending” of life and none on the “empty middle” (Bronfenbrenner, 1974). Then an insightful book around thirty years ago recognized that children affect adults just as adults affect children (Bell & Harper, 1977). And now with the dynamic-systems perspective, it is apparent that adults as well as children are con- tinually affected by one another and by life circumstances. No one is the same at age 35 and age 45, or even 35 and 36. Every day is new; every age is open to change. Consequently, the science of development must encompass the entire life span. With that insight, the life-span perspective has emerged; it is described in the next section. SUMMING UP Developmental study is a science, which makes it useful in discovering and validating facts. All sciences follow the scientific method, beginning with questions to answer and drawing conclusions after empirical research. Developing persons of every age, culture, and background teach us what is universal as well as what is unique. Some pe- riods of life are critical or sensitive periods for certain developmental changes, yet the interaction between nature and nurture is always evident. Differences among people are not necessarily deficits, although some people mistakenly assume that their own path is best for everyone. Change is systematic, ongoing, and dynamic throughout the entire life span. >>The Life-Span Perspective The life-span perspective, as set forth by Paul and Margret Baltes and their associates (Baltes et al., 2006; Staudinger & Lindenberger, 2003), views human development as (1) multidirectional, (2) multicontextual, (3) multicultural, (4) multidisciplinary, and (5) plastic. Each of these characteristics includes implica- tions that need to be described. Development Is Multidirectional Change is apparent in each aspect of life and in every direction. Over time, human characteristics change in multiple ways—increasing, decreasing, or hold- ing steady; in a line (linear), a curve (curvilinear), or up and down (zigzag). The curvilinear trajectory is the most difficult to capture statistically, but many things (from visual acuity to knowledge of calculus) advance and then decline over the life span. The dynamic variability of change is contrary to the traditional idea that development advanced bit by bit until about age 18, was stable until about age 50, and then declined. Sometimes discontinuity is evident when a rapid shift occurs, as happens at puberty when a child’s body becomes that of a woman or a man. Sometimes con- tinuity is found: From age 2 to age 10, children ordinarily gain a few pounds each year. Some things do not change: Each person is born and dies with about 20,000 genes, present in his or her body cells lifelong. Thus, many directions are possible; specifics vary. Many people believe that development occurs in stages, like a set of steps on a stairway (up, stable, up, stable, up, stable . . .). As you will read in Chapter 2, several major theorists—including Freud, Erikson, and Piaget—describe agerelated stages. Others—including Skinner and Maslow—do not. Research shows that some shifts seem stagelike (when one development trig- gers several others) and other shifts are gradual. From a life-span perspective, a multidirectional view allows us to understand when, how, and whether stages occur. A multidirectional perspective enables researchers to recognize that gains and losses often occur simultane- ously: Losses can lead to gains and vice versa (Baltes et al., 2006). Every change— going to college, getting mar- ried or divorced, moving to another neighborhood, the death of a parent—produces unexpected advances and retreats. Consider an example. When a man’s wife dies, his physical, intellectual, and social well-being often decline (van den Brink et al., 2004). One study found that, in the month after the death of a spouse, widowers entered nursing homes three times more often than did other men of similar age, education, and health (Nihtilä & Martikainen, 2008). That is one pattern, when the direction of every aspect of life seems downward. But the life-span perspective examines variations as well as averages, avoiding simple generalizations. Decline is common among widowers, but not inevitable. Some men expand their social worlds after mourning, and that triggers movement in other directions. A widower may develop new friendships, while income, intel- lectual stimulation, and nutrition may zigzag. Trends and trajectories sometimes follow unexpected paths. Development Is Multicontextual The second insight from the lifespan perspective is that development is multi- contextual, occurring in many contexts, including physical surroundings (climate, noise, population density, etc.) and family constellations. The impact of various physical and social environments is explained throughout this book. The need to consider many contexts was first emphasized by Urie Bronfenbrenner, who recommended an ecological-systems approach to developmental study (1977). He argued that developmentalists need to examine the systems that sur- round each person just as a naturalist examines the ecology, or the interrelationship, of each organism and its environment. Toward the end of his life, Bronfenbrenner renamed his theory bioecological (Bronfenbrenner & Morris, 2006) to ensure that its name reflected the natural settings and biological processes that the theory includes. Bronfenbrenner described three nested levels that affect each person (dia- grammed in Figure 1.2): microsystems (elements of the immediate surroundings, such as family and friends, school and religious classes), exosystems (local insti- tutions such as school system, religious organization, and workplace), and mac- rosystems (the larger contexts, including cultural values, economic policies, and political processes). Appreciating the dynamic interaction among the microsystem, the exosystem, and the macrosystem, Bronfenbrenner named a fourth system, the mesosystem, which connects the other systems. One example of a mesosystem is the interface between employment and family. Some mesosystems between work and home are obvious, such as family-leave policies and overtime schedules. Some are indirect, originating in the macrosystem, such as unemployment rates, mini- mum-wage standards, and male–female hiring practices. Finally, recognizing the importance of historical conditions, Bronfenbrenner described the chronosystem (literally, “time system”), which affects the other systems. Following through on Bronfenbrenner’s pioneering work, developmentalists take many contexts into account. Two of them are highlighted here because they are pervasive yet sometimes ignored: the historical and the socioeconomic contexts. The Historical Context All persons born within a few years of one another are said to be a cohort, a group who travel through life together, experiencing similar circumstances. Members of each cohort are affected by the values, events, technologies, and culture of their era. For example, political opinions lifelong are particularly influenced by events in emerging adulthood. Consequently, attitudes about war differ for the U.S. co- horts who came of age during World War II, the Cold War, or the conflicts in Vietnam, the Persian Gulf, Iraq, and Afghanistan. Sometimes demographic characteristics rather than headline-making events shape the historical context. For example, the cohort born between 1946 and 1964 is called the baby-boom generation because of a marked spike in the birth rate. The older members of that cohort are now beginning late adulthood, and their experiences are unlike those of their parents. One reason is the size of their co- hort, making them a large voting bloc that shapes policies regarding retirement and health care. If you doubt that national trends and events touch individuals, consider your first name—a word chosen especially for you. Look at Table 1.1, which lists the most popular names for boys and girls born into cohorts 20 years apart, beginning in 1928. Your name and your reaction to it are influenced by the era. The Socioeconomic Context Another context of development is the socioeconomic one, reflected in a person’s socioeconomic status, abbreviated SES, sometimes called social class (as in middle class or working class). SES reflects more than income: Education is often crucial. SES brings advantages and disadvantages, opportunities and limitations—all affecting housing, nutrition, knowledge, and habits. Although low income obvi- ously limits a person, other SES factors can make poverty better or worse. Even income is not a straightforward indication of poverty: Financial assets over a long period affect children’s learning more than their parents’ current income does (Yeung & Conley, 2008). A question for developmentalists: When does low SES do most damage? In infancy, poverty may mean inferior medical care and malnutrition, stunting the brain; in adulthood, job and marriage prospects are reduced as SES falls; in late adulthood, the accumulation of past stresses (including low SES) can overwhelm the body’s reserves, causing disease and death. Which is worse? The answer is not clear; SES is powerful at every age. Development Is Multicultural When social scientists use the term culture, they refer to a “meaning and informa- tion system, shared by a group and transmitted across generations, that allows the with a North American supermarket. group to meet basic needs of survival . . . pursue happiness and well- being, and derive meaning from life” (Matsumoto, 2009, p. 5). Citizens of a nation, residents of a region within a nation, members of an ethnic group, people living in one neighborhood, or even students in a college class can have their own culture, in that they have their own method of gathering information and ascribing meaning, or value, to life. Culture affects