As a nerd not quite popular in girls, I haven’t got any real experience to support this topic. Having sex for fun without taking the corresponding responsibility is beyond one’s wildest dream. Well, you may snort at this cynicism(zuo4 meng4). Although only fancy guys can have sex with dozens of girls, just like the situation in many species, the truth is that most of us will have long-term sexual partner and intercourse itself is still a private behavior. That’s something non-trivial from the view of zoology. Instead of taking it for granted as the result of human civilization, Diamond tries to explain it from sexual strategies in selection, which is decided by both ecological parameters and parameters of a species’ biology. He points out that, on the contrary, sexuality, as well as large brains and upright posture, participates in building the distinctive human features.
Disappointing as it may be, the sensational headline only makes a small part of the book. What the author is interested in is the bizarre traits that distinguishing us from other animals: “sexuality-long-term sexual partnerships, co-parenting, proximity to the sexual partnerships of others, private sex, concealed ovulation, extended female receptivity, sex for fun, and female menopause-constitute”.
For those who have taken the Human Physiology and Sexual Health, one of the famous courses in PKU (I should recommend it here), you may not be stunned by the comparisons: reading Chap.I & II through only broadens your lexicon in this field. But in the following chapters, Diamond gives you stories can’t be seen in physiology or evolutionary biology class. I will brief two of them here: The first is “Why males and females shares almost balanced nursing responsibility?” and the second “Why the ovulation can’t be observed easily in human?”
Feminists will argue that the first one is merely a pseudo-problem: How could men share the pain in delivery? And how can we say they are co-parenting if they cannot feed the baby with their breasts? Well, if we step back from anthropocentrism to zoo-centrism, man may be the most selfless male animal. Perhaps we should not measure other species in terms of our own value, for natural selection may be the dominating factor in rearing behaviors, including us.
For both sexes, only sexual strategies which maximize the survival of genes can be seen today. Besides the cooperation of bearing offspring, there is also a battle between the two sexes in getting off the rearing burden. Protecting and feeding the young rather than philandering may be a stupid “choice” if: a) The child can be easily survived without or with little care from parents; b) There is possibility that the baby is not genetic correlated with me; c) There is plenty chances to copulating with other mates and give more children outside. Most other female animal can give birth and raise its children without others’ help, which can hardly be seen in human society: even today’s single mothers suffer a lot, let alone those of the hunter-gather society. For humans, most food is acquired by complex technologies far beyond the dexterity or mental ability of a toddler. As a result, our children can live by themselves at least a decade after weaning. In this case, both parents’ care is indispensable.
Generally speaking, female animals are restricted physiologically to intercourse more or less when they are pregnant. And mothers are pretty sure the children they are raising are genetically their offspring. But the same isn’t sure for the male. That’s why male animals desert their mates and children easily soon after copulating.
Fortunately, the possibility of taking care of your rivals’ children (xi3 dang1 die1) is not that high in human society. Though we see cuckolds at times in movies and shows, genetic tests have shown that more than 95% of the babies in the U.S. are legitimate, that is, by the mother's husband. Taking care of your spouse life-time and keep a long-run sexual relationship with her seems worthwhile.
The second question is even trickier, for there are plethora hypotheses to explain concealed ovulation. Among them, “daddy-at-home” theory and “many-fathers” theory seem to be most plausible, though they virtually opposite with each other. “daddy-at-home” views concealed ovulation as a strategy to avoid being desolating by his husband. Because once husband knows that his wife is not ovulating that day, he will turn to outside options safely. Thus concealed ovulation will clarify paternity and reinforce monogamy. Notice we are not talking about today’s human society yet, our ancestor “care” more about the result of fertility rather than their fame. The alternative theory, the “many-fathers” theory comes up from the of infanticide phenomenon. A clear ovulation does clarify the paternity of babies, but it may incur infanticide when a new father come, which impairs to the mother’s genetic benefit. A clever strategy is concealing ovulation and hoping the new-comer would give up infanticide in case killing his own children. If this theory is true, concealed ovulation confuses paternity and effectively undoes monogamy. No matter through which theory, selection eventually renders women unconscious of her ovulation as well so by no means can a male detect it.
It’s impossible to evaluate these two competing theories within the limit history of human beings. Swedish biologists Birgitta Sillen-Tullberg and Anders Moller came up with a method by looking into the family tree of living primate species. By imputation of unrecorded ancestors using Evolutionary Commitment reasoning, the final result is: a)Promiscuity or harems, not monogamy, is the mating system that leads to concealed ovulation; b)Monogamy has usually arisen in species that already had concealed ovulation, and sometimes in species that already had slight ovulatory signals.
So why is sex fun? So far we see more battles than cooperation between male and female. If we follow Diamond’s logic, the only possible explanation is it severs the male’s, the female’s or perhaps both sexes’ genetic interest. It would be a miserable fact if genetic interest is the very basis of most of, if not all of, the behaviors between couples. This somewhat goes too far from what we can bear: For chivalrous gentleman (diao3 si), taking care of a lovely girl is joyful itself. Nevertheless, the paradox of sexual selection is a process when there is a battle between different sexes, there are also one thousand battles within the same sexes. Thus, no gender has absolute power to the other. Through the rude and tyrannic competition and selection, we are lucky to witness the unprecedented sexual harmony, at least from human-beings’ point of view today.
Up to now, you may find out that this book is full of stories in the very long run, perhaps billion times as our life. For those who read it for tips to have more fun in sex or hook up with girls, they may be disappointed. But still, reading it should not be a waste of time, since human may be the only creature on earth who has the power to challenge natural selection. Diamond believes lactation by men is totally possible in the future, physiologically and psychologically: It’s the direction of evolution. It hasn’t happened simply because our evolution speed is too slow. Similarly, finding out the selection logic of sexual strategy may render you an edge both in competing with your same-gender peers and understanding your spouse’s philosophy. Have fun.