Social Psychology Attractiveness and evolution Christopher Hand Department of Psychology University of Glasgow July 2006
Darwin and evolution Charles Robert Darwin (1809-1882) 1859 – publishes On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life (usually abbreviated to ‘The Origin of Species’)
The biological roots of social behaviour • Darwin identified that within each species, there are variations from one individual to the next. • Many of these variations are a function of the species’ genetic make-up • Inherited by their descendants
The biological roots of social behaviour • However – • This inheritance will happen only if the animal actually has descendants! • Most organisms do not live long enough to reproduce. • The issues of who survives and who reproduces are far from random…
The biological roots of social behaviour • A process of selection, if repeated generation after generation, would produce large changes in a species. • Therefore, a survival advantage for a genetically-rooted trait will lead, over the generations, to a change in the entire species.
The biological roots of social behaviour • Not all variations within a species are beneficial in this way. • Not all variations lead to a reproductive advantage. • Evolution should not be thought of as favouring the “better” or “more advanced” organism…
The biological roots of social behaviour • Instead – • Evolution merely favours the organism that is better suited to the environment currently in place. • If the the environment changes, then the pattern of selective advantages will change as well.
Personal and genetic survival • “Survival of the fittest” • Misleading • Personal survival matters insofar as that survival leads to reproductive success • Pass on genes to next generation
Personal and genetic survival • An animal that outlives its competitors, but leaves no offspring, has not flourished. • Thus, what really matters for evolution is not personal survival, but the survival of one’s genes. • It is via one’s genes that future generations (and so the evolution of the species) will be shaped.
Behaviours rooted in genes • Many behaviours are rooted in an animal’s genetic makeup • these too are inherited by their offspring. • If these behaviours contribute to reproductive success – • animals with these behaviours will have more offspring • a larger proportion of the next generation will inherit the genes that led to the behaviour in the first place
Behaviours rooted in genes • In this fashion, natural selection will lead to an evolution of how animals behave just as it leads to an evolution of the animal’s anatomy
Social behaviour and reproduction • What behaviours are most likely to be shaped by evolution in this way? • Social behaviours • Particularly those associated with the process central to evolution • Reproduction
Advertising for a mate • First things first • Find a mate! • Requires the animal to advertise their availability and their sex • So that males are noticed by females and vice versa • Many animals have anatomical structures whose function seems to be nothing other than this sexual advertising…
Andersson (1982) Male widow birds have long tailfeathers, up to 20 inches long. The tails of some males were cut, and extensions were placed on the tails of others. Males whose tails were cosmetically enhanced had more nests than unaltered males, who in turn had more nests than males with shortened tails.
Advertising for a mate • In humans, structural displays of sex differences are less pronounced. • Jordan is the exception to the rule. • According to some theorists, the female breast evolved for signalling purposes • As we began to walk erect and lose our reliance on smell, members of our species needed some other ways of displaying their sex.
Behavioural advertisements • Many animals advertise both their sex and their readiness to mate via their behaviours. • Courtship rituals • Sometimes elaborate, involving alternating bouts of approach and withdrawal, coy retreat and seductive flirtation. • Why this alternation between ‘yes’ and ‘no’?
Behavioural advertisements • Each animal has reason to approach the other, • But, each also has reason to fear the other • Is the approach amorous or aggressive? • This tension between attraction and threat must be resolved • Alternating approaches and withdrawals presumably serve this purpose.
Attraction • Humans are biological creatures • Our behaviours perhaps including aspects of courtship might well be shaped by our genes. • On the other hand • Culture-based learning during our lifetime may play a larger role in determining when, how and whom we mate.
Attraction • There is no question that culture does have an influence. • It is cultural change, not ultrarapid evolution that has altered the average age of parenting over the last few decades. • It is cultural differences, not biological contrast that made people with facial tattoos attractive among New Zealand Maori but not to many Westerners
Attraction • What commonalities are there among the diverse peoples of the world with regard to mate preferences and courtship patterns? • No commonality • Powerful argument that human mating is not heavily governed by biology. • Commonality • Is it this part of our biological heritage?
Physical Attractiveness • Physical appearance is immensely important in determining a person’s attractiveness • Or at least their initial attractiveness. • US demand for cosmetic and toiletry chemicals is forecast to rise 5.4 percent per year to $7.6 billion in 2010 • At least £255 million spent in UK in 2005 on cosmetic surgery procedures
Walster, Aronson, Abrahams, & Rottman (1966) • College freshmen were randomly paired at a dance and later how much they liked their partner and whether he or she was someone they might want to date. • The main determinant of each person’s desirability as a future date was their physical attractiveness.