every action—indeed, every thought. Learning Within a Culture Russian developmentalist Lev Vygotsky (1896–1934) was a leader in describing the interaction between culture and education. He noted that each community in his native Russia (which included Asians and Europeans, of many faiths and languages) taught their children what- ever beliefs and habits their culture valued. As discussed in more detail in Chapters 2 and 9, Vygotsky developed the concept of guided participation, in which entire societies teach nov- ices the skills and habits expected within the particular culture. Guided participation often happens informally through “mutual involvement in several widespread cultural practices with great importance for learn- ing: narratives, routines, and play” (Rogoff, 2003, p. 285). That we are unaware of the culture we transmit is evident from a study of Chinese and U.S. parents of 20-month-olds. Parents in both cultures have small families and devote time and effort to their children’s language development. Book reading is common. In all of this, cultural similarities are apparent. However, researchers designed a picture book (no words)— with half the pictures from U.S. picture books and half from Chinese ones—and asked the parents to look at the book with their toddlers. Everything said was recorded and analyzed. The U.S. mothers used more nouns than verbs, and the opposite was true for the Chinese mothers. For example, at a picture of a dandelion, the U.S. mothers pointed out the petals, leaves, and stem, while the Chinese mothers noted that a dandelion could be picked or smelled (Brody et al., 2009). That difference re- flects the cultures of the United States and China. Ethnicity, Race, and Culture Confusion arises whenever people—scientists or nonscientists— refer to ethnic groups, races, and cultures. Each of these terms has a distinct meaning: The following definitions may help. People of an ethnic group share certain attributes, almost always including ancestral heritage and usually national origin, religion, and language (Whitfield & McClearn, 2005). Ethnic group is not the same as cultural group: some people of a particular ethnicity may not share a culture, and some cultures are followed by people of several ethnic groups. The term race has been used to categorize people on the basis of biology, particularly as it affects outward appearance. However, appearance is not a reliable indicator of biology, genetics, or development (Race, Ethnicity, and Genetics Working Group, 2005). Skin color (often used as a racial marker) is particularly misleading, since dark-skinned people whose ancestors were African are even more genetically diverse than light-skinned people whose ancestors were European (Tishkoff & Kidd, 2004). As one team of psycholo- gists expressed it, “Race is a social construction wherein individuals [who are] labeled as being of different races on the basis of physical characteristics are often treated as though they belong to biologically defined groups” (Goldston et al., 2008, p. 14). Unlike genetic differences, social constructions (ideas cre- ated by a society) can change (Rothenberg, 2007). Most social scientists agree that “the idea of race distorts, exaggerates, and maximizes human differences” (Smedley & Smedley, 2005, p. 22). Social constructions have power, given by people, not biology. Perceived racial differences can lead to discrimination, which can cause physical and psychologi- cal illness. Indeed, even when discrimination is not evident, each person’s racial self-concept affects his or her cognition (see the discussion of stereotype threat in Chapter 18). Some data in official documents (such as the U.S. Census), in research reports, and therefore in this book differentiate people by African, European, Hispanic, and Asian ancestry, sometimes thought to be races. When you encounter such data, remember that race may be misleading and that, although ethnicity, culture, and SES may overlap, “membership in an ethnic minority group is not equivalent to a common cultural experience,” as developmentalist Vonnie McLoyd explains (2006, p. 1145). Development Is Multidisciplinary Scientists often specialize, studying one phenomenon in one species within one domain at one age, using the methods and strategies of their particular discipline. For example, laboratory experiments with genetically altered mice are more likely reported by biologists than by sociologists; psychologists are intrigued by the de- velopment of various types of memory, and they experiment with nonsense words in order to understand it; anthropologists are fascinated by various forms of family life and rely on scientific observation “in the field” to learn more. All recognize, however, that human development over the life span is such a vast subject that insight and information from diverse disciplines are required to understand it. As a team of psychologists explain: “An integrative life-span devel- opmental framework [involves] interdisciplinary collaborations and multiple meth- odological approaches for understanding how and why individuals change” (Hofer & Piccinin, 2010, p. 269). To make it easier to study, development is usually segmented into three do- mains—biological, cognitive, and social—each one the specialty of scientists in a particular discipline. Development is also segmented into discrete age divisions, such as childhood, adolescence, and adulthood, each with approximate ages (see Table 1.2). Domains and age periods may be further divided. For example, some scholars study hormonal, moral, or emotional development, each of which is primarily (but not exclusively) within one of the domains (respectively, biological, cognitive, and social). Similarly, the life span can be divided into three periods, or seven (as in this text), or many more. For example, there is intriguing research on vision in the first weeks of life (newborns have particular trouble seeing contrasts, as well as the color pink) (Brown & Lindsey, 2009; Franklin et al., 2008); on the rela- tionship between intellectual ability and grip strength in the “oldest old”—one of three age stages within late adulthood (Takata et al., 2008); and on the sequence of self-assessed appearance, self-esteem, and dieting (all three domains) during the first few years of adolescence. Weaving together all these multidisciplinary and multiage strands reveals the pattern of human life. Of course, words and pages follow in linear succession and the brain thinks one idea at a time: It is impossible to consider all ages and domains simultaneously. All developmental scholars use discrete ages and topics to organize and focus their work, but here is the underlying truth: Although life is studied by domain and age, each domain and each stage affect the others. For example, your ability to learn from the paragraph you just read depends on your current maturity (a child wouldn’t grasp it) and all three domains: your physical state (hunger, sleep, temperature, and so on), mental ability (familiar words), and social influences (cultural values, people around you). Furthermore, your past education and an- ticipated future affect your current motivation: Only a multidisciplinary approach can begin to encompass all that. Two relatively new disciplines, genetics and neuroscience, have already affected our understanding of every age and aspect of development, as you will see now and in every chapter of this book. Development Is Plastic The term plasticity denotes two complementary aspects of development: Human traits can be molded (as plastic can be), yet people maintain a certain durability of identity (as plastic does). The concept of plasticity in development provides both hope and realism—hope because change is possible and realism because develop- ment builds on what has come before. Even the brain is plastic (Stiles, 2008). Part of the normal brain is dedicated to balance; we don’t fall down when we stand up, run, or even hop on one foot. How- ever, this part of the brain was destroyed (by an overdose of a prescription drug) in a woman named Cheryl. An observer wrote: First her head wobbles and tilts to one side, and her arms reach out to try to sta- bilize her stand. Soon her whole body is moving chaotically back and forth, and she looks like a person walking a tightrope in the frantic seesaw moment before losing his balance—except that both her feet are firmly planted on the ground. [Doidge, 2007, p. 1] A few neuroscientists, hoping that plasticity would allow recovery, tried to repro- gram Cheryl’s brain. They succeeded. Although the balance area in her brain remains dead, another part of her brain took over, and Cheryl now stands steady. This has implications for learning disabilities, for depression, for prejudice, for stroke victims, and for much more, as “[we] are all born with a far more adaptable, all-purpose, opportunistic brain than we have understood” (p. 26). Yet caution is stressed again here; plasticity does not mean that anything is possible, just that change may occur—for better or worse. Plasticity and David’s Future In some ways, plasticity underlies the other four characteristics of development. My nephew David, whose story opened this chapter, required heart surgery two days after he was born and again at age 5. His first eye surgery, at 6 months, destroyed one eye. As he grew older, malformations of his thumbs, ankles, feet, teeth, spine, and brain became evident. Predictions were dire: Some people won- dered why his parents did not place him in an institution. As a young child, David was severely retarded. Time and time again, experts from many disciplines nurtured David’s abilities. For example, at 9 months he did not crawl because his parents kept him safe intheir arms. Fortunately, a consultant from the Kentucky School for the Blind put him on a