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The Evolution of Human
Physical Attractiveness
Steven W. Gangestad and Glenn J. Scheyd
Department of Psychology, University of New Mexico, Albuquerque, New Mexico
87111; email: sgangest@unm.edu, gscheyd@unm.edu
Annu. Rev. Anthropol.
2005. 34:523–48
The Annual Review of
Anthropology is online at
anthro.annualreviews.org
doi: 10.1146/
annurev.anthro.33.070203.143733
c 2005 by
Copyright
Annual Reviews. All rights
reserved
0084-6570/05/10210523$20.00
Key Words
beauty, sexual selection, evolutionary psychology, evolutionary
anthropology, costly signaling
Abstract
Everywhere the issue has been examined, people make discriminations about others’ physical attractiveness. Can human standards
of physical attractiveness be understood through the lens of evolutionary biology? In the past decade, this question has guided much
theoretical and empirical work. In this paper, we (a) outline the basic adaptationist approach that has guided the bulk of this work,
(b) describe evolutionary models of signaling that have been applied to understand human physical attractiveness, and (c) discuss
and evaluate specific lines of empirical research attempting to address the selective history of human standards of physical attractiveness. We also discuss ways evolutionary scientists have attempted to
understand variability in standards of attractiveness across cultures
as well as the ways current literature speaks to body modification in
modern Western cultures. Though much work has been done, many
fundamental questions remain unanswered.
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Contents
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INTRODUCTION . . . . . . . . . . . . . . . . .
METATHEORY AND THEORY . . .
The Adaptationist Framework:
Basic Concepts . . . . . . . . . . . . . . . .
Sexual Selection and Signaling
Theory . . . . . . . . . . . . . . . . . . . . . . .
Are Honest Signaling Systems
of Quality Ubiquitous? . . . . . . . .
Genetic versus Direct Benefits . . . .
Multiple Signals . . . . . . . . . . . . . . . . . .
Mutual Mate Choice . . . . . . . . . . . . .
FEATURES ASSOCIATED WITH
ATTRACTIVENESS: WHAT
DO THEY SIGNAL? . . . . . . . . . . . .
Facial Sexual Dimorphism . . . . . . . .
Facial Averageness . . . . . . . . . . . . . . . .
Facial Symmetry . . . . . . . . . . . . . . . . .
Female Body Form . . . . . . . . . . . . . . .
Male Physique . . . . . . . . . . . . . . . . . . .
BODY MODIFICATION . . . . . . . . . . .
CURRENT AND FUTURE
DIRECTIONS . . . . . . . . . . . . . . . . . .
The Precise Benefits Generating
Preferences . . . . . . . . . . . . . . . . . . .
The Overlapping and Independent
Contributions of Preferred
Features . . . . . . . . . . . . . . . . . . . . . .
The Integration of Different
Signals . . . . . . . . . . . . . . . . . . . . . . . .
The Conditional Nature of
Preferences . . . . . . . . . . . . . . . . . . .
The Moderating Effect of
“Non-Physical” (or Nonstatic)
Features . . . . . . . . . . . . . . . . . . . . . .
SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . .
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INTRODUCTION
Intensive study of human physical attractiveness in the social sciences was prompted by
a serendipitous finding by Hatfield and colleagues in 1966. These researchers randomly
paired college men and women for a blind
date. In return, participants filled out per524
Gangestad
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sonality and interest measures, background
questionnaires, and a survey following the
date. A key question was whether they were
interested in a subsequent date with their
partner. None of the researchers’ own hypotheses were supported. Rather, only one
variable—added as an afterthought—reliably
predicted interest: their partners’ physical
attractiveness.
Research over the past four decades has
demonstrated profound and broad-reaching
implications of physical attractiveness for people’s lives. As might be expected, attractive
people have greater choice in mating markets and hence are able to secure consensually more desired partners. But attractive
people are treated differently from others
more generally, leading them to have better
jobs, higher incomes, and more friends than
others—indeed, achieve more desirable outcomes in most spheres of life people consider
important (e.g., Langlois et al. 2000).
Physical attractiveness matters to mate
choice not only among U.S. college students.
Buss (1989) surveyed people from 37 cultures around the world about mate preferences. The U.S. samples rated the importance
of physical attractiveness only slightly above
average for the cultures. In traditional groups
as well, e.g., the Ache of Paraguay ( Jones &
Hill 1993), the Shiwiar of Equador (Sugiyama
2004), the Machigenka of Peru (Yu & Shepard
1998), and the Hadza of Tanzania (Wetsman
& Marlowe 1999), individuals have reliable
standards of attractiveness. Indeed, a recent
meta-analysis concluded that people in different cultures generally agree on who is
attractive (Langlois et al. 2000). Physical attractiveness appears to have important implications in traditional cultures too; attractive Ache women, for instance, have
greater reproductive success (Hill & Hurtado
1996).
Symons’s (1979) Evolution of Human Sexuality offered the first intensive analysis of
physical attraction as an outcome of natural selection. It inspired Buss’s (1989) survey
and spawned research on features considered
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attractive cross-culturally (e.g., Jones & Hill
1993, Cunningham et al. 1995). Research
guided by evolutionary thinking steadily intensified over the past 15 years. Since 1990,
nearly 300 articles with the keywords “physical (or facial) attractiveness” as well as “selection” or “evolution” in their titles or abstracts
have appeared in scientific journals. Those
published in the five years since 2000 outnumber those appearing in all of the 1990s
(and, indeed, will probably soon outnumber those published in all of the twentieth
century!).
We first discuss the adaptationist framework that has guided evolutionary analyses
of attractiveness, with emphasis on biological signaling theory. We then review recent research in light of this framework and
conclude with key issues for future research.
METATHEORY AND THEORY
The Adaptationist Framework:
Basic Concepts
As a research strategy, adaptationism seeks to
identify adaptations and elucidate the selection pressures that forged them in an organism’s evolutionary past. In its current form, it
crystallized in the 1960s and 1970s [heavily influenced by the writings of George Williams
(1966)] and now dominates the study of animal behavior in biology (e.g., Krebs & Davies
1993, 1997). It also guides most evolutionary work on human attractiveness. We review
briefly some basic concepts and tools. (For a
more extensive discussion, see also Andrews
et al. 2002.)
Traits.
Biologists use the term trait to refer
to aspects of organisms’ phenotypes. A liberal
definition allows a trait to be any aspect of
the phenotype that can be discriminated on
the basis of any criterion—its causes, effects,
appearance, etc.—and includes dispositional
traits (e.g., the disposition to develop calluses
with friction; the disposition to choose mates
with particular qualities).
Adaptation.
The word adaptation has two
meanings in evolutionary biology (Gould &
Vrba 1982). It is the process by which natural
selection modifies the phenotype and generates traits whose effects facilitate the propagation of certain genes over others, thereby
causing evolution. It also refers to the endproducts of that process—i.e., the traits that
have been constructed by a process of phenotypic modification by natural selection for
a particular gene-propagating effect. An effect refers to the way, or ways, in which an
aspect of the phenotype interacts with the environment (e.g., Williams 1992). At least one
effect of an adaptation is beneficial in an evolutionary sense; this effect is referred to as
the adaptation’s function. A function is an effect that caused the trait to evolve—that is,
an effect that enhanced the reproductive success of the trait’s bearers over others lacking
the trait. Crudely put, the primary function of
eyes is seeing; the primary function of wings is
flight.
Byproducts.
