Why, Oh Y…, Carl Zimmer

Discover, June 30, 2003

In the 1960s, a team of scientists studying the DNA of men imprisoned in a Scottish institution for violent offenders reported that a disproportionate number of them carried an extra Y chromosome. From that correlation the scientists theorized that this abnormality more or less doomed a man to a life of violent crime. One Y chromosome programs a fertilized egg to become male; the Scottish researchers concluded that if you double the Y–as happens in one out of every thousand male births–then you double all the aggression ostensibly hardwired into all men.

Yet, as Steve Jones points out in his book Y: The Descent of Men, the underlying science was faulty. The original study that kicked off the XYY craze was based on a grand total of two men whose cells harbored the extra chromosome. When scientists later looked at bigger samples, the correlation weakened. Some scientists still insisted that an extra Y might produce a slight tendency toward antisocial behavior. But even that fragile link has been attacked, and now geneticists generally dismiss it altogether.

The extra-chromosome canard is one of many myths about manhood that Jones sets out to demolish in his witty, informative book. Jones, a genetics professor at University College London, offers his readers a tour through the latest research on the male sex, drawing on work ranging from endocrinology to ornithology. The perspective that emerges is fascinating in its complexity. The path that a fertilized egg takes once it gets a Y chromosome, for example, is not a straight shot to machismo. At every step of the way, hormones and environmental forces put it in “constant danger of being forced back onto the broad path to femininity,” Jones writes.

Jones knows full well that many of his fellow scientists want to cook manhood down to simple slogans. Evolutionary psychologists, for example, claim that the minds of men are shaped by the ancestral urge to spread their seed. But Jones argues that the definition of a man shifts with the culture in which he lives. Today’s man shares the workplace with women, he may have children through in vitro fertilization, and he may use Viagra to help promote matrimonial bliss. To ignore this cultural reality, to try to stamp all men with some genetic or evolutionary brand, is foolish. After all, the males of our closest animal relatives, chimpanzees and bonobos, lead utterly different lives. Male chimpanzees rule despotically over females, while male bonobos live at the edge of a female-centered orgy. “Animals have males, but only Homo sapiens has manhood,” Jones says.

Although Y is only 272 pages long, Jones packs it with detail. Readers learn about the latest technology for castrating cattle, the medical consequences of circumcision, the secrets revealed by paternity testing, and the sperm-filtering anatomy of female crickets. Yet although many of his anecdotes are entertaining–such as the one in which scientists boiled 6,000 gallons of urine in search of testosterone–they don’t come together into a compelling narrative. Perhaps Jones decided that a mountain of details would confound readers with the complexity of manhood. But Y ends up more scrapbook than book. Scrapbooks do have their joys, though. Just watch what happens at the next party when you casually bring up the hydraulics of erections or the fruit flies that make finger-length sperm. Once you have everyone’s attention, be sure to set them straight on the double Y.