large rug, so he learned to feel the boundaries and crawl safely. Later he attended three specialized preschools, then a mainstreamed public school, then a special high school, then the University of Louisville—each with educators guided by research on learning. Surgical advances kept his heart beating, allowed his remaining eye to see, caused his jaw to realign, and improved his life in many other ways that would not have been tried by doctors a few decades earlier. As I have watched David’s development, plasticity is evident. Remember, plas- ticity cannot erase genetic endowment, childhood experiences, or permanent damage. David’s disabilities are always with him (he still lives at home). But by age 10, David had skipped a year of school and was a fifthgrader, reading at the eleventh-grade level. He learned languages (German and Russian, with some Spanish and Korean). In young adulthood, after one failing semester, he earned several As and graduated from college. David now works as a translator of German texts, which he enjoys because “I like providing a service to scholars, giving them access to something they would otherwise not have.” As his aunt, I have seen him repeatedly defy pessimistic pre- dictions. All five of the characteristics of the life-span perspective are evident, summarized in Table 1.3. Five Characteristics of Development Characteristic Multidirectional. Change occurs in every direction, not always in a straight line. Gains and losses, predictable growth, and unexpected transformations are evident. Multidisciplinary. Numerous academic fields—especially psychology, biology, education, and sociology, but also neuroscience, economics, religion, anthropology, history, medicine, genetics, and many more—contribute insights. Multicontextual. Human lives are embedded in many contexts, including historical conditions, economic constraints, and family patterns. Multicultural. Many cultures—not just between nations but also within them—affect how people develop. Plasticity. Every individual, and every trait within each individual, can be altered at any point in the life span. Change is ongoing, although neither random nor easy. Application in David’s Story David’s development seemed static (or even regressive, as when early surgery destroyed one eye) but then accelerated each time he entered a new school or college. Two disciplines were particularly critical: medicine (David would have died without advances in surgery on newborns) and education (special educators guided him and his parents many times). The high SES of David’s family made it possible for him to receive daily medical and educational care. His two older brothers protected him. Appalachia, where David and his family lived, has a particular culture, including acceptance of people with disabilities and willingness to help families in need. Those aspects of that culture benefited David and his family. David’s measured IQ changed from about 40 (severely mentally retarded) to about 130 (far above average), and his physical disabilities became less crippling as he matured. SUMMING UP Development is multidirectional, with gains and losses evident at every stage and in every domain. All the dimensions of development are affected, sometimes in opposite ways, by human experience. Among the many contexts of development are historical circumstances and economic conditions. A person’s life is affected partly by income and education, which encourage or restrict opportunity. Culture always shapes devel- opment, and it should not be confused with ethnicity or race. Each discipline uses par- ticular methodology to focus on one aspect of life; consequently, a multidisciplinary approach is needed to study the entire life span. Development is plastic: Both the brain and experience are connected to prior events and open to change. >Using the Scientific Method Now we focus on the crux of the scientific method: design- ing research and analyzing evidence. Statistical measures often help scientists discover relationships between vari- ous aspects of the data. (Some statistical perspectives are presented in Table 1.4) Every research design, method, and statistical measure has strengths as well as weaknesses. You will notice that every chapter in this text includes a Research Design in which the design of a particular study is explained and critiqued, to help you see the variations that, together, provide evidence for what is known about development. Now we consider three major types of research and then discuss three ways in which research focuses on change over time. Observation We are all observers: As a scientific method, observation includes many techniques in order to be less subjective. Scientific observation requires the researcher to record behavior systematically and objectively. Observations often occur in a natu- ralistic setting (such as a home, school, or public place), where people are likely to behave as they usually do. Scientific observation can also occur in a laboratory, where scientists record how people react in various situations. Observation is the mainstay of anthropologists, who try to be unobtrusive when they observe a culture. Historians use observation when they pore over old records to gain insight. Even with meticulous practice so as to achieve objectivity, observation is limited: It cannot prove what causes people to do what they do. The Experiment The experiment is designed to establish what causes what. In the social sciences, experimenters typically impose a particular treatment on a group of volunteer par- ticipants or expose them to a specific condition. Then they record whether their behavior changes. In technical terms, the experimenters manipulate an independent variable, which is the imposed treatment or special condition (also called the experimental variable; a variable is anything that can vary). This independent variable may af- fect whatever they are studying, called the dependent variable (which depends on the independent variable). Thus, the independent variable is the new, special treatment; any change in the dependent variable is the result. The purpose of an experiment is to find out whether an independent vari- able affects the dependent variable. In a typical experiment (as diagrammed in Figure 1.3), at least two groups of participants are studied. One group is called the experimental group, which gets the particular treatment (the independent variable). The other group is the comparison group (also called a control group), which does not. The Survey A third research method is the survey. Information is collected from a large num- ber of people by interview, questionnaire, or some other means. The survey is a quick and direct way to obtain data. However, acquiring valid survey data is far more difficult than it appears. For example, elections would be easy to predict (never “too close to call”) if people voted as they said they would, if the undecided followed the trends, and if those who refused to tell or who were not asked were similar to those surveyed. But none of that is true: People lie or change their minds; those who never talk to strangers are unlike those who talk freely; those who are not surveyed are more likely to be at college, or in prison, or available only on cell phone—all of which makes them younger and less predictable than those surveyed. Good scientists correct for all this, but total accuracy is unattainable. Furthermore, survey answers are influenced by the wording and the sequence of the questions, as well as by selective memory. For example, every year since 1991, thousands of high school students throughout the United States have been asked if they had sexual intercourse before age 13. Every year, about twice as many ninth-graders (14 percent in 2007) as twelfth-graders (7 percent) say yes. How could that be? Do twelfth-graders forget, do ninth-graders lie, or do sexually active ninth-graders drop out of school? Surveys, involving more than 200,000 students over the years, cannot tell. Studying Development over the Life Span Social scientists from every discipline use these three methods (observations, ex- periments, and surveys) to explore human behavior. In addition, for developmental- ists time is pivotal. To study change over time, researchers use one of three basic research designs: crosssectional, longitudinal, or cross-sequential (see Figure 1.4 on page 24). Cross-Sectional Research The most convenient (quickest and least expensive) way to study developmental change over time is with cross-sectional research. Groups of people of one age are compared with a similar group of people of another age. For instance, in the United States in 2008, 92 percent of men aged 35 to 44 but only 70 percent of those aged 55 to 64 were in the labor force (U.S. Bureau of the Census, 2010). Does this mean one out of every four men retires between age 40 and 60? Cross-sectional design might lead to that conclusion. However, might the groups differ in ways besides age? In this example, the younger U.S. men, on av- erage, had more education than the older ones. Perhaps education, not age, ac- counted for their higher official employment, while some less educated, older men worked off the books—the study cannot determine this. A related problem is that the number of people in a cohort affects the experi- ence of that cohort. Perhaps the 60year-old men, who were baby boomers, had more trouble finding work because there are so many of them. If so, a cohort effect might appear to be an age effect. Longitudinal Research To help discover whether age itself, not historical context, causes a developmental change, scientists undertake longitudinal research. This research design in- volves collecting data repeatedly on the same individuals as they age. Longitudinal research is particularly useful in studying development over