Humanity's evolutionary path thus far has been far from simple. It is not as straightforward as ape-like ancestor Homo sapiens. Quite the opposite, it's a complicated story of populations with various degrees of divergence and contact -- a tangled web. Despite many popular depictions, evolution does not follow a straight path. It's a meandering route of possibility, with plenty of side roads that may or may not curve back to the trajectory they sprung from.

Many people around the world have more Denisovan DNA than previously thought, which has contributed to their sense of smell and ability to thrive at high altitudes, according to a study released Monday. Researchers know that modern humans with ancestry outside of Africa inherited up to 2.1 percent of their DNA from Neanderthals. But far less was known about Denisovans, who are believed to have shared origins with Neanderthals and account for up to 5 percent of DNA in some present day populations. The latest work, from a research team at Harvard Medical School and UCLA, developed a world map of ancient DNA. In doing so, they found that populations in Oceania populations had the highest percentage of ancient DNA – 2 percent Neanderthal and 5 percent Denisovan - while South Asians had more Denisovan DNA – 0.1 percent in Sherpas - than expected.

They died out more than 40,000 years ago but the legacy left by two prehistoric species of early humans is far more widespread than had been previously believed. Scientists have discovered a surprising number of bloodlines around the world carry fragments of DNA from Neanderthals or their sister species, the mysterious Denisovans. Their analysis suggests that our modern human ancestors appear to have interbred with the Denisovans just 100 generations after their trysts with Neanderthals. Scientists have produced new maps showing the levels of Neanderthal and Denisovan ancestry around the world. And the study has unearthed some surprising new benefits these illicit encounters have gifted to modern humans living today.