For a long time, the answer seemed clear. Our species, Homo sapiens—with our complex thoughts and deep emotions—were the only true humans to ever walk the Earth. Earlier forms, like the Neanderthals, were thought to be just steps along the path of evolution, who died out because we were better versions.

That picture is now changing.

In recent years, researchers have gained the power to pull DNA from ancient hominins, including our early ancestors and other relatives who walked on two legs. Ancient DNA technology has revolutionized the way we study human history and has quickly taken off, with a constant stream of studies exploring the genes of long-ago people.

Along with more fossils and artifacts, the DNA findings are pointing us to a challenging idea: We're not so special. For most of human history we shared the planet with other kinds of early humans, and those now-extinct groups were a lot like us.

"We can see them as being fully human. But, interestingly, a different kind of human," said Chris Stringer, a human evolution expert at London's Natural History Museum. "A different way to be human."

What's more, humans had close—even intimate—interactions with some of these other groups, including Neanderthals, Denisovans and "ghost populations" we only know from DNA.