Around 60,000 years ago, modern humans left Africa to begin exploring other continents. Along the way they met other early humans, such as Neanderthals, and the different species periodically bred together. Scientists have known this for a few years—there's evidence in our DNA, of which 1.5 to 4 percent in modern Europeans is Neanderthal (it's even higher in people from other parts of the world--people from East Asia have 20 percent more Neanderthal DNA). But scientists never knew if those bits of genetic code had a lasting effect on our health. After analyzing specific parts of DNA in 28,000 people, a team led by researchers at Vanderbilt University discovered correlations between Neanderthal DNA and 12 different health conditions, including depression and disorders of the skin and blood. The researchers published their work today in the journal Science.