In recent years, millions of people have been astonished, even thrilled, to learn from those popular genetic tests that their DNA is laced with Neanderthal genes.

Those genes were first discovered in 2010, in a study of Neanderthal fossils. From DNA recovered from the bones, researchers deduced that modern humans interbred with Neanderthals some 60,000 years ago, after leaving Africa.

As a result, the genes of non-Africans today are 1 percent to 2 percent Neanderthal. People of African ancestry, it was thought, have little to no Neanderthal DNA.

Using a new method to analyze DNA, however, a team of scientists has found evidence that significantly reshapes that narrative.