7 Biology
7.1 Explanatory framework
The biological view of the family is based on evolution and the implications of natural selection for human behaviour. It includes evolutionary psychology, which focuses on the development of the human mind, human behavioural ecology, which traces linkages between ecological factors and behaviour, memetics, the idea that culture evolves, and dual transmission theory, which views cultures and genes as co-evolving in separate but linked systems of inheritance, variation and fitness (Laland and Brown 2002, Smith 2000b).
All these approaches to the evolutionary analysis of human behaviour are complementary and have at their core the idea that human behaviour is biologically driven and derived from genetic selection that conferred adaptive advantages in the prehistoric past. It postulates that over generations, humans encountered obstacles to genetic success, and that selection favoured those with brains suited to overcoming these problems (Alcock 2001). Yet while the human brain is the product of evolution, the human condition has changed immeasurably over time.
Since most of human evolution occurred in the Pleistocene on the African savannah, and modern environments are too recent to have permitted rapid evolutionary change among humans, evolutionary approaches look to the prehistoric and not the modern environment for adaptive explanations. The hypotheses generated by the approach are typically tested in environments that are surmised to resemble the prehistoric context—contemporary pre-industrial societies.
Evolutionary biologists consider that some human traits are universal, that they are likely to have genetic causes and that it should be possible to find evolutionary explanations for them (Morris 2001). The evolutionary approach tries to explain ubiquitous behavioural inclinations in terms of their adaptive functions ie, to explain how they could contribute to fitness. It is not easy to determine what complex physical and mental traits were adaptations. An adaptive trait is one that directly or indirectly promoted reproductive success when it originated. But not all traits are adaptive—some may be accidental or simply be by-products of adaptations rather than adaptations themselves.
Evolutionary theory suggests that there are real differences between men and women that developed in the past to enhance survival in past environments. Choosing a partner, achieving and assessing status, cementing relationships and identifying offspring as their own are recurrent adaptive problems faced in human evolutionary history. Individuals who best solved these problems left more descendants than the less well fitted. The differences between men and women, consequence of the human system of reproduction, mean that humans carry genetic predispositions that may not confer an evolutionary advantage in today’s world.
A core idea of the evolutionary approach is that almost all the main differences between males and females stem from differences in their investment in offspring (Trivers 1985). Females start with a bigger investment (the egg) and make further investment in feeding and caring for infants. Males make a smaller investment, contributing sperm and become devoted fathers when the benefits exceed the costs—when the offspring need his care; are easy to protect and when he can provide for them (Pinker 1998). Females thus produce few, large, expensive eggs, while males produce many small cheap sperm. The return on effort is different, too. While there may be a high fixed cost for males in establishing status and acquiring resources that procure access to females, the marginal cost of each additional offspring is low. For females, each additional offspring requires about as much resources as the first as there are few economies of scale in childbirth.
Since each offspring needs an egg and sperm, the number of eggs the female can produce and nurture limits their number. A single male can fertilise many females, creating competition between males for females. On the other hand the reproductive success of females does not depend on how many males they mate with, but on choosing the “best” male. The level of parental investment leads the greater-investing sex to choose and the lesser-investing sex to compete to be chosen.
Evolutionary theory therefore predicts that because men and men have different levels of investment in children, leading to different evolved psychologies, their priorities and behaviours are not identical. These differences have profound consequences for how individuals make decisions and how they behave within families.
7.2 Family formation
Evolutionary theory suggests that the relative investments of men and women in children mean that they have different mating strategies that can have profound implications for the formation of families. Since there is little or no male parental investment in most mammalian species, female mammals typically chose mates on indicators of their genetic quality such as strength, size and aggressiveness. However, human infants are helpless and need intensive and prolonged parental investment—more than the mother alone can provide. Sexual selection is thus likely to have favoured human males able to provide extra investment and females who choose males not only on indicators of their genetic fitness, but also on their ability to provide parental investment (Chisholm 1999). Males compete not only for the role of mate, but also for the role of father—the ability and willingness to provide resources to raise children that will pass on their genes. Women select males with the ability to invest in their offspring, as demonstrated by their age, wealth and status. Women who marry successful older men are likely to leave more descendants than those who marry younger unproven men.
The theory suggests that men have thus developed a predisposition to seek status, for example through hunting prowess, or the acquisition of wealth, that signals to prospective mates their ability to provide for children. This tendency includes competing with other males for domination. Competitive risk-taking and social display (showing off) are likely to be an evolved male trait to honestly signal personal qualities (Zahavi 1977). Successful risk-taking is accorded generalised prestige and status, based on an implicit assumption that it reflects enduring personal qualities that will ensure ongoing success in other endeavours. The respect of peers is a major determinant of social status, and the respect that status affords reduces the likelihood of challenges from other men and increases attractiveness to women (Winterhalder and Smith 2000). The risky competitive inclinations of men are manifested in various ways, from fast cars, to sports, gambling, drug taking and work, as well as in direct confrontations, often involving the threat of or actual violence, with other men.
A key insight of the evolutionary approach is that low-status men who face reproductive failure (in contemporary society typically unemployed, disadvantaged, single and young) compete most strongly for access to women and have the least to lose in conflicts with one another. Young single adult males, with few resources and poor prospects are most likely to engage in risk-taking behaviours and in dangerous, competitive altercations with other men—this has been termed the “young male syndrome” (Wilson and Daly 1985). Men who lack demonstrable status and wealth that could induce women to choose them may fall back on coercion—the threat or use of force—of women to have sex with them (rape), of others to give up resources (robbery) and of other males to give them power and respect (aggression, violence and risk-taking behaviour) (Chisholm 1999). These predispositions are likely to be have been adaptive—men exhibiting them are likely to have left more descendents carrying these genes than those in similar circumstances who did not.
Buss (1994) identified that differences in the taste for mates is universal among men and women. For example. men typically seek women who are young and beautiful, whereas women seek men who are older and wealthier. Evolutionary theory suggests that a man’s reproductive success depends on the fertility of a wife, and the younger the wife, the more children she can bear and rear, so men have developed a taste for nubile women (Buss 1994). Younger women are also unlikely to have children fathered by other men. Female beauty reflects a woman’s reproductive virtues, including health, youthfulness and not having been pregnant, and acts as a signal of genetic fitness (Symons 1995). Women try to make themselves more beautiful to increase their ability to compete for husbands.
These preferences have been confirmed (and replicated elsewhere) in a study of people in 37 countries, which showed that people everywhere value intelligence, kindness and understanding most highly, but that men and women differ in the other qualities they seek in a mate (Buss 1994). Women value earning capacity, status, ambition and industriousness in a man, while men value youth and beauty. Women prefer older men, while men prefer younger women. As a result, older, prestigious men can attract young and beautiful women. At the same time, very successful, high status women prefer men who are even more successful. The standing of men relative to women is important—women everywhere prefer to marry men of higher status than themselves (Buss 1994). They find cues to men’s status attractive, and men, in turn signal their status to women. Women’s preferences mean that they trade off physical attractiveness of men for resources in seeking long-term partners (Gangestad and Simpson 2000, Waynforth 2001). People tend to find marriage partners they see most often and that are most like them in terms of intelligence, status and appearance (Buss 1994). This assortative mating tends to reinforce characteristics and reduce variability in a population.