many years (Elder & Shanahan, 2006; Hofer & Piccinin, 2010). You have already read about the links among the MAOA gene, child maltreat- ment, and adult criminality. That was among hundreds of findings from a longitu- dinal study of an entire cohort in New Zealand. Some other surprising findings of longitudinal research are given in Table 1.5. Developmentalists agree that longitu- dinal research is more accurate than crosssectional research. However, because so much effort and time are required, many longitudinal studies include far fewer participants than would be ideal, especially when developmentalists seek to study the interaction between several variables. The famous New Zealand study began with 1,037 participants, and only 13 boys were in the severely maltreated, low- MAOA group. Four of them were convicted of violent crimes as adults, as were 11 of the 42 “probably maltreated” low-MAOA boys. These are high proportions, but, as you see, low numbers. The New Zealand study was successful in following the arrest rate of most par- ticipants (since most stayed in New Zealand and the court records are excellent), but in most decades-long studies, some participants withdraw, move to an un- known address, or die. This skews the final results because those who disappear are unlike those who remain in the study. Another problem is that participants become aware of the questions or the goals of the study and therefore may change in ways that most other people do not. Probably the biggest problem in longitudinal research comes from the chang- ing historical context. Science, popular culture, and politics alter life experiences, and those changes limit the current relevance of data collected on people born decades ago. Results from longitudinal studies of people born in 1900, as they made their way through childhood, adulthood, and old age, may not be relevant to people born in 2000. Finally, the need to wait decades for conclusions from longitudinal research makes it difficult to apply findings to current problems. The connection between smoking in adolescence and lung cancer in late use adulthood took decades to prove. Currently, because of alarm about the possible harm caused by ingesting industrial compounds, called phthalates, from the plastic of baby bottles, many parents now glass baby bottles. Might the risk of occasional shattered glass hurt more people than chemicals in plastic? Longitudnal research will tell us—in a few decades. Cross-Sequential Research As you see, cross-sectional and longitudinal research each has advantages that compensate for the other’s disadvantages. Scientists have discovered a third strat- egy that involves using these two together, often with complex statistical anal- ysis (Hartmann & Pelzel, 2005). This combination is called cross-sequential research (also referred to as cohort-sequential or time-sequential research). With this design, researchers study several groups of people who are of different ages (a crosssectional approach) and follow them over the years (a longitudinal approach). A cross-sequential design lets researchers compare findings for a group of, say, 18-year-olds, with findings for the same individuals at age 8, as well as with findings for groups who were 18 a decade or two earlier (see Figure 1.4). Cross- sequential research thus allows scientists to disentangle differences related to chronological age from those related to historical period. One well-known cross-sequential study (the Seattle Longitudinal Study) found that some intellectual abilities—including the ability to build one’s vocabulary— increase throughout adulthood, whereas others— such as speed of thinking—start to decline at about age 30 (Schaie, 2005). This study also discovered that declines in math ability are related more closely to changes in school curricula than to age, a finding that neither cross-sectional nor longitudinal research alone could reveal. SUMMING UP Developmentalists use many research methods, each with advantages and disadvan- tages. Observational research requires careful and systematic recording of whatever actually occurs. Experiments seek to establish cause and effect, as revealed by change in the dependent variable. A true experiment compares at least two groups, similar in many ways except that one receives a particular treatment (the independent variable) that the other does not. Surveys are useful for large groups, but accuracy depends on factors not always evident. To study change over time, cross-sectional and longitudinal research are both useful, but a combination of the two, often called crosssequential, is best. ■ >>Cautions from Science The scientific method illuminates and illustrates human development as nothing else does. Facts, hypotheses, and possibilities have emerged that would not be known without science—and people of all ages are healthier and more capable because of it. For example, infectious diseases in children, illiteracy in adults, depression in late adulthood, and racism and sexism at every age are much less prevalent today than a century ago. The average life span in developed nations is about 80, not 50 as it was a century ago. Science contributed to all these changes; many of us would be dead without it. Developmental scientists have also discovered unexpected sources of harm. As detailed in later chapters, cigarettes, television, shift work, lead paint, video games, and even automobiles are less benign than people first thought. Although the benefits of science are many, so are the pitfalls. We now discuss three of them: misinterpreting correlation, relying exclusively on numbers, and ignoring ethics. Correlation and Causation Probably the most common mistake in interpreting data is to think that correla- tion means causation. It does not. A correlation exists between two variables if one variable is more (or less) likely to occur when the other does. A correlation is positive if both variables tend to increase together or decrease together, negative if one variable tends to increase while the other decreases, and zero if no connection is evident. To illustrate: From birth to age 9, there is a positive correlation between age and height (children grow taller as they grow older), a negative correlation between age and hours of sleep (children sleep less as they grow older), and zero correlation between age and number of toes (barring a rare accident or late-life diabetes, after the eighth prenatal week, humans have ten toes lifelong). (Now take the quiz on correlation in Table 1.6.) Expressed in statistics, correlations vary from +1 (the most positive) to −1 (the most negative). Totally positive or totally negative correlations are virtually never found: There are always exceptions that reduce the strength of the correlation. Indeed, a correlation of +0.3 or −0.3 is noteworthy; a correlation of +0.8 or −0.8 is amazingly high. Many correlations are unexpected. For instance, first-born children develop asthma more often than later-born children, teenage boys commit suicide more often than teenage girls, and immigrants have fewer low-birthweight babies than the native born within the same ethnic group. Now consider another example. In the United States, there is a positive correla- tion between a couple’s age at marriage and the length of the marriage: The older a newlywed couple, the more likely their marriage will last. Teenage brides are particularly divorce-prone. As one would expect from this correlation, if a place has many young marriages, that place will also have many divorces. Oklahoma and Massachusetts are examples. To be specific, the median age at first marriage in Oklahoma is 25, two years lower than the national average, and 10 percent of Oklahoma adults have divorced three (or more) times. The median marriage age in Massachusetts is 29; only 2 percent of adults have been divorced three times (American Community Survey, 2008). Does this mean that marrying young causes divorce? No. Remember the man- tra: Correlation is not causation. Perhaps a third variable, education, underlies the correlation between the other two. People who are college graduates marry later and divorce less, and Massachusetts has more such people than Oklahoma. Cohort and culture may be pivotal. In nineteenth-century America, the correla- tion was negative: Younger (not older) marriages tended be long-lasting. A negative correlation between age and length of marriage is also reported in some develop- ing nations. As this example shows, correlations are intriguing—but conclusions about causes may be wrong. Quantity and Quality A second caution concerns how heavily scientists rely on data produced by quan- titative research (from the word quantity, such as more or less, higher or lower, in rank order, in percents, or in numerical scores). Because quantitative research data fit neatly into categories and statistics, they can be easily translated across cultures and for diverse populations. One example of quantitative research is school test scores, used to measure the effectiveness of education, or to allow pro- motion, or to admit a high school student to college. Since quantities can be easily summarized, compared, charted, and replicated, many scientists prefer quantitative research. Statistics require numbers. Quan- titative data are said to provide “rigorous, empirically testable representations” (Nesselroade & Molenaar, 2003, p. 635). Without the test scores to measure achievement, students might be rejected by colleges because of their ethnicity, or religion, or income. However, when data are reduced to numbers, some nuances and individual distinctions are lost. Many developmental researchers thus turn to qualitative research (from quality)—asking open-ended questions, reporting answers in nar- rative (not numerical) form, and generating “a rich description of the