Is there a gene for mass murder? Of course not. But within a week of the December 14 elementary school massacre in Newtown, state authorities were planning to do genetic tests on the tissues of the man who committed the horrific crime and then killed himself. There are real risks involved in this, and few — if any — scientific merits.

Even the first reports of the decision to examine Adam Lanza's DNA included warnings from experts. Last week, Nature weighed in with an editorial that stated bluntly:

Lanza's DNA will be analysed not because it will be useful but because it can be analysed. The ease of DNA sequencing will lead to a dangerous temptation to focus on minor, even spurious, genetic correlations at the expense of non-genetic factors that are more influential.

But aside from being a distraction, can sequencing Lanza's genes do any harm? Why not give them a look?

As a society, we have a record of attributing criminal tendencies to biological traits, and basing social policy on the results. Remember phrenology? Remember eugenics? Another false scientific theory that is particularly relevant is the "criminal chromosome." The 1961 discovery that some men have two Y chromosomes led to the suggestion that they must be doubly male — "super male" — and therefore prone to aggression. In 1968 The New York Times and other major publications jumped on this bandwagon. Social consequences soon followed:

  • Newborn screening programs were set up in several states to identify baby boys who were XYY.
  • In 1970, President Richard Nixon's personal medical advisor proposed testing the genes of every American child between ages six and eight, in order to identify those with "criminal potential." He suggested that "hard-core 6-year-old" children be sent to "camps" where they could learn to be "good social animals."
  • In the same year, the eminent geneticist H. Bentley Glass told the annual meeting of the American Association for the Advancement of Science that he looked forward to the time when pregnant women would be required by the government to abort XYY "sex deviants."
  • Defense lawyers began to use their clients' XYY status in criminal trials, in France, Germany and Australia as well as in the U.S.
  • A psychologist at Johns Hopkins Hospital tried to treat 13 XYY boys and men with behavior problems by chemical castration. It didn't work, but its side effects included weight gain — and suicide.

Most of this happened after there was expert testimony and published research

showing — correctly — that XYY men were not more likely to be criminal than XY men.

In the wake of a tragedy like the Newtown massacre, it may be understandable to grasp at simple explanations, and to fall prey to spurious correlations. But to think that genes will tell us who to fear is a serious misunderstanding of genetic science. And history tells us that such erroneous ideas are extremely likely to lead to demonizing some group of people, whether identified by the shape of their head or the color of their skin or the religion of their ancestors — or the particular configuration of their DNA.

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