7.3 Family structure
Evolutionary theory suggests that the differential strategies of men and women influence family structure. Biological differences, for example in the size of men and women, can provide clues about the structure of pairing bonds. Human males are around 1.15 times bigger than females, suggesting that males have competed for females in evolutionary history. Biologists also suggest that there is a correlation between the size of testes and the level of promiscuity of a species—the larger the testes, the more promiscuous the species is likely to be. Human males have relatively small testes relative to body size (bigger than monogamous gibbons, but smaller than promiscuous chimpanzees), indicating that in the evolutionary past females were not promiscuous, but not wholly monogamous either (Ridley 1993).
While polygyny is the most common evolutionary strategy for mammals, humans are exceptional among mammals and are more like most birds in typically, but not always, adopting monogamy. This is related to the enormous effort that is required in rearing a human infant. Human children are very dependent for a long time and need the full time care and attention of both parents. The evolution of prolonged helplessness in human infants that required more resources and attention than the mother alone could provide is likely to be the origin of the two-parent family and the caring role of the father (Chisholm 1999).
The prolonged dependency of human children requires parental care for a long time, and parents who cared for their children are likely to have had mhrdore descendants than those who did not. Natural selection, therefore, is likely to have endowed parents with emotions such as love, solicitude and commitment to invest resources and attention in their children (MacDonald 1992). Men invest in their offspring, providing more than genes—they love, feed, protect and teach their children. This pattern is likely to have evolved in egalitarian hunter-gatherer societies, and when males are relatively equal in status, monogamy is the norm.
However, when some males can monopolise sufficient resources to allow a female to survive and reproduce, they can use this control to attract mates and compete with other males for dominance. Polygyny and an increase in the variance of male mating success will result (Winterhalder and Smith 2000). Unlike the monogamy likely to have been the norm in hunter-gather societies, the development of agriculture allowed men, predisposed to compete for status, to accumulate wealth, power and wives—resulting in polygyny (Hrdy 1999). Male coercion arising from wealth power and can severely constrain female choice, since most women seek monogamous marriage, even in societies that permit polygamy. They want to choose a man carefully, get his help in rearing children and monopolise him for life (Ridley 1993). In polygynous societies, it is only the wealthiest and powerful men who can afford more than one wife at a time, so most marriages are monogamous, but there are more (low status) bachelors than spinsters.
Most human societies practice effective polygyny—women are a contested resource and successful men routinely convert their status and power into monopolising their access to multiple women. Even in monogamous societies, infidelity, divorce and remarriage biased towards wealthier and higher-status males create a situation of effective polygyny. At the same time, many men may not be able to attract and support several women, so monogamy may be the norm for most people. Men with low status and few resources face strong competition and may not be able to attract female favour. Men at this end of the scale may face complete reproductive failure.
The “young male syndrome” (involving behaviours such as risk-taking, stealing, violence, egotism and sexual misdemeanours) can be seen as an adaptive response to uncertain and risky environments to maximise reproductive success. Early stress and poor attachment as an infant can lead to subjective experiences of insecurity that contribute to the “young male syndrome” (Chisholm 1999). The evolutionarily rational risk-taking behaviour of disadvantaged young men with poor education and few prospects is mirrored in contemporary society by their disproportionate involvement in illegal activities such as drug-taking and crime.
It can also be evolutionarily rational for young women in uncertain and risky environments to take risks. Early childbearing and/or a high rate of reproduction may thus be an adaptive response. Sole motherhood may also be a rational response to risk and uncertainty in women’s lives where men do not have reasonable and predictable access to the resources that women require to bear and raise their children (Geronimus 1997). In these circumstances it may be an adaptive response to maximise current reproduction to choose a man for genetic rather than parenting fitness—selecting on the basis of his current contribution (genes) rather than future investment (parenting resources). The payoff to seeking a man who will be a good and secure provider in the future in these circumstances may be low and take time (Chisholm 1999).
This “young female strategy” is a counterpoint to the “young male strategy” in chronically risky and uncertain environments. Like the “young male strategy” the “young female strategy” undermines long-term monogamy. In environments with many poor, low status men with little ability to support a family, women may become accustomed to sex without commitment and to bringing up children on their own (Wright 1994a). The focus on current reproduction rather than long-term parenting means that emotional attachment may be short-lived and non-exclusive. Maintaining a monogamous relationship with a low-status man with few resources to offer may also disadvantage a woman. Not only may he fail to provide for the woman and her children, but he may also compete with the children for available resources and preclude her choosing another “better” man. Furthermore, she may be subjected to violence as the result of sexual jealously that is part of the “young male syndrome”.
By maintaining relationships with a number of men, especially men who are the fathers of her children, a woman can spread the risk of unpredictable resources among many men (see for example Shotak 1981). By not allowing any one man to live long with her and her children, she can limit sexual jealously. She can also maintain links with the relatives of each man—adding to the potential sources of resources for her children. Sole motherhood often occurs in the context of several generations of women in an extended family, allowing access to the wider family’s resources. This “facultative polyandry” can be an adaptive reproductive strategy under conditions of risk and uncertainty that can improve the resources available for the children and increase their chances of survival to adulthood (Hrdy 2000). The “young female strategy” is reflected in contemporary society by a large number of single mothers with poor education and few job prospects.