phenomena of interest” (Hartmann & Pelzel, 2005, p. 163). Qualitative research reflects di- versity and complexity, but it is vulnerable to personal bias and hard to replicate. Particularly if one person, a single case study, is used, conclusions may be idiosyn- cratic. (In this chapter, I refer to one case, my nephew David. Is he an example of proven generalities, or is he atypical and thus misleading?) Quantitative research has serious drawbacks as well, especially for a dynamic- systems approach to the life span. Since each person is unique, and change is multidirectional and multicontextual, numbers may obscure individuality. The solution: a combination of quantitative and qualitative methods. Sometimes sci- entists translate qualitative research into quantifiable data; sometimes they use qualitative studies to suggest hypotheses for quantitative research. Ethics The most important caution for all scientists, especially for those studying humans, is to uphold ethical standards. Each academic discipline and professional society involved in the study of human development has a code of ethics (a set of moral principles). Most educational and medical institutions have an Institutional Review Board (IRB), a group that permits only research that follows certain guidelines. Although IRBs often slow down scientific study, some research conducted before they were established was clearly unethical, especially when the par- ticipants were children, members of minority groups, prisoners, or animals (Blum, 2002; Washington, 2006). Protection of Research Participants Central to every IRB is the attempt to ensure that participation in research is vol- untary, confidential, and harmless. In Western nations, this entails the informed consent of the participants—that is, their understanding of the research proce- dures and of any risks involved. If children are involved, consent must be obtained from the parents as well as the children, and the children must be allowed to stop at any time. In some other nations, ethical standards also require consent of the family and village elders (Doumbo, 2005). Protection of participants may conflict with the goals of science. The Cana- dian Psychological Association (2000) is quite explicit about such conflicts (see Table 1.7). Implications of Research Results Once a study has been completed, additional ethical issues arise. Scientists are obligated to “promote accuracy, honesty, and truthfulness” (American Psychologi- cal Association, 2002); that obligation precludes distorting results to support any political, economic, personal, or cultural position. Deliberate falsification is rare, but insidious dangers include unintentionally slanting the conclusions or withholding publication, especially when there is “fe- rocious . . . pressure from commercial funders to ignore good scientific practice” (Bateson, 2005, p. 645). Even nonprofit research groups and academic institutions may put undue pressure on scientists to produce publishable results. For this reason, scientific training, collaboration, and replication are essential. Numerous safeguards are built into scientific methodology, including the fact that reports in professional journals are typically “peer reviewed,” meaning that each article is evaluated by scientists not connected with the author(s) before it can be published. Reports also include (1) the researchers’ affiliations and sources of funding, (2) details for replication, (3) the limitations of the research, and (4) alternative interpretations. What Should We Study? Long before designing and publishing research, the first ethical question for every scientist is what research is needed to enable more humans to live satisfying and productive lives. Consider these questions, for instance: Do we know enough about prenatal drug abuse to protect every fetus? ■ Do we know enough about poverty to enable everyone to be healthy? ■ Do we know enough about sex to eliminate AIDS, unwanted pregnancy, and sexual abuse? ■ Do we know enough about dying to enable everyone to die with dignity? The answer to all these questions is a resounding NO. The reasons are many, but a major one is that these topics are controversial. Some researchers avoid them, fearing unwelcome and uninformed publicity (Kempner et al., 2005). Few funders eagerly support scientific studies of drug abuse, poverty, sex, or death, partly because opinions on these subjects may conflict with the facts. Yet devel- opmentalists have an obligation to study whatever helps the human family. Many people suffer because questions go unanswered—or even unasked. The next cohort of developmental scientists will build on what is known, mind- ful of what needs to be understood. Remember the goal: to help the Earth’s 6.9 billion people. Much more needs to be learned. The next 25 chapters are only the beginning. SUMMING UP Science has helped people in many ways over the past century. However, there are several potential pitfalls in scientific research. For instance, correlations are useful, but they may be mistakenly used to “prove” cause rather than simply indicate connection. Quantitative research is easier to analyze and compare, but qualitative research reveals more nuances. Scientists follow codes of ethics that require them to be respectful of research participants by getting their informed consent and protecting their confidenti- ality. Scientists must not let their opinions influence their research results as they study issues that are crucial for human development. SUMMARY Defining Development 1. The study of human development is a science that seeks to understand how people change or remain the same over time. As a science, it begins with questions and hypotheses, gathers empirical data, and reports results. 2. All kinds of people, of every age, culture, and background, are studied by developmental scientists. The goal is to help all people develop well, by finding the universal patterns of human growth and by recognizing that each person is unique. 3. A dynamic-systems approach emphasizes that change is ongo- ing, with each aspect of development affecting every other part. Children influence adults just as surely as adults guide children. Continuity and discontinuity, consistency and transformation are evident throughout the life span. The Life-Span Perspective 4. The life-span approach recognizes that development is multidirectional, multicontextual, multicultural, multidisciplinary, and plastic. 5. Change is multidirectional: Both continuity (sameness) and discontinuity (sudden shifts) are evident, as are many other trajectories. 6. A multicontextual approach to development recognizes the power of ecological circumstances that surround each person. Historical contexts—events or innovations—shape people of each cohort, and socioeconomic status (SES) affects development lifelong. 7. The multicultural approach recognizes that culture promotes customs, values, and perceptions that guide human life. Culture is not the same as ethnicity; race is a social construction, not a biological one. 8. Understanding development over the life span requires research and insights from many academic disciplines. This multidisciplinary approach uses methods and investigates questions from each field, with discoveries from neuroscience recently reverberating in many other disciplines. 9. Human development is plastic, which means that individuals can be molded as time goes on by their circumstances, efforts, and unexpected events. Although change is always possible, ear- lier experiences and genetic tendencies influence people lifelong. Using the Scientific Method 10. Research methods include observation (to record what normally occurs), the experiment (to learn what causes what), and the survey (to assess many people quickly). Each method has strengths and weaknesses. 11. To study how people change as the days and years go by, scien- tists use three research designs: cross-sectional research (compar- ing people of different ages), longitudinal research (studying the same people repeatedly over time), and crosssequential research (combining longitudinal and cross-sectional methods). Cautions from Science 12. A correlation shows that two variables are related in some way. However, correlation is not causation: A connection between two variables can arise in many ways for many reasons. 13.Research can be quantitative (reported with numbers or quanitities) or qualitative (reported with words or narratives). Qualitative research captures the nuances of individual lives, but quantitative research is easier to replicate, interpret, and verify. Each complements the other. 