Modern humanity's ancient cousins, the Neanderthals, lived in small groups that were isolated from one another, suggests an investigation into their DNA. The analysis also finds that Neanderthals lacked some human genes that are linked to our behavior. (Related: "Why Am I Neanderthal?")

In recent years, experts in ancient DNA have mapped out the genes of Neanderthals, a species of human that vanished some 30,000 years ago. These gene maps have revealed that many modern people share a small part of their ancestry, and a small percentage of their genes, with those early humans.

Now moving beyond ancestry, researchers are comparing these ancient gene maps to those of modern humans. The comparisons may point to genes that make us