Neanderthals (or Neandertals) are our closest extinct human relatives. Neanderthals’ appearance was similar to ours, though they were shorter and stockier with angled cheekbones, prominent brow ridges, and wide noses. Though sometimes thought of as dumb brutes, scientists have discovered that they used tools, buried their dead and controlled fire, among other intelligent behaviors. It is theorized that for a time, Neanderthals, humans and probably other Homo species shared the Earth.There's much debate regarding why Neanderthals went extinct some 40,000 years ago. It was once believed that modern humans killed off the Neanderthals in a mass genocide, which doesn't make us seem very nice. Others, though, think they simply died out because they couldn't keep up with our superior hunting techniques (for instance, we had dogs).A third theory is that we absorbed the species into our own through cross-breeding. It has been estimated that 1 to 4 percent of the DNA of Asian and Caucasian Homo sapiens were derived from Neanderthals and not from modern humans. So next time you call someone a Neanderthal, just know that the Neanderthals weren't no bozos.