14. Ethical behavior is crucial in all the sciences. Not only must participants be protected and their identities kept confidential, but results must be reported clearly and interpreted carefully. The most important ethical question is whether scientists conduct and analyze the research that is most critically needed to improve human development in all cultures, generations, and conditions. When I was little, on special occasions we drove to my grandparents’ farm, where my father grew up with his three brothers and one sister, all married with children. My mother sang, “Over the river and through the woods, to grandmother’s house we go.” When we arrived, my brother and I played with our twelve cousins, in- cluding three other girls my age. I remember turkey, mashed potatoes, and lemon meringue pie; horses and hay in the barn; grandma wearing an apron; grandpa resting his big hands over a huge coffee mug; and enormous wooden rocking chairs in the sitting room. But my strongest single memory is a bitter one: One time, Grandma gave us girls presents, precursors of Barbie dolls. Mine had a peach- colored gown; my cousin’s had a white bride’s dress and veil. Why did I feel rejected? Now I can think of many good reasons that particular cousin got the bride doll. But as a girl, my simple theory about presents and brides led to resentment. This chapter outlines five theories of human development, or actually ten, since each theory has several versions. There are hundreds more theories about the human life span, some explained later. Before beginning, however, you should know that theorizing is part of human nature. In fact, according to “theory theory,” young children spontaneously develop theories to explain whatever they observe, because that is what humans do (Gopnik & Schulz, 2007). My theory led me to believe that Grandma loved my cousin more than me. >>What Theories Do A developmental theory is a systematic statement of general principles that pro- vides a coherent framework for understanding how and why people change as they grow older. “Developmental theorists try to make sense out of observations . . . [and] construct a story of the human journey from infancy through childhood or adulthood” (Miller, 2011, p. 2). Such a story, or theory, connects facts and obser- vations with patterns and explanations, weaving the details of life into a meaning- ful whole. A developmental theory is more than a hunch or a hypothesis and is far more comprehensive than my simple theorizing about beautiful brides. The crucial aspect is that theories provide frameworks of understanding and thus are broader than the many observations from which they arise. As an analogy, imagine building a house. A person could have a heap of lumber, nails, and other materials, but without a plan and labor, the heap cannot become a building. Furthermore, not all houses are alike: People have theories about houses that lead to preferences for the number of stories, bedrooms, entrances, and so on. Likewise, the observations and empirical studies of human development are es- sential raw materials, but theories put them together. As Kurt Lewin (1943) once quipped, “Nothing is as practical as a good theory.” Theories differ; some are less comprehensive or adequate than others (why did we forget a back door?), and each is constructing a somewhat different home, but without theory, we have only a heap. Questions and Answers As we saw in Chapter 1, the science of human development begins with questions. Among the thousands of important questions are the following, each central to one 1. 2. 3. 4. 5. of the five theories described in this chapter: Do early experiences— of breast-feeding or attachment or neglect—linger into adulthood, even if they seem to be forgotten? Does learning depend on specific instruction, punishment, and examples? Do children develop moral principles, even if they are not taught right from wrong? Does culture guide behavior? Is that why Okinawa has more voters than Ohio? Is survival a human instinct, the bedrock value for all of us? Each of the five questions above is answered “yes” by one of the five major theo- ries—in order: question 1 by psychoanalytic theory, question 2 by behaviorism, question 3 by cognitive theory, question 4 by sociocultural theory, and question 5 by universalism. Each question is answered “no” or “not necessarily,” however, by several others. For every answer, more questions arise: Why or why not? When and how? And so what? This last question is crucial for the science of human development, because the implications and applications of the answers affect ev- eryone’s daily life. To be more specific about what theories do: ■ Theories produce hypotheses. ■ Theories generate discoveries. ■ Theories offer practical guidance. If a 5-year-old shouts “I hate you!” at his father, the man’s reaction (smiling, ignoring, spanking, or asking “Why?”) depends on his theory of development, whether or not he knows it. Then his wife’s reaction to him (perhaps approval or dismay, delivered with a kiss or a slap) depends on her theory of child rearing and marriage, again whether she knows it or not. Facts and Norms Do not confuse theories with facts. Theories raise questions, suggesting hypoth- eses that lead to research that gathers empirical data, which are facts that may lead to conclusions. Each of the theories soon to be explained has led to research, which has verified and refuted aspects of the theory and thereby moved the sci- ence of development forward. Thus, a theory is neither true nor false; it is provocative and useful, leading to insight and exploration. For example, some people dismiss Darwin’s theory of evolution as “just a theory,” while others believe it explains all of nature since the beginning of time. No to both. Good theories should neither be dismissed nor equated with facts. Instead, theories deepen thought; they are useful (like a house plan), leading to new interpretations, hypotheses, and perspectives. As already explained, developmental theories are comprehensive, detailed, and useful, unlike the simple theories of children or the implicit theories of customs. But those simpler theories make the distinction between theory and fact quite clear, so we return to the bride doll. My bitterness grew from a dominant theory when I was a child—that it was best for everyone to marry one person lifelong, have at least two children, and visit their parents, who should stay in their own house. That is what my grandparents’ children all did. They pitied my mother’s two unmarried sisters, Aunt Ida and Aunt Marie. Consequently, I fantasized about my wedding; I named my seven imagined children; I was happy when my Aunt Marie, about age 40, finally married. My theory was held by many in my culture, in which having more than one spouse was illegal (“bigamists” went to jail), divorce meant a “failed” marriage, “only” chil- dren had psychological problems, and if elders were “put away” in nursing homes, their relatives felt ashamed. As you see, emotions, assumptions, and laws followed from this commonly held theory. That theory of adulthood is no longer potent, as the “difference is not deficit” maxim in Chapter 1 explains. Research finds that many adults avoid marriage or parenthood but nonetheless seem happy. Indeed, some say that the pro-family the- ory I knew as a child has been replaced, at least in Western middle-class culture, by another untested theory—that personal happiness is the goal of life. That leads to another set of ideas—that unhappy spouses should divorce, childless marriages are fine, and older adults should not burden their offspring. Obviously, people agree or disagree with these theories. Scientists design stud- ies to investigate them because the theories themselves are not facts, and “each theory of developmental psychology always has a view of humans that reflects philosophical, economic, and political beliefs” (Miller, 2011, p. 17). Awareness of the possible bias within each theory helps in research, as the facts may make a sci- entist switch to another theory. You will see this as we explain various changes in developmental theories, but first let’s look at another common example that shows how quickly humans develop theories. People buy many makes and models of cars. They are influenced by facts, such as fuel efficiency and popularity. But they are also affected by their theories of life, quite apart from facts. Consider the Hummer, a vehicle “widely loathed” by some, who judge owners as “callous Earthkillers,” and loved by others, including one person who told the critics to “grow up and join us Americans that believe in our freedom. . . . Stop trying to oppress others that don’t share your beliefs, color, and religion” (quoted in Walker, 2009, p. 22). Callous? Oppression? Perhaps. But before you agree with either side, some research is needed. That’s why we need theories, to show us what studies might verify or dispute common assumptions about life. Theories give insight and guidance—especially when developmental problems occur: the misbehaving child, the drug-using adolescent, the risk-taking young adult, the angry parent, the disoriented older adult. Without theories, we would be merely reactive and bewildered, adrift and increasingly befuddled, blindly fol- lowing our culture and our prejudices. Unless we recognize that theories are useful, but in need of verification and exploration, we might be stuck with a limiting, inaccurate, or childish theory—as I was with the bride doll. SUMMING UP Theories provide a framework for organizing and understanding the thousands of observations and daily behaviors that occur in every aspect of development. Theories are not facts, but they powerfully affect thought and behavior, suggesting hypotheses and providing guidance. Thus, theories are practical—they frame and organize our millions of experiences, influencing the entire life span. >>Grand Theories In the first half of the twentieth century, two opposing theories— psychoanalytic theory and behaviorism (also called learning theory)—began as general theories of psychology. By midcentury, cognitive theory had emerged, becoming the domi- nant seedbed of research hypotheses. All three theories are “grand” in that they are comprehensive, enduring, and widely applied (McAdams & Pals, 2006). Psychoanalytic Theory Inner drives, deep motives, and unconscious needs rooted in childhood are the foundation of psychoanalytic theory. These basic underlying forces are thought to influence every aspect of thinking and behavior, from the smallest details of daily life to the crucial choices of a lifetime. Freud’s Ideas Psychoanalytic theory originated with Sigmund Freud (1856– 1939), an Austrian physician who treated patients suffering from mental illness. He listened to their accounts of dreams and fantasies and to their uncensored streams of thought, and he constructed an elaborate, multifaceted theory. According to Freud, development in the first six years occurs in three stages, each characterized by sexual interest