A small minority of traits
qualifies as adaptations. Byproducts (or spandrels; Gould & Lewontin 1979) evolved
merely because they were linked with other
traits that had beneficial effects and hence
were carried along with selection for adaptations. For example, vertebrate animals
evolved skeletal systems of calcium phosphate
(perhaps ancestrally for the function of storing calcium, but modified for the function of
structural rigidity necessary for locomotion;
e.g., Ruben & Bennett 1987). Calcium phosphate is white and hence so too are bones. The
whiteness of bones, however, is not an adaptation. It is a byproduct of selection for other
properties of calcium phosphate.
Energetic trade-offs.
Organisms can be
thought of as entities that capture energy
from the environment (e.g., through foraging,
hunting, or cultivating) and allocate it to reproduction and survival-enhancing activities.
Energy does not come for free. Were individuals able to expend unlimited energy at no
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cost, in principle they could evolve to grow
and develop so rapidly they could begin reproducing immediately after birth, massively
produce offspring, and preserve themselves
such that they never age. In biological reality,
however, individuals are constrained by finite
energy “budgets” (themselves earned through
energy and time expenditures). Allocation of
finite energy and time budgets entails tradeoffs and hence forces decisions about the relative value of possible ways to spend. Individuals should be expected to evolve adaptations
that lead them to allocate their budgets in ways
that enhance their fitness. Hence, for example, selection does not favor ever-increasing
clutch sizes in birds. Rather, selection presumably favors strategies of producing and raising
offspring that maximize the overall reproductive success of offspring through an optimal
balance of offspring number and quality,
as constrained by energy and time budgets
(see, e.g., Seger & Stubblefield 1996, Kaplan
& Gangestad 2005). As we emphasize later,
a key notion in the study of attractiveness is
that the amount of effort that individuals can
dedicate to a biological signal found attractive
by the other sex is constrained by their energy
budgets.
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Cost-benefit modeling.
Adaptationists
often use quantitative optimization models
to try to understand how selection operates
on phenotypes, given trade-offs (e.g., Seger
& Stubblefield 1996, Winterhalder & Smith
2000). A model has one or more actors (e.g.,
two or more individuals engaging in social
interaction, etc.) expressing the phenotypes
that the theoretician is trying to understand.
The payoffs of the model are expressed in a
currency, such as actual fitness units or some
correlate of fitness (e.g., units of energy).
The decision set is the suite of phenotypic
or behavioral options available for pursuing
payoffs, and selective constraints delineate
how these options translate into costs and
benefits (typically dictated by constraints
of energy and time budgets). The optimal
phenotypic or behavioral option is the
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one that maximizes net benefits under the
constraints. Complexities can be taken into
account. For instance, optimal strategies may
be contingent on the condition or phenotype
of the individual (conditional or phenotypelimited optima). Hence, as we’ll see, an
important theme of biological signaling
theory is that the optimal intensity of a signal
may vary as a function of individuals’ own
condition. (See Parker & Maynard Smith
1990).
The special design criterion for identifying adaptations.
Evolutionary biologists
are interested in understanding adaptation.
Because adaptations don’t come with labels,
however, their identification requires inference. The major criterion used is special design (e.g., Williams 1966; Thornhill 1990,
1997). A feature exhibits special design if it
proficiently performs a specific function; and
moreover, it is difficult to imagine any alternative evolutionary process that would have led
to the feature or its details other than selection for that function. For instance, eyes are
good for seeing and it’s difficult to imagine
an evolutionary process that would have led
to many of their details other than selection
for their optical properties, that is, for seeing. Evidence for design is not only evidence
that adaptation has been at work; it’s evidence
that the organism has been shaped by particular selection pressures. Just as wings and
eyes are telltale signs of historical selection for
flight and seeing, respectively, certain psychological features of modern humans (e.g., patterns of attraction to mates and their features)
may be telltale signs that particular selection
pressures shaped the minds of ancestral humans (e.g., selection for a signaling system
due to particular benefits associated with the
signal).
Attractiveness and beauty as an outcome
of adaptation.
Individuals find other individuals attractive as a result of the latter possessing specific favored traits. Obviously, however, attractiveness reflects traits in
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perceivers as well: Perceivers have traits leading them to find some features more attractive
than others. Adaptationist researchers have
typically adopted the working hypothesis that
perceiver traits are adaptations—evolved as a
result of their having benefits for perceivers—
or, as the title of an article by Symons proclaims, “Beauty is in the adaptations of the
beholder” (1995).
Generally speaking, tendencies to be attracted to particular traits in individuals of
the opposite sex are presumed to have benefited their bearers because individuals’ own
reproductive success (or that of their offspring) is affected (or, more precisely, was
affected ancestrally) by qualities of the individuals with whom they mate. In broad
terms, evolutionary biologists delineate two
types of benefits that mates provide: first, genetic benefits to offspring—i.e., endow offspring with superior ability to survive; second, material benefits to the perceiver such
as food, care for offspring, physical protection for self or offspring, or avoidance of disease. Individuals disposed to mate with others
who enhanced their own fitness would have,
ceteris paribus, out-reproduced those not so
disposed. Hence, selection may have favored
dispositions to be attracted to mates who
possessed qualities that signal (or ancestrally
signaled) delivery of benefits. Adaptationist
researchers typically adopt a working hypothesis that many of people’s tendencies to find
specific features attractive are outcomes of this
kind of historical selection (though see our
discussion of alternative, sensory bias models
below).
Once individuals of one sex prefer particular qualities, the preferences exert selection
pressures on the preferred traits. Individuals
who possess preferred traits, by virtue of their
enhanced ability to exercise choice in a mating market, have greater reproductive success.
Selection hence leads individuals to expend
energy and time to display favored traits. As
Charles Darwin himself recognized (1871),
such selection can in theory lead to the evolution of extravagant ornaments, even those
detrimental to an animal’s viability, provided
they gave a sufficient advantage in the realm
of mating. In turn, selection may come to exert pressures on perceivers’ greater ability to
discern truly favored traits. Preferences and
the traits they prefer coevolve.
Sexual Selection and Signaling
Theory
Physical traits individuals are selected to find
attractive may be thought of as signals of underlying qualities. The coevolution of preferences and preferred traits, then, can be
thought of as the evolution of a signaling
system, which entails that one sex (signalers)
possess signals and the other sex (receivers)
possess psychological (cognitive and motivational) capacities to perceive and act upon
(e.g., be attracted to) those signals. (In a given
species, both sexes may evolve preferences
and hence be receivers in signaling systems,
of course.) Signals of underlying quality or
condition have received the greatest attention
from biological signaling theorists. Quality or
condition refers to an individual’s ability to
successfully interact with the environment to
acquire and effectively expend energetic resources (e.g., Rowe & Houle 1996). Superior
condition has been associated with the concept of health (e.g., Grammer et al. 2003).
The concept of health it implies, however, is
much broader than simply the absence of disease; it implies greater phenotypic fitness or
resourcefulness. Indeed, as discussed below,
in particular circumstances individuals of superior condition may even be more prone to
disease than others. The term health, then, is
generally a poor stand-in for biologists’ notion of condition.
Individuals in superior condition may
make better mates for a variety of reasons: fitter genes to pass on to offspring (e.g., a relative
absence of mildly harmful mutations; Houle
1992); greater ability to provide material benefits such as protection or food; greater fertility and ability to reproduce (e.g., more viable
sperm in the case of males or greater ability to
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conceive and carry offspring through gestation and lactation in the case of females); and
a relative absence of disease. General models of signals of quality do not speak to the
precise nature of the benefits associated with
choosing a mate of superior quality, though
researchers are often interested in determining these benefits.
