Mankind is an ape. Of the five species of ape, three are social, and in two of those, chimpanzees and gorillas, it is the females that leave the home troop. In the chimpanzees of Gombe Stream in Tan-GENETIC MUTINY AND GENDER
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zania studied by Jane Goodall, young males born to senior females tend to rise to the top faster than males born to junior females.
Therefore, female apes of high social status 'should '—according to the Trivers-Willard logic—have male young and those of low social status 'should ' have female young.' Now men are not excessively polygamous, so the rewards of large size to men is not great: big men do not necessarily win more wives, and big boys do not necessarily become big men. But humans are a highly social species whose society is nearly always stratified in some way. One of the prime, indeed, ubiquitous perquisites of high social status in human males, as in male chimpanzees, is high reproductive success.
Wherever you look, from tribal aborigines to Victorian English-men, high-status males have had—and mostly still do have—more children than low-status ones. And the social status of males is very much inherited, or rather passed on from parent to child, whereas females generally leave home when they marry. I am not implying that the tendency for the female to travel to the male 's home when she marries is instinctive, natural, inevitable, or even desirable, but I am noting that it has been general. Cultures in which the opposite happens are rare. So human society, like ape society but unlike most monkey society, is a female-exogamous patriarchy, and sons inherit their father 's (or mother 's) status more than daughters inherit their parents ' status. Therefore, says Trivers-Willard, it would pay dominant fathers and high-ranking mothers, or both, to have sons and subordinates to have daughters: Do they?
The short answer is that nobody knows. American presidents, European aristocrats, various royals, and a few other elites have been suspected of having male-biased progeny at birth. In racist societies, subject races seem to be slightly more likely to have daughters than sons. But the subject is too fraught with potential complicating factors for any such statistics to be reliable. For example, merely by ceasing to breed once they have a boy—which those interested in dynastic succession might do—people would have male-biased sex ratios at birth. However, there certainly are no studies showing reliably unbiased sex ratios. And there is one tantalizing study from New Zealand that hints at what might be found
if anthropologists and sociologists cared to look into the matter.
As early as 1966, Valerie Grant, a psychiatrist at the University of Auckland in New Zealand, noticed an apparent tendency for women who subsequently gave birth to boys to be more emotionally independent and dominating than those who gave birth to girls: She tested the personalities of eighty-five women in the first trimester of pregnancy using a standard test designed to distinguish 'dominant ' from 'subordinate ' personalities —whatever that may mean.
Those who later gave birth to daughters averaged 1:3 5 on the dominance scale (from 0 to 6): Those who later gave birth to sons averaged 2.26, a highly significant difference. The interesting thing about Grant' s work is that she began before the Trivers-Willard theory was published, in the 1960s. 'I arrived at the idea quite independently of any study in any of the areas in which such a notion might reasonably arise, ' she told me, 'For me the idea arose out of an unwillingness to burden women with the responsibility for the 'wrong ' sex child.'
SELLING GENDER
Almost no subject is more steeped in myth and lore than the business of choosing the gender of children. Aristotle and the Talmud both recommended placing the bed on a north-south axis for those wanting boys. Anaxagoras 's belief that lying on the right side during sex would produce a boy was so influential that centuries later some French aristocrats had their left testicles amputated. At least posterity had its revenge on Anaxagoras, a Greek philosopher and client of Pericles: He was killed by a stone dropped by a crow, no doubt a retrospective reincarnation of some future French marquis who cut off his left testicle and had six girls in a row.'
GENETIC MUTINY AND GENDER
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It is a subject that has always drawn charlatans like blow-flies to a carcass: The old wives ' tales that have answered the pleas of fathers for centuries are mostly ineffective: The Japanese Sex Selection Society promotes the use of calcium to increase the chances of having a son—with little effect: A book published in 1991 by two French gynecologists claimed precisely the opposite: that a diet rich in potassium and sodium but poor in calcium and magnesium gives a woman an 80 percent chance of conceiving a son if consumed for six weeks before fertilization: A company offering Americans 'gender kits ' for $50 was driven into bankruptcy after the regulators claimed it was deceiving the consumer:'
The more modern and scientific methods are somewhat more reliable. They all rely on trying to separate in the laboratory Y-bearing (male) sperm from X-bearing (female) sperm based on the fact that the latter possess 3.5 percent more DNA. The widely licensed technique invented by an American scientist, Ronald Ericsson, claims a 70 percent success rate from forcing the sperm to swim through albumen, which supposedly slows down the heavier X-bearing sperm more than it does the Y-bearing sperm, thus separating them. By contrast, Larry Johnson of the United States Department of Agriculture has developed a technique that works efficiently (about 70 percent male offspring and 90 percent female:) It dyes the sperm DNA with a fluorescent dye and then allows the sperm to swim in Indian file past a detector: According to the brightness of the sperm 's fluorescence, the detector sorts them into two channels: The Y-bearing sperm, having smaller amounts of DNA, are slightly less brightly fluorescent: The detectors can sort sperm at >oo,000 a second: Early concerns that the dyes might cause genetic damage have been largely allayed by animal experiments and this technique is now being used in the United States, mostly by people who wish to ' balance the family'—have a girl after a string of boys, or vice versa:
Curiously, if humans were birds, it would be much easier to alter the chances of having young of one gender or the other because in birds the mother determines the gender of the embryo, not the father: Female birds have X and Y chromosomes (or some-
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times just one X), while male birds have two Xs. So a female bird can simply release an egg of the desired gender and let any sperm fertilize it. Birds do make use of this facility. Bald eagles and some other hawks often give birth to females first and males second.
This enables the female to get a head start on the male in the nest, which enables it to grow larger (and female hawks are always larger than males). Red-cockaded woodpeckers raise twice as many sons as daughters
