Modern humans and Neanderthals got it on with each other often enough to leave the human genome across Europe, and much of Asia was heavily laden with Neanderthal DNA. Some studies have concluded gene varieties inherited from Neanderthals are much rarer than they were 45,000 years ago leading geneticists to conclude the lost genes were an evolutionary hindrance, weeded out by natural selection. A new study suggests this isn't true, and has some further bad news for proponents of pseudo-scientific race theories.

Humans assume our superiority to our nearest relatives, making “Neanderthal” an insult. So the discovery that everyone of non-African descent carries 1-2 percent gene varieties inherited from Neanderthals (and sometimes other early humans) was a shock.

Some previous studies suggested this figure was higher 45,000 years ago. The apparent decline has been attributed to natural selection. Despite some advantages for the immune system, most Neanderthal genes were inferior, the theory ran, putting those who carried them at an evolutionary disadvantage. Not only could the Neanderthals themselves not cut it in competition with ourselves, according to this view, neither could their distinctive genetics.

Leading scholars of Neanderthal genetics have challenged this idea in Proceedings of the National Academy of Sciences. Instead of Neanderthal gene varieties being weeded out by natural selection, the paper argues, their concentration has been stable for tens of thousands of years. Those variations evolution rejected disappeared from the human gene pool within the first few hundred generations after Neanderthal/human mating, rather than in the subsequent 2,000 or so.

The conclusion is based on comparing the genomes of ancient individuals with those living people, and some advanced modeling techniques of changes over that time. Our picture of the ancient gene pool is distorted because DNA survives much longer in cold climates than hot ones, leaving us the genetic code for people living in Europe tens of thousands of years ago, but nothing similar for Africa or India.

Dr Janet Kelso and her colleagues at the Max Plank Institute of Evolutionary Anthropology argue that in the absence of knowing the ancient genomes of people in hotter climates, past models have assumed no sharing of genes between ancient Europeans and Africans.

Instead, they show, there was considerable gene-flow between these two populations. Accounting for this, the Neanderthal share of European genetics has been stable.

The finding deals another blow to claims, like those James Watson recently repeated, that there are racial differences in IQ. Intelligence is so complex it definitely evolves slowly, and 100,000 years of isolation between races is probably not long enough to produce detectable differences. The more the isolation has been broken in that time through gene flow between the populations, the more improbable it becomes for races to be genetically predisposed to different intelligences.