A signaling system may be said to be at
equilibrium when neither the signaling sex
nor the receiving sex benefits from a change
(i.e., in signal sent or preference exercised)
given that the other retains its strategy. For
a signal to be a valid indicator of one’s quality
at equilibrium, a reliable relation between the
signaler’s quality and the signal strength must
persist. Zahavi (1975) introduced the idea that
it is the very costliness of a trait that ensures
its honesty. He specifically proposed that animals may signal that they are of superior quality with a “handicap”—a feature that imposes
a cost on the individual. Zahavi did not provide an optimization model of this process;
his argument was a verbal one. The basic intuitive notion is that individuals who can afford a
large handicap must be more viable than individuals who have smaller handicapping traits.
Big signalers can afford to “waste” some of
their viability and still have residual viability greater than that of small signalers, and
this fact presumably renders the handicapping
trait an “honest” signal of viability. (In this
context, a “bigger” signal need not be larger.
Rather, the term indicates greater cost for individuals, on average, to produce. The cost
itself may be due to the signal’s size, its complexity, or any other characteristic requiring
effort to produce. Costs can also be mediated
socially, for some signals let competitors know
that their bearers should be tested through
competition.)
Grafen (1990) was the first to quantitatively model handicapping. He assumed that
all individuals, regardless of quality, obtain the
same fitness benefits from a particular level of
a signal (however, see Getty 1998). The signal
can evolve to display quality, according to this
model, when the fitness costs (in the currency
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of mortality) associated with developing and
maintaining a particular level of the signal are
less for individuals of higher quality than for
individuals of lower quality. In that instance,
the size of the handicap that maximizes net
fitness (benefits minus costs) is larger for individuals of higher quality than for individuals
of lower quality. The signal “honestly” conveys fitness, then, simply because it is not in
the interest of individuals of lower quality to
“cheat” and develop a larger signal; the viability costs they would suffer exceed the fertility
benefits they would derive from the increased
signal size.
Recent developments in honest signaling
theory have furthered and revised our understanding of it. Despite the intuitive appeal,
systems of mate choice via signals of condition need not imply that the biggest signals are
sent by the most viable individuals. For signals
to be reliable, higher quality individuals need
only higher efficiency, i.e., a greater fitness
return from a marginal increase in signal investment (Getty 2002). Modeling has shown
that individuals of highest quality may have
the same, higher, or lower viability than small
signalers at equilibrium, depending on specific parameters of the system. A key parameter is the expense paid by receivers for preferring those with big signals over others, most
notably, the cost of search time. Individuals
with strong preferences for a signal of a certain
size may delay mating and hence lose valuable
time reproducing. A preference may be very
cheap in some species—e.g., lekking species in
which males collectively gather and display to
females, who can assess relative quality without sacrificing search time. In such species, a
few males who “win” the display contest may
garner nearly all the matings, which in turn
boosts the intensity with which males capable of sending strong signals will do so, sometimes beyond the point at which high quality
males have reduced their viability to that of
their lower quality rivals. Oddly, then, quality and mortality can actually become positively correlated in a population, with the
highest quality individuals dying, on average,
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at younger ages than lower quality individuals (Kokko et al. 2002). When females pay
relatively high costs for their preference in
relation to its benefits, the system will not
drive signal intensity to be as great (i.e., signals themselves will be less costly at equilibrium) and, furthermore, individuals of highest quality are unlikely to invest in signals to
the extent that they actually have lower viability than individuals of lower quality. Similarly,
the association between quality and parasite
load (disease-level) can be positive, negative,
or negligible, depending on the system (Getty
2002).
Are Honest Signaling Systems
of Quality Ubiquitous?
A model that does not assume an association between signal intensity and quality is
the sensory bias model (e.g., Kirkpatrick &
Ryan 1991). In this model, one sex has a bias
to prefer individuals of particular qualities because that bias has advantages in realms other
than mating. For instance, redness may be
preferred in features of mates because redness
signals ripeness of fruit and a sensory bias to be
attracted to redness spills over into domains
other than food selection. (Here, the bias applied to mates is a byproduct of an adaptation
for food choice.) Fisher (1930) famously described a process whereby a small initial preference ultimately leads to extreme traits and
preferences through “runaway” selection. If
a particular trait in one sex is preferred in
mates due to sensory bias in the other sex,
then genes disposing stronger preference for
the trait could spread because they become
linked with genes predisposing the preferred
trait. In essence, genes for strong preference
“piggyback” on the success of the preferred
trait, leading to stronger and stronger
preferences and more and more extreme
traits.
A distinct variant of a sensory bias model
is the “chase-away” model (Holland & Rice
1998). It assumes that individuals of the
choosing sex with a sensory bias nonadaptively
applied to mate choice pay a cost for it (e.g.,
increased search time) and, hence, have lower
reproductive success than those who are “resistant” to the bias. This purportedly leads to
selection for more intense signals in the other
sex, ones than overcome the resistance of a
greater proportion of choosers, which in turn
leads to selection for a higher threshold of resistance. Over time, the chase-away process
results in extreme manifestations of the trait.
Kokko et al. (2003) recently argued that
runaway or chase-away processes due to small
initial sensory biases are unreasonable models of signaling equilibria. In each case, the
signal that evolves is presumed to become increasingly costly. As costs increase, individuals
of highest quality will be able to produce the
signal more efficiently than others—precisely
the condition in which a signal comes to
honestly convey quality. Inevitably, then, signals initially preferred merely due to sensory bias should become correlated with quality through runaway or chase-away processes.
Rather than conceptualizing sensory bias or
chase-away models as competitors of honest
signaling models, then, Kokko et al. (2003)
argues that sensory bias may be the starting
point of a process that leads to honest signaling. Such biases may explain how preferences for seemingly arbitrary traits—ones
prior to the evolution of the signaling system were probably not associated with quality
(e.g., a tail brighter or larger than average)—
can get off the ground, such that these traits
ultimately become correlated with quality.
Honest signals of quality need not initially
be uncorrelated with quality, however. Features may covary with quality prior to being
signals because individuals of higher quality
pay lower marginal costs for them—e.g., in
some species, larger individuals or those better able to intrasexually compete may possess
higher quality. Preferences for these traits (or
natural correlates of them) may then evolve,
which further intensifies them by increasing
the benefit of investing in the development of
these traits. As we discuss later, a number of
features preferred by humans may well have
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correlated with quality prior to their evolution
as signals.
choice is based only on males’ ability to provide genetic benefits.
Genetic versus Direct Benefits
Multiple Signals
Again, honest signaling of quality can evolve
through either benefits that directly enhance
reproductive success (e.g., food, protection,
lack of contagious disease) or genetic benefits
passed on to offspring. In some instances, both
may account for the preference. For instance,
males in a multi-male primate group better able to protect offspring than others and
hence providing direct benefits to choosers
may well possess genes associated with quality
as well.
