7.6 Family pathology
Although the evolutionary explanations of behaviour are postulated to be adaptive responses to challenges in Pleistocene environments, those behaviours are not necessarily beneficial in modern society. Indeed, some behaviours, such as aggression, violence and sexual coercion are seen as socially harmful and thus undesirable and are therefore controlled by social norms and laws. At the same time, while individuals may have these predispositions, they have the capacity for self-control and the ability to change their behaviour to suit different environments. This ability in itself is likely to have been adaptive, allowing people to adopt different strategies to maximise their reproductive fitness in different situations. The tension between predisposition and self control provides insights that can be useful not only in understanding the underlying reasons for certain types of undesirable behaviour, but also in devising effective policies to limit them.
7.6.1 Aggression and violence
Violence and aggression are likely to have been behaviours that promoted reproductive success in the distant past—simply put, individuals who were prepared to be violent or aggressive left more descendants than those who did not. However, these behaviours may not confer such benefits in the modern world, and their effects on others make then socially unacceptable.
Infanticide, for example, may be an evolved behaviour, an adaptive way for mothers to resolve the problem of rearing an infant in unfavourable circumstances or when it is unlikely to survive. In modern Western societies for instance, young, poor and unmarried mothers are at higher risk of committing infanticide (Pinker 1998). The incidence of Sudden Infant Death Syndrome (SIDS) may include a proportion of deaths by infanticide. The emotions of mothers may have been shaped by the necessity of the decision to let a newborn baby live or die. Postnatal depression seems to be most severe in circumstances correlated with infanticide such as poverty, marital conflict and sole motherhood. The gradual process “bonding” with a newborn baby may play a part.
Male sexual jealousy and aggression towards unfaithful wives or girlfriends and their lovers is likely to reflect the different genetic consequences of infidelity by men and women. It is the biggest cause of domestic violence and homicide, generally by men (Pinker 1998). The differential effects of infidelity are reflected in the lesser punishments for men who kill their adulterous wives and their lovers in “crimes of passion”. Women are typically only violent towards their husbands in self-defence or after years of abuse.
Male aggression is a “high stakes, high risk” activity that is postulated to be an evolutionary adaptation to competing for a scarce resource—female reproductive capacity. Males engage in dangerous behaviour and risky confrontations where the reward is increased status and respect (Wilson and Daly 1985). Men have powerful motives to compete for status, since women select mates on signals of status that reflect genetic superiority (Buss 1994). Rivalry between men results in arguments, insults, fights and murder—duels are a formalised example. Being male is the biggest risk factor for violence—and men kill 26 times more often than women (Daly and Wilson 1988). Men and boys are also more aggressive and more frequently aggressive than women and girls. The fiercest rivalry is typically among low status males whose prospects of attracting women are low. Young, poor men with nothing to lose discount the future steeply and are reckless (driving too fast, taking drugs, committing crimes, for example) in defending their reputations (Rogers 1994).
Among hunter-gatherer societies, war allows men greater access to women, both from the conquered group, and as being a warrior confers status, from their own group (Pinker 1998). The genetic payoff may have allowed the evolution of a willingness to fight. Brownmiller (1975) suggests that while modern warfare differs, it is similar in that soldiers abduct and rape women. In contrast, women’s reproductive success is not increased by warfare that adds available males and involves a risk of death. Evolutionary theory suggests that it is not surprising that women have not evolved an appetite for warfare.
In evolutionary terms, females have little to gain and much to lose from aggression, and are less aggressive than men. The need to care for infants (whom they are sure carry their genes) makes women concerned about staying alive and adopt low-risk strategies in conflicts. Females exhibit greater concern for their own survival than males and display more fear than males. Female aggression is likely to occur around scarce resources (necessary for her survival and that of her offspring) rather than status, and to be low-key and indirect (Campbell 1999).
When violence and homicide in families does occur, it is typically not directed against blood relatives, but against spouses, in-laws and step-relatives. The risk of being killed by a non-relative is at least 11 times higher than being killed by a blood-relative, even focusing on people who live together (Pinker 1998). Conflict among blood kin occurs less often and is resolved without killing more often, than among non-kin. Reciprocity between kin is part of conflict resolution.
7.6.2 Sexual coercion
Evolutionary theory suggests that sexual coercion may be an obvious mechanism by which men (who are bigger and more powerful than women) can enhance their reproductive success. Nonconsensual sexual intercourse (for example in rape or incest) may thus have an adaptive explanation, but different genetic payoffs for the males and females involved.
Incest avoidance is universal. Because close relatives share genes, mating increases the risk that defective recessive genes will result in compromised offspring. Natural selection will favour individuals who do not mate with close relatives (Thornhill 1991).
The evolutionary explanation for incest avoidance is that people have evolved emotions that make mating with a close relative repugnant, since they cannot directly determine relatedness (Pinker 1998). Children that are reared together, even if they are unrelated, do not tend to marry or mate. The most commonly cited example is that of Israeli kibbutzim, where unrelated children were reared communally but when sexually mature did not pair up. In another example, in Taiwan infant girls were brought up in the families of their future husbands, but the eventual marriages were typically infertile and unhappy. People become sexually averse to people they grow up with—closeness in the early years induces perceptions of kinship that negate sexual desire. People who do commit incest have often been reared apart. Fathers who sexually abuse their daughters may not have had much contact with them as small children.