Green, Buchanan, & Heuer (1984) • Studied clients of a video-dating service who selected partners based on files that included a photograph, background information, and details about interests, hobbies and personal ideals. • When it came down to actual choice, the primary determinant was the photograph.
Physical Attractiveness • Physically attractive individuals also benefit from the common belief that what is beautiful is good. • People tend to associate physical attractiveness with a variety of positive personality traits • Dominance • Good social skills • Intelligence • Happiness • Good mental health • Dion, Bersheid, & Walster, 1972
Physical Attractiveness • Attractive people are: • Judged as less maladjusted or disturbed (Cash et al., 1977; Dion, 1972) • Judged as more likely to be hired after a job interview (Dipboye et al., 1977) • Rated as happier, more successful, having a better personality and more likely to get married (Dion et al., 1972) • Given an easier time by jurors, if the defendant was female (Sigall & Ostrove, 1975) • Evaluated more highly on their written work, if they were female students (Landy & Sigall, 1974)
Physical Attractiveness • People often assume that individuals who are more attractive will also be more intelligent than average. • In truth, there is no correlation between attractiveness and intelligence • Eagly, Ashmore, Makhijani, & Longo, 1991; Feingold, 1992; Jackson, Hunter, & Hodge, 1995.
Matching for attractiveness • Physical attractiveness is clearly desireable • But if we set our sights on only the most desireable, the world would soon be depopulated • There aren’t enough supermodels to go around : ( • We seek partners who are roughly the same level of attractiveness that we are • This will ensure that we reach as high as we can, while simultaneously minimising the chance of rejection.
Matching for attractiveness • Much evidence favours this matching hypothesis • There will be a strong correlation between the physical attractiveness of the two partners • Berscheid, Dion, Walster, & Walster, 1971 • Everyday observations confirm this hypothesis • “They make such a good couple” etc • As do many empirical studies • Berscheid & Walster, 1974; Feingold, 1988; White, 1980.
What is physically attractive? • To some extent, this is a matter of personal taste • “Beauty is in the eye of the beholder” • However, there is more agreement about attractiveness than this bit of common wisdom would suggest.
What is physically attractive? • People of different cultures, by and large, seem to agree about which faces are attractive, as do people of different generations • Cunningham, Roberts, Barbee, Druen, & Wu, 1998. • Evidence also indicates that infants prefer to look at faces that adults consider attractive, suggesting that the allure of faces is not learned • Langlois et al., 1987.
What is physically attractive? • Across ages, generations and cultures, attractive people are almost always those with: • Clear skin • Shiny hair • No visible deformities
What is physically attractive? • Faces that are symmetrical are usually considered more attractive than those that are not. • Generally, “average faces” (those of average width, eye size, and so on) are more attractive than faces that deviate from average • Grammer & Thornhill, 1994; Fink & Penton-Voak, 2002; Mealey et al., 1999; Rhodes et al., 1998; Rhodes et al., 1999; Thornhill & Gagestad, 1999.
What is physically attractive? • However, some departures from average increase attractiveness • These seem to be the ones that exaggerate important features found in the average face. • The average female has big eyes, full lips, and a small chin • A female face will be more attractive if it has slightly larger than average eyes, fuller than average lips, and so on…
What is physically attractive? • The average male face has a strong chin, a large jaw, and prominent brows. • Therefore, a male face will be more attractive if these features are slightly exaggerated.
What is physically attractive? • As with faces, symmetry and being near average contribute to the attractiveness of someone’s body. • This is probably why individuals who are symmetrical in the size of their hands and feet begin to have sex at an earlier age and have more sexual partners in their lifetime • Thornhill & Gangestad, 1994.
What is physically attractive? • Body size • Seems to be an area where preferences vary between cultures and time periods. • Even so, there may be consistency in preferred proportions. • Waist-to-hip ratio • Waist circumference divided by hip circumference.
What is physically attractive? • Numerous studies indicate that women are perceived to be more attractive if their ratio is approximately 7:10. • Therefore, if a culture favours slender women, someone with a 241/2 inch waist and 35 inch hips will be considered attractive. • If a culture favours larger women, then someone with a 32 inch waist and 46 inch hips might be ideal. • In both cases, the 7:10 ratio is preserved • Furnham et al., 1997; Henss, 2000; Singh, 1993; Singh & Luis, 1995.
The biological basis for attractiveness • Why symmetrical faces and a certain hip-to-waist ratio? • Evolutionary explanation is that the 7:10 waist-to-hip ratio indicates mature pelvis and adequate supply of fat • Readiness for pregnancy, signals fertile partner • Relatively low ratio indicates higher oestrogen levels = better overall health and greater fertility • Singh 1993; 1994. • Any male with a preference for this shape maximises his chances for reproductive success • Natural selection favours individuals with this preference.