Many of us have some Neanderthal genes. Before Neanderthals went extinct about 30,000 years ago, they interbred with humans living in Europe and Asia. Today’s descendants of those pairings inherited about 2 percent of their genomes from the big-brained hominids. A research group led by David Reich at Harvard Medical School recently completed an analysis to determine the extent and identity of Neanderthal DNA in modern-day human populations. The group found that many traits in present-day people—including skin characteristics and susceptibility to various diseases—can be traced to Neanderthal DNA. It also appears that, genetically speaking, Neanderthals and humans weren’t completely compatible. Based on the uneven distribution of Neanderthal DNA in today’s genomes, the scientists concluded that many of the male offspring of Neanderthal-human unions were infertile. In the animal world, this phenomenon is known as hybrid infertility, where the offspring of a male from one subspecies and a female from another have low or no fertility. Studying human genes passed down through Neanderthals—as well as regions of the human genome notably devoid of Neanderthal DNA—provides an increasingly complete picture of the genetic landscape that contributed to health, disease and diversity among humans today. Learn more: Harvard Medical School News Release Reich Lab