On Men Women and Evolution- Testing the Myth
Session 1
Love and sexuality are far and away the most important emotional phenomena for our direct genetic survival. It is no surprise that nearly 80 percent of people surveyed by Daniel Kahneman and his colleagues in the course of their research on happiness reported that sexuality and love are the most decisive factors in their lives for achieving happiness.1 The other rational emotions are important for evolutionary survival because they increase our fitness to our environment and our personal chances for survival. But love and sexuality directly contribute to our genetic survival by enabling us to reproduce and raise offspring.
Love is not a mechanism that is needed for reproduction in most animals, for whom sexual relations alone suffice. These typically involve brief sexual encounters, often only once with each mate, with males taking on little or no responsibility for caring for their offspring.
Many of us may also know humans who fit this description in their attitudes toward sexual relations. But most of humanity exhibits a different pattern of sexual behavior. The institution of marriage, a nearly universal cultural phenomenon, is a strong expression of the more typical human attitude toward love and sexuality. This distinction between human sexuality and that of most animals is related to the fact that raising a human child is a very long and complex process requiring the involvement of more than one parent.
While humans wait patiently for up to a full year or more for infants to learn to walk after their births, newborn gazelles are up and walking within two days of their births. Equine mares watch their newborn foals take their first steps within half a day of birth.
The life expectancy of gazelles and horses is shorter than that of human beings, but it still ranges up to about thirty years. Raising a human child to the point of complete independence from adult care and supervision takes about 20 percent of modern human life expectancy. Until about two hundred years ago, it required as much as 30 percent of life expectancy. There are virtually no other animals that go through such a lengthy juvenile period relative to their life expectancies.
From the evolutionary perspective there is no point in having offspring unless those offspring in turn have offspring of their own. Only a child who has reached independent adulthood can contribute to the genetic survival of his or her parents. If childhood were sufficiently short relative to the life span of a single parent, and demanded relatively few resources, mothers could reasonably care for their offspring on their own. The longer childhood lasts and the more one needs to invest resources in raising a child, the more important it becomes for the father, who also benefits (genetically) from having offspring who successfully reach adulthood, to share in the burden of raising the child.
In my book "Feeling Smart: Why our Emotions are More Rational than We Think" I look into the roles that social emotions play in creating commitment. Anger, for example, helps us create credible threats. Love, in contrast, creates credible commitment for altruistic behavior toward mates, a commitment that is a precondition for parental cooperation in caring for offspring. From the male perspective, the commitment arising from love within a couple increases the chances that the child he is helping to raise is indeed his child, carrying genes that are similar to his, and not the child of another man with whom his spouse has had relations. Love and social structures that are built on stable monogamous relationships are the result of the large amount of parental energy humans need to invest for the successful survival of their offspring.
Human parents generally care simultaneously for children who were born in different pregnancies. This is not a phenomenon that characterizes other animals, whose offspring leave their parental nests before their mothers reproduce again. My colleague Motty Perry coauthored an excellent paper that used game theory to show that this phenomenon is responsible for the familiar structure of the human family, in addition to the commitments that members of couples exhibit toward each other.2 Without these commitments, men would never know if the food that they have worked so hard to obtain and give to their spouses will be passed on to feed their children as opposed to the children of other men from previous pregnancies.
Human childhood is very lengthy because human children need to learn complex social skills, over and above the physical and cognitive growth that all animals undergo as juveniles. Very few animals form long-term stable couplings with a single mate (hamsters and foxes are two noteworthy exceptions). The vast majority of animals have what we humans might call far more "steamy sex lives," based on casual sexual encounters. The sole purpose of their sexual interactions is procreation. Sexuality in these species is based on intense and sometimes violent "sperm competition" between males, along with selective female receptivity to the mating efforts of the males, with only the males deemed most fit on the part of the females succeeding in mating.
(Next week: Strategies in "Sperm Competition")
Session 2
Last week we mentioned:
1. This distinction between human sexuality and that of most animals is related to the fact that raising a human child is a very long and complex process requiring the involvement of more than one parent.
2. Sexuality most species is based on intense and sometimes violent "sperm competition" between males, along with selective female receptivity to the mating efforts of the males, with only the males deemed most fit on the part of the females succeeding in mating.
We now continue:
The specific characteristics of sperm competition between males vary from one species to another, depending on evolutionary developments. Competition between drones (male bees), for example, comes down to a total of about ten minutes out of their very brief lives. When a virgin queen bee is ready to mate, she enters a vigorous dancing state, drawing a swarm of drones. Only the strongest and quickest drones can succeed in mounting the larger queen bee and inserting their sperm into her. The drones die shortly afterward, while the queen bee stores their sperm for the rest of her life (up to thirty years) for use in fertilizing the millions of ova she produces.
