LOTHARIOS everywhere will be pleased to hear that monogamy does not appear to be a natural human state. That, at least, is the conclusion of a study conducted by Michael Hammer at the University of Arizona in Tucson, and just published in Nature Genetics. By examining the DNA of living people, Dr Hammer and his colleagues have found that far fewer men than women pass their genes on to subsequent generations. In short, a small number of men have been putting it about a lot, thus outcompeting their lesser rivals.

The researchers draw their conclusion from differences between the variability of mitochondrial DNA (a type of DNA which follows the female line) and Y-chromosome DNA (which follows the male line). They examined the mitochondrial and Y-chromosome DNA of three widely separated populations—the Khoisan of southern Africa, the Khalks of Mongolia and the highlanders of Papua New Guinea—to see how those DNA sequences differed between the groups. What they found was that there is a lot of variability in the mitochondrial DNA, and much less in the Y-chromosome DNA.

The most plausible explanation for this is that a few men in each generation contribute the bulk of the Y-chromosomes to the next. Indeed, the sums suggest that, over the years, half as many men as women have passed on their genes. This news will not surprise biologists. Although a moment's thought shows the old canard that males are actually, on average, more promiscuous than females cannot be true (since every reproductive act involves one of each) biologists have known for a long time that in most species males want to be more promiscuous than females. What holds them back is that females are choosy. And females also tend to be similar in their tastes, which means some males get chosen far more often than others, and therefore have more offspring. Females, by contrast, tend to have about the same number of offspring each.

One result which did surprise the researchers was that men's genes tend to travel farther than women's. Some 70% of the world's modern cultures practice patrilocality—in which a woman moves from her native village to her husband's village when she marries. Until now, it has widely been assumed that this practice would result in women's genes migrating farther afield than men's. So, not only are fewer men than women procreating, but they are travelling farther to sow their oats. Clearly, the tall, dark stranger from another place has been an attractive proposition to women for quite some time.