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There are many different species of whale, bear, ant—even elephant. Why are we the only species of human? Well, as recently as 50,000 years ago, we weren't. Watch the video below to explore why our species was the one to keep on living.
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It appears that when our human ancestors migrated out of Africa around 60,000 years ago, they weren't concerned about keeping sexual relations within the species. Scientists have found that most modern Europeans and Asians have between 1 and 4 percent Neanderthal DNA, a remnant of these long-ago rendezvous. In fact, most people living outside of Africa carry a bit of Neanderthal in their genes. (People indigenous to sub-Saharan Africa do not have the Neanderthal DNA, as they did not migrate to the Eurasian landmass.)
The first time someone depicted human evolution in a horizontal sequence was 1863, four years after Darwin published "On the Origin of Species," the foundation to evolutionary biology. Darwin depicted evolution very differently, using a branching diagram that showed evolution as a complex process where no single organism is the sole descendant of any other -- pretty close to how biologists view it today. But despite how wrong it was, the simple, logical progression of the "monkey-to-man" image was more engaging. It has lived on in various forms to this day, most famously in Rudolph Franz Zallinger's 1965 illustration "The Road to Homo Sapiens." So why is it wrong? Evolution is not regular and predictable like the image suggests. It's messy, hitting dead ends at some points and turning back around at others. Perhaps evolutionary biologist Stephen Jay Gould said it best: "Life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress."
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