In mating systems in which males and females form socially monogamous (or mildly
polygynous) pairs and males invest heavily in
offspring (e.g., many bird species), direct benefits and indirect benefits may covary negatively. This should particularly be true when
females are not sexually monogamous and
offspring are frequently sired by “extrapair”
males (also true of many bird species; e.g.,
Petrie & Kempanears 1998). In such cases,
males of superior condition may optimize
their allocation of effort by investing less in
offspring and more in efforts to secure extrapair matings (as they may succeed more often than males of lower quality). Where direct and indirect benefits correlate negatively,
either can be stronger; females may have a
preference for males offering less direct benefit or less indirect benefit. Moreover, female
preferences may vary depending on whether
they are selecting a social partner or an extrapair mate. In collared flycatchers on the island of Gotland, for instance, females have no
clear preference for males having a relatively
large forehead patch, an honest signal of quality (Qvarnström 1999). When choosing extrapair partners, however, females clearly prefer
large-patched males. In theory, direct and genetic benefits of social partners negatively covary and cancel out. (Males with larger patches
feed offspring less.) Extra-pair partners, however, provide no direct benefits and, hence,
In many species, mate choosers attend to multiple signals, sometimes transmitted through
different sensory channels (e.g., both olfactory and visual cues). One possible explanation is error in signal transmission; multiple signals of the same quality evolve because
each adds incremental information that others do not (e.g., each signal or its perception is
not perfectly correlated with quality; Grafen
& Johnstone 1993). Alternatively, such mixing might be explained through a combination of constrained transmission time and a
need to convey abundant information (Endler
1993). As a parallel, one might imagine the use
of both hand gestures and oral instructions
in giving directions to a driver stopped at a
red light. A third explanation is that signals
carry information about different qualities
altogether.
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Mutual Mate Choice
In many species, sexual selection on signals
is much greater in one sex than the others.
In mammalian species, females are typically
a limiting reproductive resource and, hence,
males compete through intrasexual competition and through signaling for females. Selection on female signaling is much weaker,
as males may seldom turn down sexual opportunities with females. In species in which
both males and females invest substantially
in offspring, however, mutual mate choice
may evolve (e.g., Kokko & Johnstone 2001),
whereby both sexes are selected to display desired mate qualities. Although the extent to
which human male assistance to offspring has
historically functioned to increase offspring
quality or, alternatively, to increase access to
mates is hotly debated (e.g., Kaplan et al.
2000, Hawkes et al. 2001), in any case mutual
mate choice appears to characterize human
cultures. Both men and women discriminate
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the desirability of potential mates, partly on
the basis of physical qualities.
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FEATURES ASSOCIATED WITH
ATTRACTIVENESS: WHAT DO
THEY SIGNAL?
Researchers have focused attention on three
facial features found attractive across many
cultures: sexual dimorphism, averageness, and
symmetry. In addition, researchers have examined the effect of several nonfacial bodily features on attractiveness, most notably,
female waist-to-hip ratio and male body type.
Facial Sexual Dimorphism
Men’s and women’s faces differ in a number of ways. On average, men’s chins are
longer and broader than women’s. Development of the brow ridge renders men’s
eyes smaller (relative to total face size) and
narrower than women’s (e.g., Gangestad &
Thornhill 2003a). Women’s cheekbones are
more gracile and their lips fuller. During adolescence, testosterone promotes growth of the
lower face (see Swaddle & Reierson 2002).
Estrogens may cap growth of bones during
puberty, contributing to sexual dimorphism
as well. Despite variation in facial proportions across human groups, sex differences exist wherever they have been examined (e.g.,
Jones & Hill 1993). We refer to the aggregate
differences between men’s and women’s faces
as facial masculinity versus femininity.
The attractiveness of female facial femininity. Facial femininity is attractive in
women; highly attractive women’s faces are
more feminine than average (e.g., Johnston &
Franklin 1993, Perrett et al. 1994). This finding has been replicated in a wide variety of
human groups (e.g., United Kingdom, Japan,
Russia), including traditional South American
groups with little to no exposure to Western
standards of beauty (e.g., Ache; Jones & Hill
1993). Men prefer female faces with relatively
small chins, large eyes, high cheekbones, and
full lips (e.g., Cunningham 1986).
Several theories explaining men’s attraction to femininity have been offered.
Facial femininity reflects babyness, preferred due
to sensory bias. An early theory is that feminine features such as large eyes and small
chin reflect “babyness” (Cunningham 1986,
Johnston & Franklin 1993, Jones 1995). People may be disposed to respond to babies with
care and, hence, be attracted to baby-like features (Jones 1995). Ancestral females who exploited this preference may have been advantaged over those who didn’t, driving the sexual
dimorphism itself.
This theory encounters two major problems. First, some attractive feminine features
are not baby-like. Babies have puffy, protruding cheeks (e.g., McArthur & Apatow 1984),
whereas men find gracile, high cheekbones attractive in women’s faces (e.g., Grammer &
Atzwanger 1994). Second, as noted earlier,
even a sensory bias model should expect that,
as a trait is driven to be more extreme, some
individuals should be better able to display it
and, hence, it should become correlated with
quality (Kokko et al. 2003).
Female facial femininity marks sex appropriateness. The view that attractive displays exaggerate species- or sex-typical traits to foster
choice of a species- or sex-appropriate partner
was prominent in the first half of the twentieth century (see, for a review, Cronin 1991).
It might also expect women to particularly
prefer highly masculine faces, which as we
discuss below is not the case. Furthermore,
once again, selection due to a bias favoring
a trait uncorrelated with quality should ultimately result in covariation between the trait
and quality.
Female facial femininity is a marker of reproductive value. Reproductive value (RV) is the
expected residual reproductive success of an
individual, generally based on age (Fisher
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1930). RV is maximal when women reach reproductive age and diminishes thereafter. If
men ancestrally mated serially with the same
partners throughout their reproductive career (e.g., Kaplan et al. 2000), men may have
maximized their fertility by selecting mates
with maximal RV (Symons 1979). As women
age, their facial proportions become less feminized, probably due to accumulated exposure
to androgens (see Thornhill & Gangestad
1993). Men’s preference for facial femininity,
then, could reflect selection for age-based RV.
RV could account for selection and maintenance of a preference favoring facial femininity. Once again, however, women should
have been selected to exaggerate and prolong the period of facial femininity, with some
women better able to do so than others, ultimately leading facial femininity to be a cue of
quality.
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RV: reproductive
value
Facial femininity is a marker of female quality
or condition. Female femininity may signal
reproductive condition and ability to dedicate energy to offspring production. Women’s
production of estrogen and fertility status
are designed to be sensitive to conditions
that affect their ability to carry and lactate
for offspring—their energy condition (total
stored energy in fat), energy balance (residual energy consumed minus expended available for reproductive effort), and energy flux
(total energetic output). Women have diminished ovarian function when they do not have
fat stored for reproduction, do not reliably
take in calories that surpass energy expenditure, or incur extreme (either very low or
very high) energetic demands (e.g., Ellison
2001, 2003). Extreme instances result in
amenorrhea, but normal variation affects the
production of ovarian hormones, including
estrodiol, and thereby ovarian function, such
that female fecundity varies along a continuum. Energy balance and flux appear to have
larger effects than energy status, at least in the
United States (Lipson & Ellison 1996). Facial
femininity does not change drastically with
immediate circumstances, but it could index
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women’s accumulated history of energy balance and flux appropriate for reproduction.
The advantages of attraction to women
with such a history (at least ancestrally) could
be twofold. First, it could be a cue of direct
benefits, as it could reflect lower disease incidence, better development due to favorable
levels of parental investment, greater ability
to forage effectively, etc., all affecting current reproductive capabilities. Second, such
a history could be associated with genetic
benefits to offspring. Women with more efficient metabolisms due to fewer mutations
(and hence more favorable energy balance,
controlling for energy intake) or genotypes
more resistant to extant pathogens would produce genetically more fit offspring.