The evolutionary explanation for differing emotions towards incest is that different incestuous pairings have different genetic costs and benefits for the parties (Tooby 1976a, b). Mother-son incest is rare, since there is no genetic advantage to either, and men in any case are not generally attracted to older women. For daughters and sisters pregnancy would be potentially very costly and repugnance strong—precluding other opportunities for pregnancy and involving years of breastfeeding and the possibility that the child will be deformed and require additional and long term care. Mothers get no genetic benefit and suffer the costs of defective grandchildren, and so oppose incest between the daughters and fathers or sons. For fathers and brothers, mating with a daughter or sister can increase the number of offspring sired, even if there is a genetic cost—the risk that the child will be compromised. Also, the father may not be certain that the daughter is his, reducing aversion to incest. For step-fathers and step-brothers there is no genetic cost. Most reported cases of incest are between step-fathers and step-daughters and most of the rest between fathers and daughters (Pinker 1998). In virtually all cases, daughters are coerced.
Thornhill and Palmer (2000) argue that rape arises from men’s evolved preference for a large number of mates in an environment where women choose their mates. The evolutionary hypotheses for rape are (1) that rape is a by-product of male evolutionary adaptation for multiple sex partners and (2) that rape itself is an adaptation. They conclude that although existing evidence is insufficient to determine which hypothesis is correct, it is clear that rape is centred in men’s evolved sexuality. As discussed below, this conclusion has been subject to criticism by feminists who argue that rape is about control. Thornhill and Palmer also suggest that the severe emotional and psychological responses of women who are raped may be an adaptive response to the differential genetic consequences of rape for women.
7.7 The changing family
The crucial lesson of the evolutionary approach is that our prehistoric past shaped behaviour in ways that strongly influence us today. However, today’s environment is vastly different from the Pleistocene. These changes include greater population density and larger communities, more anonymity and a less egalitarian society.
Behaviours that might have conferred adaptive advantages in the evolutionary past may no longer be appropriate in modern society, and may indeed be seen as pathological. Nevertheless, the underlying drivers of such behaviours remain. However, although the underlying forces underlying these behaviours can be explained, they cannot be justified. The human brain has adapted to be able to adjust behaviour to different circumstances. Behaviour is therefore not biologically determined—although there may be predispositions towards certain behaviours, those predispositions can be controlled.
7.8 Critiques
The evolutionary thinking about human behaviour that emerged in the 1970s was attacked vigorously, by social scientists in particular. The principal grounds were that it was simplistic and prejudicial. Adaptive explanations were dismissed as "just-so stories” and post hoc rationalisations. Evolutionary biologists, however, counter that the natural selection is the principal explanation for the design of adaptive traits. Cosmides and Tooby (1992) defend adaptationist thinking by pointing out that theories in evolutionary psychology have revealed previously unknown facts and reminding critics that questions about the function of a given structure of organs have been the basis for every advance in physiology.
While both the economic and evolutionary approaches to the family involve postulates about human behaviour it is recognised that economic explanations of how people behave may not necessarily be true, and that they are only useful if they can predict human behaviour. In contrast, adaptationist explanations in the evolutionary biology literature are often presented as if they were indeed true. However, the theories produced by evolutionary thinking, like economics, should be assessed in terms of their predictive usefulness.
Sociobiologists also were accused of abusing science to reinforce undesirable values, and critics dismissed their views on the grounds that they could be used to justify oppression by encouraging racism, sexism, elitism and imperialism (Irons and Cronk 2000). However, perhaps in response to this criticism, modern evolutionary theory emphasises that no argument about the nature of behaviour can be used as a justification of that behaviour.
Nor are evolutionary explanations equated with a deterministic view of human behaviour. While they can predict tendencies, it cannot predict how a particular individual will behave. They do not imply that there is a single gene that is responsible for a particular aspect of behaviour. Nor does it mean that behaviour is wholly determined by genetic influences, but that a range of environmental influences plays a part in development and behavioural choices.
Wilson (1978) postulated that genetic diversity underlies differences between cultures This was one of the most controversial aspects of socio-biology and was heavily criticised. Modern approaches however, concur that culture can evolve without genetic change and that individuals from different cultures can acquire cultural traits with ease. Human behavioural ecologists emphasise that culture is an evoked behavioural adaptation while evolutionary psychologists emphasise the common human nature that underlie cultural universals (Buss 2001, Laland and Brown 2002, Tooby and Cosmides 1992).
The most recent topic to evoke strong criticism is the adaptive explanation of rape by Thornhill and Palmer (2000). The idea that rape is genetic is one that critics found objectionable, running counter to the prevailing feminist theory that rape is a crime of violence against women, and not sexual. However, evolutionary biologists counter that understanding the genetic basis of rape could help to reduce it and the adaptive harm that it imposes on victims (Alcock 2001).
Darwin’s theory of evolution is widely accepted among biologists. However, it is not a single idea, and biologists can and do disagree on many of the details while agreeing that natural selection is the main cause of evolution. The principal debate is between Dawkins and Gould. Both sides agree on the fundamental idea of evolutionary change—adaptive modification through natural selection. They agree that all life, including human life, has evolved from one or a few ancestors. They also agree that the process has been natural rather than divine and that chance plays a large part in evolution. They agree that natural selection matters and that life forms more suited to an environment will tend to survive and transmit their genes to descendants. They also agree that complex capacities, like vision, evolved by natural selection and that human evolution works slowly. They agree that natural selection works by cumulative selection and single-step changes must be very rare (Sterelny and Turney 2001).
The debates are detailed and at times acrimonious, but the principal criticism by Gould seems to be that evolutionary biologists such as Dawkins see everything as a result of adaptation and competition between genes and do not recognise the existence of multiple forces in evolution and selection at different levels (Segerstråle 2000). The debates are current, the research is ongoing, new information is constantly emerging and advances continue to be made. The scientific controversy that has surrounded evolutionary explanations of human behaviour is a sign of the vigour and potential strengths of the field.
