Geneticists have long argued about the effects of having an extra male chromosome, a condition found in 1 of 1,000 men

A battered paperback entitled The XYY Man, by Kenneth Royce, leans in a corner of my bookshelf. It’s a spy novel that chronicles the adventures of “Spider” Scott, an ex-felon who wants to become law-abiding, but finds that he is genetically predisposed to criminality because he has an extra chromosome. Unlike most men whose XY sex karyotype imparts their maleness, Scott has been endowed with an XYY karyotype by his novelist creator.

This condition is not fanciful. XYY syndrome first appeared in the medical literature in 1962, eight years before Royce published his book. A team of researchers from Roswell Park Medical Institute in Buffalo, N.Y., described the first XYY person on record, a 44-year-old man who had undergone genetic testing because one of his children had Down syndrome. Though never before reported, this extra-chromosome condition produced during early cell division has turned out to be not tremendously rare, affecting about 1 in 1,000 boys. In most men who have it, the 47th chromosome causes no problems whatsoever, and more than 95 percent of XYY guys don’t realize they are specially endowed.

For decades, however, geneticists argued over the reputed social hazards of XYY syndrome. Did the extra chromosome make its bearers “supermales,” men who behaved as if they were amped up on too much testosterone? Some believed that XYY men, like “Spider” Scott, were inherently violent and prone to committing criminal acts. The dispute captured the public’s imagination, spawning several sequels to Royce’s novel along with numerous movies and TV shows (such as Law and Order) featuring dangerous and socially conflicted XYY characters.

During the late 1960s, geneticists, sociologists, and others began looking at prison populations to see if XYY men were disproportionately represented. Many people asserted that not only did XYY men commonly have violent criminal tendencies — the biochemist Mary Telfer characterized them as “perhaps too highly sexually motivated” — but that such males could be diagnosed by physical and mental traits, which included tall stature, long limbs, facial acne, mild mental retardation, and aggressive behavior.

In 1970 geneticist H. Bentley Glass advocated the relaxation of abortion laws to allow women to end pregnancies if the fetus was XYY. Speculation even ran that Richard Speck, the infamous murderer of eight student nurses in Chicago in 1966, owed his propensity to violence to an extra Y chromosome. That proved untrue. In one notorious case of the mid-1970s, a British court wrongfully convicted Stefan Kiszko of the murder of an 11-year-old girl largely because of his XYY karyotype, and it took more than 15 years for him to win release from prison.

In recent years, geneticists have learned more about the actual effects of the XYY condition. XYY boys may be delayed in maturation, are taller on average and more physically active, and sometimes display learning and behavioral problems. Their intelligence, testosterone levels, aggressiveness, sexual development, and fertility typically fall within the normal range. They grow into men who are unrecognizable to the general public.

In the mid-1970s, a Danish study showed that XYY men were not more likely to commit violent crimes, although they did have more convictions for other crimes. A long-running follow-up study published this year confirmed those findings and attributed the higher conviction rate for such crimes as sexual abuse, arson, and burglary to “unfavorable living conditions” — poverty, joblessness, and other disadvantages resulting from a lack of childhood support that many XYY men experience.

Slowly, as the suppositions of the 1960s have given way to current research, the public is changing its thinking on XYY syndrome. Few people today believe that an extra Y chromosome condemns its owner to a life of violent crime. Genetic counselors explain the condition to families and teach ways to nurture XYY boys. Men like the fictional “Spider” Scott can exercise their free will without fear that a sex chromosome has turned them bad.

Leave a Comment