Evidence pertaining to whether women’s
facial femininity or attractiveness are associated with health is mixed. Hume &
Montgomerie (2001) and Henderson &
Anglin (2003) found associations between facial attractiveness and relative absence of
past health problems and longevity, respectively (see also Langlois et al. 2000; compare Kalick et al. 1998). Rhodes et al. (2003)
reported no association between rated female facial femininity (in adolescence) and
actual health records, whereas Thornhill
& Gangestad (2005) found facial femininity (measured from digitized photographs)
to predict recent history of respiratory infections and antibiotic use. Body symmetry
(aggregated across fingers, wrists, ears, elbows, etc.) measures developmental stability,
a lack of perturbations during development
due to infection, mutations, and other stresses.
Koehler et al. (2004) reported that women
with greater body symmetry are perceived
to have more feminine faces; Gangestad
& Thornhill (2003a) found no association. No
study has examined facial femininity in relation to health in traditional societies exposed
to ecological circumstances reasonably similar to ones encountered by ancestral societies,
in which the childhood mortality rates due to
disease may typically have been 30–50% (e.g.,
Hill & Hurtado 1996) and energy budgets
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were constrained. Moreover, no one to our
knowledge has explored associations between
ovarian function and facial femininity. Although we suspect that preference for female
facial femininity has been maintained because
of this trait’s historical association with both
RV and fecundity, the latter link requires additional evidence.
Attractiveness in relation to male facial
masculinity. One might suspect that, just
as men find feminine faces attractive, women
might be attracted to masculine faces. In fact,
no clear preference exists; studies have found
a female preference for somewhat masculine
faces (Keating 1985, Johnston et al. 2001),
preference for feminine faces (e.g., Perrett
et al. 1998, Penton-Voak et al. 1999), and no
systematic preference either way (e.g., Cunningham et al. 1990, Jones & Hill 1993,
Swaddle & Reierson 2002).
Male facial masculinity nonetheless covaries with certain desired male traits. Across
a variety of cultures, men with masculine faces
are perceived to be and probably are (Mueller
& Mazur 1997) socially dominant (e.g.,
Keating et al. 1981, Mazur et al. 1984). Kung
San bushmen with broad chins and robust
bodies have relatively high reproductive success (Winkler & Kirchengast 1994). One argument is that testosterone promotes male
mating effort, which partly involves malemale competition, and that men’s condition
affects the extent to which they can effectively
dedicate effort to mating (in a way analogous
to how women’s condition affects their ability
to dedicate effort to reproduction). Variation
in condition therefore gives rise to variation in
testosterone metabolism, which, during adolescence, causes variation in facial masculinity. Men with more masculine faces may be
tested in male-male competition, a cost that
may ensure its honesty as a signal of condition. Consistent with this interpretation,
two studies have found associations between
male facial masculinity and reported health
(Rhodes et al. 2003, lower half of the distribution only; Thornhill & Gangestad (2005),
Zebrowitz & Rhodes 2004). Gangestad &
Thornhill (2003a) found that men with masculine faces have greater body and facial symmetry, though Koehler et al. (2004) did not.
Among childless men in a rural village in
Dominica, body symmetry positively predicts
testosterone levels (controlling for age; S.W.
Gangestad, R. Thornhill, M.V. Flinn, L.K.
Dane, R.G. Falcon, C.E. Garver-Apgar, M.
Franklin & B.G. England, unpublished data).
(Male facial masculinity may be weakly associated with current testosterone level; PentonVoak & Chen 2004.) As male testosterone
varies as a function of a variety of factors,
including mating status and paternity (e.g.,
Burnham et al. 2003), however, facial masculinity may better index levels during adolescence and early adulthood. If adolescence
is characterized by relatively intense malemale competition, facial masculinity may
nonetheless reflect condition.
If male facial masculinity covaries with
condition, as conjectured, why do women not
consistently prefer masculine faces? PentonVoak et al. (1999) speculated that women face
a trade-off: Although more dominant and possibly more fit, masculine men may be less
willing to invest exclusively in partners and
help care for offspring. Hence, just as female
collared flycatchers do not particularly prefer males with large forehead patches as social partners, women do not prefer more masculine men as mates. As this view expects,
men with feminine faces are perceived to be
warmer, more agreeable, and more honest
than men with masculine faces (see Fink &
Penton-Voak 2002).
According to this view, attraction to male
masculinity should have been shaped by selection to be conditional—depend on conditions
that affect (or ancestrally would have affected)
the relative value of (possibly heritable) condition and paternal investment. Evidence
suggests that it is.
Preference varies with phase of the ovulatory cycle. Women’s mate preferences vary
across their ovulatory cycles. When normally
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ovulating (e.g., nonpill-using) women are
close to ovulation (and hence fecund), they
are particularly attracted to the scent of symmetrical men (Gangestad & Thornhill 1998,
Thornhill & Gangestad 1999, Rikowski &
Grammer 1999, Thornhill et al. 2003), deep,
masculine male voices (Putz 2005), and more
confident, intrasexually competitive male behavioral displays (Gangestad et al. 2004), particularly (where it has been examined; e.g.,
Gangestad et al. 2004) when they evaluate
men as sexual partners (their “sexiness”) rather
than as long-term mates. Changes in preferences across the cycle may reflect female design to weigh signals of heritable condition
more heavily when they are fertile, particularly when selecting a sex partner. Interestingly, then, the face that women most prefer when close to ovulation is more masculine than the face most preferred when they
are in the luteal phase [Penton-Voak et al.
1999 (United Kingdom, Japan), Penton-Voak
& Perrett 2000 (United Kingdom), Johnston
et al. 2001 (United States, Austria)]. Furthermore, the effect is specific to female attraction
to men as sex partners, not long-term social
mates (Penton-Voak et al. 1999).
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Preference varies as a function of relationship context. The face women find most
attractive in short-term mates is more masculine than the face they find most attractive in long-term mates (Penton-Voak et al.
2003).
More attractive women have a stronger preference for masculine faces. Little et al. (2001)
reasoned that, attractive women need not
trade-off male condition and investment as
markedly as must unattractive women; masculine men should be more likely to invest in
relationships with attractive women. Hence,
attractive women should more strongly prefer facial masculinity. Studies by Little
et al. (2001; using self-reported attractiveness) and Penton-Voak et al. [2003; using
others’ ratings of facial attractiveness and
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waist-to-hip ratios (see below)] support this
hypothesis.
Preference for masculinity varies with culture. Penton-Voak et al. (2004) proposed that
women’s preference for masculinity should
have been selected to be sensitive to cues of the
relative value of condition (and genetic benefits) and investment of male mates in their local ecologies. In Jamaica, infectious disease is
more prevalent (due to higher parasite loads
and poorer medical care) and male parental
investment less pronounced than in the
United Kingdom. They predicted and found
that Jamaican women show greater preference for facial masculinity than do British
women.
Findings that women’s preferences for facial masculinity are conditional constitute
provisional design evidence that women’s attraction to male faces have been shaped by
how male condition and parental investment
have traded-off.
Facial Averageness
In 1990, Langlois & Roggman published a
highly influential study. They digitized photographs of faces, then created composites
of sex-specific sets of them. Raters of both
sexes found the “averaged” faces to be attractive, consistent with earlier speculation
by Symons (1979) and suggestive findings by
Galton (1878). The finding has been replicated many times (e.g., Wehr et al. 2001),
including in China and Japan (e.g., Rhodes
et al. 2001a) and in the Ache (Jones & Hill
1993). This preference is not merely due to
the fact that composite faces are symmetrical
and have unblemished skin; people find average face shape and morphology attractive
(e.g., O’Toole et al. 1999, Rhodes et al. 1999,
Valentine et al. 2004). As discussed above,
some faces are more attractive than average
faces. Nonetheless, extreme departures from
average on even sexually dimorphic traits are
not attractive.
