PAIR BONDING MONOGAMY

EV 2001: When females choose a trait that is an honest indicator of good genes, that trait spreads throughout the population over generations…A deep biological dilemma: for some species, the chances of their offspring surviving increase if a female chooses a mate who will stick around, over the one with the best genes. Evolution has favored, in many species, males and females who share the job of parenting.

RP 1999: In species like birds, where infants need constant care, the bonding together of parent couples is common. Pair bonding among humans also likely results from infant dependency because children require adult supervision for many years. But such monogamy is rare among mammals: just three percent of mammals mate with a single spouse for a lifetime. Human beings are an exception, to a degree…Man was not even remotely aware of his own physical role in the production of children. That knowledge seems not to have come until the early days of farming, sometime after 10,000 B.C.E., and…it crystallized his sense of possessiveness, for the concept of "my son" required the child's mother to be tied to one man only.

EV 2001: Male songbirds are only going to give up philandering if he believes the chicks he's staying home to help raise are his own. The result is monogamy, a social solution to a biological dilemma. Human infants are also born heavily dependent on parental care…but monogamy isn't easy to attain, while some evolutionary forces encourage it, others threaten the family values that are at its core.

RP 1999: By studying various primates, anthropologists find clues to human evolution. For example, whereas the promiscuous female chimpanzee will mate with a series of males and bond with none of them, a female gibbon monkey bonds exclusively with one mate for many years. This may be because, like a human female, the gibbon lacks an estrus cycle, the reproductive cycle that drives most other female primates (like the chimpanzee) to seek intercourse during peak days of ovulation. Estrus cycles inspire promiscuity, because most female primates avoid sex when they are not ovulating, so male primates are in constant pursuit of any mate who is at the receptive stage of her cycle and ready for sex.

EV 2001: It turns out that when women are ovulating, and the chances of getting pregnant are high, there is a consistent shift in what they find attractive toward a more masculine looking male. Just like with the songbirds, that's when the unconscious lure of those "good genes" is strongest.

RP 1999: But since the female gibbon, like a human female, lacks an estrus cycle - and is therefore receptive during more days of her monthly menstrual cycle - a male can form a lasting bond because sex is accessible to him more often with this single mate. This is the theory behind monogamous mating, but it doesn't explain why a human female, even when receptive for sex throughout her menstrual cycle, often chooses to court several partners anyway, rather than bond with just one male. In fact, during the five thousand years of recorded history, most people have mated in a promiscuous way. "If, in the early days, humanity bore a strong family resemblance to the chimpanzee," explains Tannahill, "at least one major biological change must subsequently have taken place . . . the human female's menstrual cycle must gradually have replaced the estrus cycle of the primates, a modification with long-term results in the case of the female's own sexuality, and long-term repercussions on the relationship between men and women."

RP 1999: Both monogamy and polygamy have flourished among humans at differing times throughout pre-history. Such mating behaviors are adapted to the changing environment. With our needs shaped by a variety of unstable forces, flexibility in our response increases our chance for survival. "Perhaps the most reasonable hypothesis is that the human race originally resembled its chimpanzee relatives in being promiscuous," concludes Tannahill.