and pleasure centered on a particular part of the body. In infancy, the erotic body part is the mouth (the oral stage); in early childhood, it is the anus (the anal stage); in the preschool years, it is the penis (the phallic stage), a source of pride and fear among boys and a reason for sadness and envy among girls. Two more developmental periods then follow early childhood. After the phallic stage, latency occurs and then, at puberty, the genital stage arrives, lasting throughout adulthood (Table 2.1 on the next page describes the stages in Freud’s theory). Freud maintained that at each stage, sensual satisfaction (from stimulation of the mouth, anus, or penis) is linked to major devel- opmental needs and challenges. During the oral stage, for example, sucking provides not only nourishment but also pleasure for the baby and attachment to the mother. Next, during the anal stage, pleasures that arise from control and self-control—initially with defecation and toilet training—are paramount. Freud called each stage psychosexual because children derive erotic pleasure from whatever body part is central at each stage. This idea (infantile sexuality) was one reason psychoanalytic theory was rejected at first. Among Freud’s most influential ideas was that each stage includes its own po- tential conflicts. Conflict occurs, for instance, when parents try to wean their ba- bies (oral stage) or teachers expect 6-year-olds to become independent of their parents (phallic stage). According to Freud, how people experience and resolve these conflicts—especially those related to weaning, toilet training, and sexual pleasure—determine personality patterns, because “the early stages provide the foundation for adult behavior” (Salkind, 2004, p. 125.) Freud did not believe that new stages occurred in the adult years; rather, he believed that adult personalities and habits were influenced by earlier stages. Unconscious conflicts rooted in a childhood stage may be evident in behavior—for instance, smoking cigarettes (oral) or keeping careful track of money (anal) or becoming romantically attracted to a much older partner (phallic). For all of us, psychoanalytic theory contends, childhood fantasies and memories remain powerful lifelong, particularly as they affect the sex drive (which Freud called the libido). If you have ever wondered why lov- ers call each other “baby” or why many people refer to their spouse as their “old lady” or “sugar daddy,” then Freud’s theory provides an explanation: The parent–child relationship is the model for all forms of intimacy. Many other aspects of psychoanalytic theory may explain adult behavior. According to Freud, the personality has three parts: the id (unconscious drives, inborn and animallike, mostly sexual and ag- gressive), the superego (the moral ideal, the conscience, learned from parents and society), and the ego (the conscious self). The id is domi- nant in infancy, the superego develops in the phallic stage, and by adulthood, a strong ego is able to defend itself against attacks from the id and superego. That defense occurs with defense mechanisms that keep the id and superego under control. Freud identified many defense mechanisms, some more effective than others. Two that are often used in adulthood are rationalization (finding a logical reason to justify something that actually springs from the irrational id or superego) and sublimation (transforming energy from the libido to create something acclaimed by others, such as a musical masterpiece). Erikson’s Ideas Many of Freud’s followers became famous theorists themselves. They acknowl- edged the importance of the unconscious and of early childhood experience, but each of them expanded and modified Freud’s ideas. Anna Freud (Sigmund’s daughter) and Carl Jung are mentioned later in this text. We turn now, though, to the most notable developmental theorist, Erik Erikson (1902– 1994). Erikson never knew his Danish father. He spent his childhood in Germany, his adolescence wandering through Italy, and his young adulthood in Austria, working with Freud. He married an American, fleeing to the United States just before World War II began. His experiences in many nations, as well as his studies of Harvard students, Boston children at play, and Sioux and Yurok Indians, led Er- ikson to stress cultural diversity, social change, and psychological crises through- out the life span. These elements are all present in Erikson’s massive psychoan- alytic study of Mahatma Gandhi, who was born in India, educated in Britain, and practiced law in South Africa. According to Erikson, those experiences forged Gandhi’s psychosocial identity, enabling him to lead the fight for In- dian independence (Erikson, 1969). Erikson described eight developmental stages, each characterized by a particular challenge, or developmental crisis (summarized in Table 2.1). Al- though Erikson named two polarities at each crisis, he recognized a wide range of outcomes between these opposites. For most people, development at each stage leads to neither extreme but to something in between. The resolution of each crisis depends on the interaction between the individual and the social environment. In the stage of initiative versus guilt, for example, children between ages 3 and 6 often want to undertake activities that exceed the limits set by their parents and culture. They jump into swimming pools, put their pants on backwards, mix cakes according to their own recipes, wander off alone. Such efforts to act in- dependently leave them open to feelings of pride or of failure, producing guilt if adults are too critical. As you can see from Table 2.1, Erik- son’s first five stages are closely related to Freud’s stages. Erikson, like Freud, believed that problems of adult life echo unresolved conflicts of childhood. For example, an adult who has diffi- culty establishing a secure, mutual relationship with a life partner may never have resolved the first crisis of early infancy, trust versus mistrust. Even in late adulthood, one older person may be outspoken while another fears saying the wrong thing, because they resolved their initiative-versus-guilt stage in opposite ways. In one crucial way, Erik- son’s stages differ significantly from Freud’s: They emphasize each person’s relationships to family and culture, not sexual urges. Behaviorism The second grand theory arose in opposition to the psychoanalytic notion of the unconscious. John B. Watson (1878–1958) argued that, if psychology was to be a true science, psychologists should examine only what they could see and measure: behavior, not irrational thoughts and hidden urges. In Watson’s words: Why don’t we make what we can observe the real field of psychology? Let us limit ourselves to things that can be observed, and formulate laws concerned only with those things. . . . We can observe behavior—what the organism does or says. [Watson, 1924/1998, p. 6] According to Watson, if psychologists focus on behavior, they will realize that ev- erything can be learned. He wrote: Give me a dozen healthy infants, well-formed, and my own specified world to bring them up in and I’ll guarantee to take any one at random and train him to become any type of specialist I might select—doctor, lawyer, artist, merchant chief, and yes, even beggar-man and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors. [Watson, 1924/1998, p. 82] Other psychologists, especially in the United States, agreed. They developed behaviorism to study actual behavior, objectively and scientifically. Behavior- ism is also called learning theory because it describes how people learn and de- velop habits, step by step. For every individual at every age, from newborn to centenarian, behaviorists describe laws detailing how simple actions and envi- ronmental responses shape complex competencies, such as reading a book or making a family dinner. Learning theorists believe that development occurs in small increments: A per- son learns to read, or cook, or anything else bit by bit over a long time. Because change is cumulative, behaviorists, unlike Freud and Erikson, describe no specific stages (Bijou & Baer, 1978). The laws of learning apply to conditioning, the pro- cesses by which responses become linked to particular stimuli, sometimes called S–R (stimulus–response) conditioning. There are two main types of conditioning: classical and operant. Classical Conditioning A century ago, Russian scientist Ivan Pavlov (1849–1936), after winning the Nobel Prize for his work on animal digestion, began to examine the link between stimu- lus and response. While studying salivation, Pavlov noted that his experimental dogs drooled not only at the smell of food but also, eventually, at the footsteps of the attendants who brought the food. This observation led Pavlov to perform his famous experiment in which he conditioned dogs to salivate when they heard a particular noise. Pavlov began by sounding a tone just before presenting food. After a number of repetitions of the tone-thenfood sequence, dogs began salivating at the sound even when there was no food. This simple experiment demonstrated classical conditioning (also called respon- dent conditioning). In classical conditioning, a person or animal is conditioned to associate a neutral stimulus with a meaningful stimulus, gradually respond- ing to the neutral stimulus in the same way as to the meaningful one. In Pavlov’s original ex- periment, the dog associated the tone (the neutral stimulus) with food (the mean- ingful stimulus) and responded to the tone as though it were the food itself. The conditioned response to the tone, which is no longer neutral but has now become a conditioned stimulus, is evidence that learning had occurred. Behaviorists see dozens of examples of classical conditioning in human devel- opment. One is called white coat syndrome, in