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Two main hypotheses may explain preference for averageness.
A generalized sensory bias favors prototypes.
Organisms may show preference for
stimuli that are readily processed (e.g.,
Enquist & Arak 1994). People may build up
cognitive prototypes of distinct categories
of stimuli, representations consisting of
average features, which are useful for discriminating new instances of the category.
Stimuli that match a prototype well may
then be preferred. Halberstadt & Rhodes
(2000, 2003) found that people indeed find
averaged instances not only of faces, but
also of dogs, fish, birds, wristwatches, and
automobiles, attractive. Although familiarity
of the stimuli could account for preferences
for average wristwatches and automobiles,
it could not explain preferences for dogs,
fish, or birds. They proposed that people
have a preference for averageness per se,
independent of familiarity, when judging the
attractiveness of living organisms, which may
reflect a preference for signals of quality.
Averageness reflects quality. Departures
from average may reflect the effects of genetic mutation, chromosomal abnormality,
nongenetic congenital deformation, disease,
or other factors affecting quality. Zebrowitz
& Rhodes (2004) found that facial averageness
predicted pubertal intelligence and adolescent
health (the latter for women), but only in the
lower half of the distribution. They therefore
proposed that averageness (and other purported indicators of condition, such as facial
masculinity) discriminates average from “bad”
genes (or poor condition) but not from “good”
genes. In fact, however, this effect may not be
robust, as the regression slopes for high and
low averageness groups did not significantly
differ. Moreover, a plausible alternative is that
prediction at the high end of averageness is
compromised because some nonaverage features indicative of good condition (e.g., sexually dimorphic features) are preferred. Aggregates of different signals may discriminate
condition along a continuum, a possibility to
be explored in future research.
Facial Symmetry
Bilateral asymmetry on features that, on average within a population, are symmetrical may
reflect perturbations occurring during development due to mutations, pathogens, toxins,
and other stresses (e.g., Møller 1999). Manipulations of symmetry of signals in some
(but not all) other species affect attractiveness
(see Møller & Thornhill 1998). Grammer
& Thornhill (1994) found facial asymmetry to negatively predict attractiveness.
Manipulations of symmetry generally enhance attractiveness [Rhodes et al. 1998, 1999,
2001a (including samples from China and
Japan); Perrett et al. 1999; Koehler et al. 2002;
compare Noor & Evans 2003]. [Studies manipulating symmetry by pairing left- or rightface mirror images, which look strange, have
not found this effect. See Møller & Thornhill
(1998).]
Two empirical questions arise. The first is
the size of the effect of symmetry on normal variation of attractiveness. Whereas female femininity and facial averageness reliably
account for moderate amounts of variation in
attractiveness, symmetry does not: Grammer
& Thornhill (1994), Baudouin & Tiberghein
(2004), Jones et al. (2004), Hume &
Montgomerie (2001), and Scheib et al. (1999)
report positive findings, whereas Rikowski &
Grammer (1999), R. Thornhill & S.W.
Gangestad (unpublished data), Rhodes et al.
(2001b), Shackelford & Larsen (1997),
Simmons et al. (2004), and Koehler et al.
(2004) found null or mixed results. The correlation in most populations is probably in a
predicted direction but weak (r < 0.2).
A second question concerns the extent to
which facial symmetry per se generates its
association with attractiveness. Scheib et al.
(1999) found that both facial and body asymmetry predict male facial attractiveness. But
facial symmetry predicted just as well the
attractiveness of half-faces, which possess
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minimal cues of symmetry (see also PentonVoak et al. 2001). Jaw size and prominent
cheekbones (the first a masculine trait, the
second not; see also Gangestad & Thornhill
2003a; compare Koehler et al. 2004) covaried
with symmetry and was able to account for
its association with attractiveness. Men with
symmetrical faces may have healthier looking
skin as well (Jones et al. 2004).
Perhaps ironically, it is not clear that facial
symmetry should be used as a cue of condition. Single trait asymmetries are very weak
indicators of underlying variation in developmental instability, with R or R > L differences in the population),
these asymmetries do not affect attractiveness; rather, deviations around them (atypical asymmetries) do, a finding also consistent
with either the perceptual bias account or the
symmetry-marks-quality explanation.
One finding favoring the symmetrymarks-quality explanation is that, just as
attractive women have relatively strong masculinity preferences, they have strong symmetry preferences (Little et al. 2001). At the
same time, Koehler et al. (2002) found no evidence that normally ovulating women particularly prefer symmetrical faces—as they
prefer masculine faces—when near ovulation. Zebrowitz & Rhodes (2004) found an
association of facial symmetry with childhood intelligence but not health. In sum,
we do not yet know the extent to which
it drives attractiveness judgments and, to
the extent that it does, what explains the
preference.
Female Body Form
In 1993, Singh proposed that, although preferences with respect to female body weights
vary cross-culturally, men universally prefer
women with a low waist-to-hip ratio (WHR).
Women have lower WHRs than do men,
largely due to the fact that women tend to
store fat in the hips as well as breasts, which
is selectively available for gestation and lactation. It now appears that, across a wide variety of cultures (though see below), men do
prefer a lower-than-average WHR (most preferred typically being about 0.7, compared to
a mean in most populations of about 0.75–
.80; e.g., Singh 1993, 1994a,b; Singh & Luis
1995; compare Tassinary & Hansen 1998, but
see Streeter & McBurney 2003).
The primary benefit of this preference may
ancestrally have been the same as a benefit of
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a preference for feminine faces: Low WHRs
reflect a history of energy balance and flux
that promotes allocation of energy into reproductive effort. The proximate mechanism
may involve estrogens. Indeed, Jasienska et al.
(2004) found that, within a Polish population,
women with lower WHRs and larger breasts
have greater fecundity than other women, as
assessed through precise measurements of estrodial (E2) and progesterone. Quite possibly, reproductive women’s tendency to store
fat on the hips and breasts evolved as adaptations for creating a low center of gravity appropriate for carrying fetuses and babies and
putting fat where it can readily be converted
for lactation, respectively (e.g., Pawlowski &
Grabarczyk 2003). As a correlate of fecundity,
however, it may have coevolved as a signal of
quality, with mating benefits possibly leading
to some exaggeration and display.
If facial femininity and attractive body
shapes signal overlapping qualities, one might
expect them to covary across women. PentonVoak et al. (2003) reported a significant, modest correlation between facial attractiveness
and WHR in a U.K. sample (r = −.28).
By contrast, Thornhill & Grammer (1999)
found a near-zero correlation (r = 0.013),
despite correlations between attractiveness of
distinct bodily features (e.g., face and back attractiveness). Similarly, R. Thornhill & S.W.
Gangestad (unpublished data) found little correlation (or curvilinear relationship) of female WHR with measured facial masculinity (r = −.07) or facial attractiveness (r =
−.11). Body shape and facial femininity contain largely nonredundant information; future
research should address their distinct sources
of influence.