Sperm competition between male mice is no less interesting. Its main expression comes after the act of mating has been completed. After inserting his sperm into a receptive female, the male secretes a sticky substance that essentially blocks the female's reproductive tract to prevent other males from successfully mating with her until his sperm has been fully absorbed inside the female. This strategy, reminiscent of the chastity belts that the knights of the Middle Ages once locked their wives in before going out to battle, increases the male's chances of successfully fertilizing a female with whom he mates and also incentivizes him to care for her offspring because he has greater certainty that her offspring are his.
Sperm competition strategies vary widely between species, but generally it is one of two kinds of evolutionary strategies for ensuring the survival of one's DNA. The other is a "marketing strategy" (think of the peacock's tail and other characteristics and behaviors that can be explained using the handicap principle) used to increase the attractiveness of individual males in the eyes of females.
Men and women have evolved differences in their emotional and sexual behavior due to physiological differences related to reproduction between the two sexes. Reproductive asymmetries between men and women are expressed in three main ways:
1. The maximal number of children that a woman can bear in a lifetime is well below one hundred (the best documented historical record of the greatest number of children borne by one woman is held by a Russian peasant woman who lived in the eighteenth century and gave birth to sixty-four children through twenty-seven pregnancies). In contrast, a man can theoretically father 100,000 children. Similarly, while a woman can reach her maximal reproductive potential by mating with only one man throughout her life, a man would need about a thousand women to attain his maximal reproductive potential.
2. A woman knows with exact certainty who her biological children are: the children emerging from her womb. A man can never be certain whether the children borne by his spouse are indeed his biological children.
3. In the reproductive process itself mothers invest far more resources than fathers because mothers carry fetuses within them for nine months of pregnancy.
In addition to these three differences, men and women differ in one more relevant physiological actor: men on average have greater muscle mass than women.
To get an idea of the extent to which these physical and physiological distinctions influence differences in emotional reactions and sexual behaviors between men and women, I will review several widespread clichés, taking a close look at each one. Keep in mind that the evolutionary forces that have been shaping differences between the sexes long predate the feminist revolution and the modern era. They existed before human civilization arose, under conditions of a daily struggle for survival in which lack of close care for a child on the part of both parents meant almost certain death for the child.
To be continued next week same time with testing of varoius cliche's on gender differences. Stay tuned!
Session 3
Last week we discussed the reproductive asymmetries between men and women. We mentioned that they are expressed in three main ways:
1. The maximal number of children that a woman can bear in a lifetime is well below one hundred, while, a man can theoretically father 100,000 children.
2. A woman knows with exact certainty who her biological children are: the children emerging from her womb. A man can never be certain whether the children borne by his spouse are indeed his biological children.
3. In the reproductive process itself mothers invest far more resources than fathers because mothers carry fetuses within them for nine months of pregnancy.
Cliché 1: Men are far more likely than women to agree to brief one-time sexual encounters without emotional commitments.
The facts: A man can theoretically father a thousand times as many children as any one woman can bear. In practice, men and women have the same number of children on average for the simple reason that each child has precisely two biological parents. This brings about a situation in which men are in perpetual competition with other men in the race for greater fertility. From this perspective, a long-term commitment to one partner reduces a man's genetic survival potential because it limits the number of children he can have to the upper limit of children that his partner can bear for him. In contrast, women need only one man to attain their maximal fertility, and gain no advantage in having multiple sexual partners.
The facts: As noted above, having sexual relations with multiple partners without any emotional commitment has no effect on the number of children a woman can bear. On the other hand, it does reduce her children's chances of survival, because if she has no partner with an emotional commitment to her and her children, then none of the fathers of her children is likely contribute to the burden of raising the children. If she is alone in the task of providing for her children, they are likely to have less protection and less food than they would if they had a father helping to raise them. Procreation in general is more resource-demanding for women than men because a woman can have only one child every nine months, during which she needs to invest a great amount of energy in pregnancy and childbirth. As a result, women need to be much choosier than men in mating, and they need to ascertain that their mates will be committed to them and to their children.
Cliché 3: Women are more anxious than men when it comes to their health and the well-being of their children, while men become more nervous than women when their health shows signs of failing.
The facts: The image and stereotype of the "caring and worrying" mother is common in many cultures, and for good reason. Because women are more limited than men in the number of children they can have, they need to invest more resources than men in protecting the children that they already have. This is the evolutionary source of the "caring and worrying mother" figure. When all her children have achieved adulthood and her years of fertility are behind her, usually when she is in her fifties, a woman's task in directly ensuring her genetic survival is over. But a man at that age can still contribute to his genetic survival by fathering more children. Only death or disease can limit his further fertility. In other words, from the perspective of genetic survival, from age fifty and above only men have "something to lose," which may be the source of male hypochondria in their later years.
To be continues next week with more Clichés
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