People who sign up for genetic testing from companies like 23andMe can find out how much of their DNA comes from Neanderthals. For those whose ancestry lies outside Africa, that number usually falls somewhere between 1 percent and 2 percent.

Scientists are still a long way from understanding what inheriting a Neanderthal gene means to people. Some Neanderthal genes may be helpful — improving our defenses against infections, for example — but other bits may leave carriers slightly more prone to certain diseases.

On Thursday, a team of scientists revealed that two pieces of Neanderthal DNA may have another effect: They may change the shape of our brains.

The study, published in the journal Current Biology , wasn’t designed to determine how Neanderthal genes influence thought — if they do so at all. Instead, the value of the research lies in its unprecedented glimpse into the genetic changes influencing the evolution of the human brain.