The universality of a preference for low
WHRs has been challenged. Men in two
foraging or traditional societies have been
claimed to largely disregard WHR and generally prefer women viewed as relatively heavy:
the Matsigenka of Peru (Yu & Shepard 1998)
and the Hadza of Tanzania (Wetsman &
Marlowe 1999). Sugiyama (2004) found a similar preference for large body size in the Shi-
wiar of Ecuador. There, as in other foraging societies studied, however, women have
higher WHRs (close to 0.9 on average) than
do women in Western populations. Using
a sample of figures with variation typical
of the Shiwiar and controlling for weight,
Sugiyama found that Shiwiar men do prefer smaller WHRs. In foraging societies, female body weight may be a positive predictor of fecundity (e.g., Hill & Hurtado 1996)
and obesity may rarely be a health problem
(e.g., Brown & Konner 1987). Hence, men
may use energy status (stored body fat) as a
cue of fecundity and ability to lactate effectively. In Western cultures, energy status appears to be weakly associated with fecundity
(Ellison 2003) and hence men weight more
heavily indicators of energy balance and flux
(e.g., WHR). At the same time, they may
prefer women of moderate body mass index (BMI), argued to be a powerful predictor of female body attractiveness in Western
samples (e.g., Tovee et al. 1999, 2002).
A key unanswered question is whether and,
if so, how selection has shaped adaptations
for male preference for female body shapes
or sizes to be conditional and depend on local
ecological factors that affect predictors of female fecundity. Sugiyama (2004) has proposed
that men do have specialized adaptations for
preferring women of high fecundity (see also
Marlowe & Wetsman 2001), which have been
shaped to be sensitive to local conditions, but
the nature of such conditional inputs (e.g.,
food scarcity, distribution of body types, etc.)
remains poorly understood. Cultural transmission processes (e.g., Boyd & Richerson
1985) may also play important roles, but these
are not well understood either.
WHR: waist-to-hip
ratio
BMI: body mass
index
Male Physique
Scant research has addressed female preferences for male body features. Dixson et al.
(2003) found that women in both Britain
and Sri Lanka prefer lean, muscular (mesomorphic) body types most, followed by average and then skinny body types; heavy
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(endomorphic) body types are least preferred.
Women also prefer men with broad shoulders,
relative to waist or hip size (i.e., a “V-shaped”
torso; see also Horvath 1981, Franzoi &
Herzog 1987, Lindner et al. 1995, Mehrabian
& Blum 1997, Hughes & Gallup 2003), average WHRs (Singh 1995), and possibly chest
hair (Dixson et al. 2003). To date, these preferences have been studied in few cultures.
A number of potential benefits could explain these preferences: physical protection,
nutritional resources, and positive externalities of male status, as well as indirect genetic benefits to offspring. Women particularly prefer muscularity in men as short-term
(as opposed to long-term) partners (e.g., Buss
& Schmitt 1993), and normally ovulating
women may be particularly attracted to muscular men as short-term partners when near
ovulation (Gangestad 2004), effects consistent with muscularity functioning partly as
an indicator of genetic benefits (Frederick &
Haselton 2004). Naturally, however, direct
benefits cannot be ruled out.
One question left begging to be asked is
why women prefer masculine body traits (fostered by testosterone, which promotes muscle
growth; see Ellison 2003) but do not systematically prefer masculine facial features. Possibly, though sharing some influences, body
and facial masculinity do not signal precisely
the same traits. Future research should examine the independent influences on these traits
to address why female preferences for them
apparently differ.
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BODY MODIFICATION
To the extent that one can produce the signals that have been recurrently associated with
high mate quality throughout the history of
our species, he or she will activate, in potential mates, their psychological adaptations
for choosing suitable mates. These adaptations are vulnerable to deception, and humans have found innumerable ways of modifying their bodies to just this effect. A wide
range of methods, from the quotidian (diet
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and exercise) to the absurd (e.g., buttock implants), may be understood as techniques of
enhancing the strength of mate value signals. Men and women alike report using various techniques of appearance enhancement
for attracting and/or retaining mates (Buss &
Shackelford 1997). Practically every inch of
the body surface provides some indication of
age, health, strength, and fertility. Although
age, per se, may not be an important aspect
of quality, age cues are also cues to health
and fertility status. Substantial cross-cultural
variation in the size of the sex difference
notwithstanding, men throughout the world
are more concerned with women’s physical attractiveness than vice versa, and women who
look relatively young are consistently rated as
attractive (Buss 1989, Jones 1995).
Among the ways people’s faces reliably
change with age are decreases in the visible area of the eyes and the red area of the
lips and an increase in the size of the nose
( Jones 1995). Duncan & Collison (2003) report that extracts from the toxic Atropa belladonna (deadly night shade) were first used
for pupillary dilation to enhance eye appearance over 2000 years ago. Today botulinum
toxin is used for a number of cosmetic purposes, including lifting the eyelids. Blepharoplasty (eyelid surgery) is the third most popular cosmetic surgery in the United States
(Meisler et al. 2000). Slightly less popular,
but nonetheless routine, procedures include
rhinoplasty and collagen lip injections. To
some extent, a more youthful facial appearance can be achieved through makeup, but
over a million cosmetic surgeries were performed in the United States alone in 1998, and
the number is expected to rise in the coming
decades (Meisler et al. 2000).
The color, luster, and volume of hair all
indicate age and health. The hair of younger
women is judged to be of higher quality
than that of older women, and it is primarily
younger women who choose to wear their hair
long (Hinsz et al. 2001). Hair growth tonics
of varying efficacy have for hundreds of years
been successfully marketed to men concerned
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with hair loss. Laser follicular stimulation and
countless dietary supplements are purported
to reverse or slow hair loss. Hair implants
(plugs), toupees, strategic combing, and in a
sense, shaving, are also popular ways to cover
the problem. For those men and women who
have no shortage of hair, but are unhappy
with its appearance, the number of products
to clean, condition, or color the hair defies a
thorough cataloguing.
Tiggemann & Kenyon (1998) describe a
youthful feminine look as including a slim
body, high taut breasts, and smooth hairless skin. Dieting, exercise programs, weight
loss surgeries and medications, breast augmentation and reduction surgeries, liposuction, electrolysis, and shaving can be variously
mixed and matched to achieve such an appearance. Removal of body hair by women in many
societies is so widespread as to go unnoticed,
except by its omission. A survey of female Australian students (Tiggemann & Kenyon 1998)
showed that over 99% of female college students in the sample had shaved their leg or
underarm hair at some point, and about 92%
of the full sample, including high school students, regularly shave their leg and/or underarm hair. The number one reason given by
college students was, “It makes me feel attractive,” and of high school students, “Body hair
is ugly.” This is a historically novel position,
at least among people of European descent (as
most of this sample was), but clearly the idea
has gained great popularity.
By the year 2000, more than million
women in the United States had either silicone or saline breast implants, but riskier
forms of breast implants have been documented from the eighteenth century and
primitive brassieres from as early as 5000 years
ago (Sarwer et al. 2000). Sarwer et al. estimate the average age of breast augmentation patients to be 31 years and conclude that
the weight of the evidence supports improvements in “body image, quality of life, and (a
reduction in) depressive symptoms” following
cosmetic surgery. Although the ideal breast
size varies by culture and period, the authors
declare that “large breast size has been more
or less in vogue since antiquity” (Sarwer et al.
2000).
Body sculpting, not weight reduction, is
the primary purpose of liposuction (Meisler
et al. 2000). Corsets, girdles, and other sculpting undergarments have been used to give the
appearance of a slender waist (but not hips) for
hundreds of years. These facts are consistent
with Singh’s (1994b) evidence that a low waistto-hip ratio is a better predictor of women’s
attractiveness than is thinness. Interestingly,
however, in a U.S. sample, thinness itself is so
highly valued that 24% of women and 17%
of men “would surrender three years of their
lives to be thinner” (Alam & Dover 2001).
Breast augmentation patients, compared
to controls, report greater health and greater
investment in fitness and health, and also report higher rates of having been teased about
their appearance in adolescence (Sarwer et al.
