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Directions: Answer the following questions/prompts about this week's lesson in short essay format (1-2 paragraphs), 300 word minimum. All answers should be your own work and in your own words.

Describe the connection between Parental Investment (PI) Theory and the difference in reproductive potential between males and females. Why is there greater variance in reproductive success among males? How does the type of mating system affect the degree of variation in number of offspring among males? Why don't we see this difference among females? Why is it useful to understand PI Theory when discussing human sexual behavior?

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Anthropology 173 The Evolution of Human Sexuality Lecture Six: Part One Parental Investment Parental Investment Theory ◼ Parental investment (PI) = investment in an offspring that increases its chance of survival and reduces parent's ability to invest in other offspring. ◼ Examples: protecting young, feeding young, producing gametes - eggs or sperm. ◼ Conceptually - PI is costly; PI is a limited resource. Robert Trivers Consequences of Sex Differences in PI ◼ ◼ ◼ ◼ ◼ Female PI is usually greater than Male PI A mating act that is inexpensive for a male triggers a large, costly investment for a female (even w/ paternal care). What limits Male RS and Female RS? Female RS - ability to convert resources (e.g., food) into offspring Male RS – limited by access to females Implications of Differences in PI ◼ Females ❑ ◼ Males ❑ ◼ evolved to be competitive; take every mating opportunity To summarize PI logic … ❑ ❑ ◼ evolved to be choosy; mate-choice error very costly Females specialize in parenting effort Males specialize in mating effort So, male & female anatomy, psychology, & behavior differ in predictable ways Buss and Schmitt 1993 Buss and Schmitt 1993 Clark and Hatfield 1989 ◼ Had research assistants approach strangers on campus and say: “I’ve been noticing you around campus. I find you to be very attractive.” ❑ ❑ ❑ “Would you go out with me tonight?” “Would you come over to my apartment tonight?” “Would you go to bed with me tonight?” ◼ Men said: ❑ ❑ ❑ ◼ “Why do we have to wait until tonight?” “I can’t tonight but how about tomorrow?” Apologies: “I’m sorry, I’m married.” Women said: ❑ ❑ “You’ve got to be kidding!” “What’s wrong with you, leave me alone.” The Coolidge Effect ◼ In nearly every species, males show renewed sexual arousal when introduced to a new female Sex Variation in Reproductive Success ◼ Reproductive potential: number of surviving offspring that could potentially be produced by an individual (number of eggs, number of ejaculations) Genghis Khan ◼ As many as 8 percent of the men dwelling in the confines of the former Mongol empire bear Y chromosomes that seem characteristic of the Mongol ruling house. ◼ Some 16 million men, or half a percent of the world's male population, can probably claim descent from Genghis Khan. Anthropology 173 The Evolution of Human Sexuality Lecture Six: Part Two Parental Investment Female Reproductive Potential ◼ “Wife of Feodor Vassilyev”: 69 children from 27 pregnancies (Russia 1800s) ◼ Madalene Granata: 15 sets of triplets (Italy, 1839 to 1886) ◼ Fatma Saygi (at 28): 6 sets of triplets But… ◼ Males can have a lot of offspring, but are also more likely to have few ◼ Females have less variance in reproductive success PI and Survival ◼ Due to the increased benefits to males of greater competition and also the greater costs of not competing, males put more energy into mating effort ◼ This increased energy into mating effort may be detrimental to survival, much as costly armaments and ornaments can decrease survival Cautions about PI Theory ◼ In some cases, females are selected to be promiscuous ❑ particularly in primates like chimpanzees, to combat infanticide ❑ or to encourage sperm competition ◼ In some cases, males may be choosy (especially when males invest equally or more than females) ◼ Females can be competitive, especially when males invest in offspring ◼ Sex ratio in a population can affect which sex is the limited resource Mating Systems and PI ◼ The variance in male reproductive success is closely tied to the mating system ❑ Monogamous males have about the same number of children as females ❑ Polygynous males can have many more children ◼ Thus, male-male competition should be greater in polygynous mating systems ◼ Males should be choosier in picking monogamous mates Females Can Gain from Cuckoldry ◼ Cuckoldry is when a female cheats on her pair bonded partner ◼ Female gains good genes, extra investment, etc… ◼ The pair bonded male ends up raising another male’s child ◼ This is costly to the male, since he is helping someone else’s genes rather than his own ◼ But females should be choosy in picking their extra pair partners as well Conclusions ◼ Sexual selection includes: ❑ Intra-sexual competition (between members of the same sex) ❑ Inter-sexual selection (mate choice) ❑ Inter-sexual conflict ❑ Both pre- and post-copulatory selection ◼ In most species males are competitive and females choosy because females invest more in offspring, while males are limited only by access to mates ◼ There are many exceptions to this general pattern
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RUNNING HEAD: MALE AND FEMALE REPRODUCTION DISCUSSIONS

Male and female reproduction discussions
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MALE AND FEMALE REPRODUCTION DISCUSSIONS

Introduction
Parental investment theory explains that any resource invested for instance time, in relation to
the raising of an offspring is likely to hinder the ability of the parent(s) involved to cater for other
children altogether. The...


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