which patients’ blood pressure rises when they see a doctor. (This used to occur for nurses as well, in their white uni- forms. To avoid this, most nurses now wear colorful blouses.) Another example of classical conditioning is very practical for parents of young children: After a period of conditioning, a child’s bladder automatically releases urine when the child sits on the toilet. Operant Conditioning The most influential North American proponent of behaviorism was B. F. Skinner (1904–1990). Skinner agreed that psychology should focus on the scientific study of behavior and that classical conditioning explains some behavior. However, he recognized another type of conditioning— operant conditioning (also called instru- mental conditioning)—in which animals do something and experience a conse- quence. If the consequence is useful or pleasurable, the animal may repeat the be- havior. If the consequence is unpleasant, the animal is unlikely to do so. Pleasant consequences are sometimes called “rewards,” and unpleasant conse- quences are sometimes called “punishments.” Behaviorists hesitate to use those words, however, because what some peo- ple think is punishment can actually be a reward, and vice versa. For example, parents punish their children by withholding dessert, by spanking them, by not letting them play, by speaking harshly to them, and so on. But a particular child might, for instance, dislike the dessert, so that being deprived of it is no punishment. Another child might not mind a spanking, especially if that is the only time the parent pays attention to the child. For that child, the intended punishment is actually a reward. Similarly, teachers sometimes punish misbehaving children by sending them out of the classroom or even suspending them from school, but if a child dis- likes the teacher and school, being sent out is actually a reward for misbehaving. In fact, recent research on school discipline finds that some measures, including school suspension, actually increase the frequency of later misbehavior (Osher et al., 2010). The true test is the effect a consequence has on the individual’s future behavior, not whether it is intended to be a reward or a punishment. A child, or an adult, who commits the same offense a second time may have been reinforced, not punished, for the first infraction. Consequences that increase the likelihood that a particular action will be repeated are called reinforcers, in a process called reinforcement (Skinner, 1953). Once a behavior has been conditioned (learned), animals (including humans) continue to perform it even if pleasurable consequences occur only occasionally, or they continue to avoid it even if punishment is rare. Almost all of our daily behavior, from socializing with others to earning a paycheck, can be understood as a result of past operant conditioning. More than half of all adult behavior is habitual, not a result of conscious thought (Neal et al., 2006). Conditioning, as described by behaviorists, led developmentalists to ask whether behavior that psy- choanalytic theory attributed to deeply rooted psychological problems was learned instead. Social Learning At first behaviorists interpreted all behavior as arising from a chain of learned responses, the result of conditioning. Behavior depended on associations between one stimulus and another or on what consequences an individual experienced. That was valid, but humans are active and social, not just reactive. Instead of responding merely to their own experiences, “people act on the environment. They create it, preserve it, transform it, and even destroy it . . . in a socially embedded interplay” (Bandura, 2006, p. 167). This insight led Albert Bandura to develop social learning theory (see Figure 2.1), which holds that humans sometimes learn without personal reinforcement. This may occur through modeling, when people copy what they see others do (also called observational learning). Modeling is not simple imitation; people model only some actions, of some individuals, in some contexts. As an example, you may know adults who, as children, saw their parents hit each other. Some such adults abuse their own partners, while others scrupulously avoid mari- tal conflict. These two responses seem opposite, but both are social learning produced by childhood ob- servation. Generally, modeling is most likely to occur when the observer is uncertain or inexperienced (which explains why modeling is especially powerful in childhood) and when the model is admired, powerful, nurturing, or similar to the observer (Bandura, 1986, 1997). If your speech, hairstyle, or choice of shoes is similar to those of a celebrity, ask yourself what made you model that person’s behavior. Admi- ration? Similarity? Social learning is connected to perceptions and interpretations of experience. One crucial interpretation involves a sense of self-efficacy, the belief that a per- sonal achievement depends on personal actions. People develop a sense of efficacy when they see other people solve problems successfully, which teaches them to have high aspirations and to strive for notable accomplishments (Bandura et al., 2001). Social learning is evident in groups of people perhaps even more than in individ- uals. For example, humans have innate aggressive impulses that, Freud thought, arose from the id. Controlling those impulses is a notable example of selfefficacy. In Sweden, where “for ages the Vikings plundered,” the people collectively “trans- formed a warring society into a peaceful one. Sweden is now a mediator for peace among warring nations” (Bandura, 2006, p. 172). Currently Swedes are proud of their collective efficacy at international cooperation and of their laws against phys- ical punishment of children. Selfefficacy explains a paradox: One might think that strict parents would be- lieve they are powerful, but the opposite seems true. Parents who feel powerless and who think their babies are strong-willed are stricter and less responsive than other parents (Guzell & Vernon-Feagans, 2004). Social learning theory provides an explanation: Their own parents may not have let them become proud of them- selves; thus, they learned to be helpless, still feeling ineffective as adults. Their lack of self-efficacy makes them overly controlling with their children. Psychoanalytic Versus Behaviorist Theories These first two theories have endured because they are provocative; they were innovative, comprehensive, and surprising. Until these theories were developed, few imagined that the unconscious or childhood experiences exert such power (psychoanalytic) or that adult behavior arises from reinforcement (behaviorist) or observation (social learning). Both theories have also been soundly criticized, with many psychologists rejecting psychoanalytic theory as unscientific (Mills, 2004) and rejecting behaviorism as demeaning of human potential (Chein, 1972/2008). Another theory, humanism (described later in this chapter), arose in direct opposi- tion to these theories. Nonetheless, like all good theories, both behaviorism and psychoanalytic theory have led to hypotheses that were examined in thousands of experiments. Here is one example. HINKING CRITICALLY What’s a Mother For? Why do children love their mothers? Both behaviorism and psychoanalytic theory originally hypothesized that mothers are loved because they satisfy the newborn’s hunger and sucking needs. In other words, “The infant’s attachment to the mother stemmed from internal drives which triggered activities con- nected with the libations of the mother’s breast. This belief was the only one these two theoretical groups ever had in common” (H. Harlow, 1986). During infancy, mothers were for feeding, and not much else. Even earlier than Freud and Pavlov, Louis Pasteur developed the germ theory of disease, proposing that invisible bacteria could make a person sick. This idea was first rejected by the medical establishment, even as thousands of new mothers and babies died (including three of Pasteur’s children). Once the germ theory was accepted, medical personnel sterilized equip- ment and washed their hands, saving millions of lives in an im- pressive example of the application of concepts first proposed as theory. However, some physicians took the theory too far. They concluded that people who kissed and hugged babies would give them germs and make them sick. Caregivers were thus kept away from hospitalized or orphaned children because “human contact was the ultimate enemy of health” (Blum, 2002, p. 35). In the 1950s, Harry Harlow (1905–1981), a psychologist who studied learning in monkeys, observed something surprising. We had separated more than 60 of these animals from their mothers 6 to 12 hours after birth and suckled them on tiny bottles. . . . During the course of our studies, we noticed that the laboratoryraised babies showed strong attachment to the folded gauze dia- pers which were used to cover the . . . floor of their cages. [H. Harlow, 1958, p. 673] In fact, the infant monkeys seemed more attached to the cloth diapers than to their bottles. This was contrary to the two prevailing theories, since psychoanalytic theory predicted that infants would love whatever satisfied their oral needs and be- haviorism predicted that infants would cherish whatever pro- vided reinforcing food. Motherless monkeys should have loved their bottles, not their floor cloths. Harlow set out to make a “direct experimental analysis” of human love via his monkeys because he believed that “the basic processes relating to affection, including nursing, contact, clinging, and even visual and auditory exploration, exhibit no fundamental differences in the two species” (H. Harlow, 1958). He raised eight infant monkeys, each caged alone with two “surrogate”...
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