It sounded scientific enough: the shape of your skull, it was once widely believed, reflected your personality. That was thought to correspond with the shape of the brain, and indicated which parts were bigger or smaller than average. This idea, known as phrenology, originated with Franz Joseph Gall, a German doctor, and became popular in the early 19th century.
We now know it was all nonsense, of course. Gall had the idea after measuring the heads of pickpockets. But his theory was based on a handful of examples and a shedload of prejudices. Phrenology was used to justify slavery, supposedly showing that Europeans were mentally superior to other races, and that women were better suited to child-rearing than intellectual pursuits.
We’d do well to remember this as we consider the current craze for individual DNA testing. Like phrenology, many such tests promise to reveal your true identity: your ethnic origin, susceptibility to disease, academic aptitude or tolerance for particular foods. These results ought to be treated with scepticism, however. If a DNA test says you are 30% Italian or 5% Scandinavian, it doesn’t mean that your ancestors were Romans or Vikings – just that you share genes with people who live in those parts of the world now. DNA testing can be useful for people who want to identify lost cousins, but ethnicity figures are based on quite a bit of guesswork and vary widely between test providers.
What about medical predictions? Most illnesses depend on multiple genes and other factors, which makes susceptibility difficult to determine. Take cancer. America’s National Institute of Health says consumer tests look at genetic variants that “account for only a small portion of a person’s risk of that cancer”, and “are not a part of recommended clinical practice”. Claims that DNA testing can help you select your optimum diet, or predict aptitude for particular academic subjects, are equally dubious.
People like the idea, it seems, of a scientific process that can uncover who they really are. Genetic testing is based on real science, but until firmer scientific connections are established between genes and personal characteristics, you might as well spend your time pondering the shape of your skull.•