2003). A recent review of the psychological
and psychosocial results of cosmetic surgery
procedures (Honigman et al. 2004) found
high satisfaction among recipients of breast
reduction and augmentation procedures visà-vis self-esteem, confidence, attractiveness,
and body image, but something of a mixed bag
among recipients of facial surgeries. A number of these people reported being shocked
by their new appearance and feeling a loss
of identity, an understandable outcome for
anyone suddenly confronted with a new face
(attractive or otherwise) in the mirror.
CURRENT AND FUTURE
DIRECTIONS
Tremendous progress toward an understanding of human physical beauty has been made
over the past decade and a half. Prior to that
time, the literature offered at best rudimentary understandings of the extent of crosscultural agreement on physical attractiveness
(as well as precise domains of variable beauty
standards) or of the impact of specific physical features. Much of our current understanding is owing to evolutionary thinking,
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as many lines of research were motivated by
hypotheses derived from explicit selectionist
theory.
Despite this progress, the next 15 years
may produce even greater gains. Key questions beg to be answered. Fundamental issues
remain unresolved. Some have yet to be seriously addressed. We discuss five crucial topics
for future research.
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The Precise Benefits Generating
Preferences
We have stressed this topic throughout our
discussion. Though researchers have surely
not ignored it, in few instances can we draw
firm conclusions. Questions remain about the
signal value of facial averageness, symmetry, male muscularity, and even sexually dimorphic facial features. Very little is known
about the underlying fitness correlates of preferred traits in traditional settings (e.g., do
estrodial profiles covary with facial femininity?). In most cases, even less is known about
the precise proximate mechanisms that generate them and the factors to which they
are sensitive (e.g., does mutation load or
pathogen resistance affect facial averageness,
symmetry, or the development of sexually
dimorphic features?). Both issues are relevant to design arguments pinpointing the
ultimate causes of signaling systems (e.g.,
Kokko et al. 2003). From an evolutionary perspective, this topic is a fundamental
one. Fortunately, adaptationist theory offers a
rich array of hypotheses about potential benefits to generate fruitful research programs.
The Overlapping and Independent
Contributions of Preferred Features
Both men and women are attracted to arrays of features. Different features may signal the same underlying beneficial trait (“quality”; e.g., Thornhill & Grammer 1999), each
an imperfect indicator of it (Fink & PentonVoak 2002). Alternatively, multiple preferences may have evolved because different
540
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·
Scheyd
traits signal different preferred qualities (or
resulted from unique sensory biases). Although the former view might suggest that
all preferred features should covary, in fact
positive, negative, or zero correlations between multiple indicators of the same trait
may evolve (Kokko et al. 2003). As with the
previous question, answers to this question
may require an understanding of the precise fitness correlates and underlying developmental and proximate influences of preferred
traits.
The Integration of Different Signals
Whether different features signal the same
quality or different underlying qualities, the
question of how individuals have been shaped
to integrate them arises. Do sexually dimorphic features, averageness, and facial
symmetry affect attractiveness additively or
multiplicatively—and if the latter, in what
manner? Dixson et al. (2003) found that if
a male is heavy (endomorphic), variations in
WHR or shoulder-to-waist ratio have little
impact on his attractiveness; he is seen as relatively unattractive regardless. Among muscular men, however, variations in WHR and
shoulder-to-waist ratio considerably affect attractiveness, as the ideal male body type is a
restricted mesomorphic type. More generally,
however, we have little grasp of these interactions and even less appreciation of how signal
integration may have been shaped by selective
forces.
The Conditional Nature of
Preferences
As noted repeatedly throughout this chapter,
preferences may be shaped by selection to
be conditional: to depend on particular circumstances that modulate the value of attraction to specific features. This theme is one
that has driven a number of recent research
programs and should continue to do so. At
least four types of condition-dependent preferences have been conjectured.
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Calibration of preferences to local ecological and socio-ecological conditions. Despite substantial cross-cultural convergence
with respect to standards of beauty such
as female facial femininity and averageness,
some preferences vary cross-culturally (e.g.,
female preferences for male facial masculinity, male preferences for female body fat).
Do these variations reflect adaptations sensitive to specific ecological inputs that ancestrally affected the value of particular features (e.g., disease prevalence in relation
to male facial masculinity; food scarcity in
relation to female body mass)? To what
to extent are these variations nonadaptive
and maintained through cultural transmission
processes?
Calibration of preferences to individual
variations within culture.
Different individuals may differentially benefit from pursuing particular individuals as mates. Just as
Little et al. (2001) proposed that attractive
women should have a stronger preference for
facial masculinity, Johnston et al. (2001) argued that sex-typed, feminine women should
particularly favor male masculinity and Brase
& Walker (2004) hypothesized that attractive men should particularly value women
with low, attractive WHRs. More generally,
Scheyd (2004) proposed and found evidence
that men’s own attractiveness affects their
weighting of features that are consensually
considered attractive; in three different samples (including one from a rural village in
Dominica, West Indies), unattractive men,
relative to attractive men, were less drawn
to those women found to be most attractive overall. Researchers have also speculated
that men differentially disposed to long-term
and short-term mating should be differentially attracted to signals of RV (youth) and
current fecundity, respectively. Nonetheless,
individual differences in weighting or integration of signals affecting attractiveness have
barely been addressed. Adaptationist theories clearly speak to them, however; individual differences may be a key testing ground
of adaptationist hypotheses about special
design.
Preferences vary as a function of relationship context.
What may be most attractive in a long-term mate may not be what
is most attractive in a short-term mate. Researchers have explored and found differences
in standards of attraction across relationship
contexts. Most work to date, however, has
used self-report measures of preferences (e.g.,
Buss & Schmitt 1993). None has been done in
traditional societies.
Preferences vary as a function of individual circumstances.
Until the late 1990s,
no one reading the literature would have suspected that women’s standards of attraction
change across their ovulatory cycles. Owing to specific adaptationist hypotheses, we
now know that they change in many ways.
What other immediate life circumstances
(e.g., pregnancy, mating status, parental status, etc.) affect standards of attraction in ways
predicted by adaptationist hypotheses?
The Moderating Effect of
“Non-Physical” (or Nonstatic)
Features
Attractiveness research often assumes, at
least implicitly, that people’s attractiveness
is judged on the basis of static cues, independent of other information about them.
Except in attractiveness research and the
print media, however, people’s attractiveness
is rarely if ever judged on the basis of static
representations (photographs). And in traditional human societies, people typically have
much information about others to whom they
may or may not be attracted. Riggio et al.
(1991) found that, although static facial attractiveness strongly predicts attractiveness in a
situation in which observers see faces dynamically change, dynamic features also have important effects. And information garnered as a
result of repeated interaction with others can
change perceptions of individuals’ physical
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attractiveness, favorably or unfavorably (Kniffin & Wilson 2004). Adaptationist theories
may speak to these effects (e.g., see Gangestad
et al. 2004, for evidence that women’s attraction to dynamic information changes across
their cycles).
SUMMARY
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We have presented a more-than-skin-deep
look at the evolution of physical attractiveness. To summarize in one chapter a signaling
system constructed by the mating choices of
billions of our ancestors is a challenging task.
Nonetheless, we have endeavored to explain
how these choices have shaped the preferences
and choices of present-day humans. We have
presented our perspective on the nature of signaling systems generally and argued that the
display and perception of human physical attractiveness form one such system. The details
of this particular system are only now coming to light, but the importance of sexual dimorphism and averageness in attractiveness,
and of one’s own attractiveness or ovulatory
state in judging it, are but a few examples of
the broad range of fascinating work currently
coming out of the field.
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