The Red Queen_ Sex and the Evolution of Human Nature - Matt Ridley [60]
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’ 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.61
It is a subject that has always drawn charlatans like blowflies 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 gynaecologists claimed precisely the opposite: that a diet rich in potassium and sodium but poor in calcium and magnesium gives a woman an eighty per cent 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.62
The more modern and scientific methods are only slightly 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 three and a half per cent more DNA. The widely licensed technique invented by an American scientist, Roland Ericsson, which opened its first British clinic in 1993, claims a high success rate, but has not published convincing data. It relies on causing 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 indeed developed a technique that works efficiently (about eighty per cent male offspring), but it is wholly unsuitable for human beings. 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 the sperm at a hundred thousand a second and the sperm can then be used to fertilize embryos using in vitro fertilization. But no human being in his right mind would submit his sperm to such dyes or go through expensive in vitro fertilization just to have a boy.63
Curiously, if humans were birds, it would be much easier to alter the chances of having young of one gender or another, because in birds it is the mother that determines the gender of the embryo, not the father. Female birds have X and Y chromosomes (or sometimes 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 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 and use spare sons as nannies for subsequent broods. Among zebra finches, as Nancy Burley of the University of California at Santa Cruz discovered, ‘attractive’ males mated with ‘unattractive’ females usually have more sons than daughters, and vice versa. Attractiveness in this species can be altered by the simple expedient of putting red (attractive) or