Carolyn Y. Johnson writes:

For most of our evolutionary history, humankind was made up of many human kinds.

Take the last 100,000 years or so. The oft-caricatured, big-browed Neanderthals roamed across Europe and into western Asia. The mysterious, towering Denisovans hunted and gathered in Asia. The diminutive, hobbit-like Homo floresiensis dwelled on an Indonesian island. The last of Homo erectus had just died out in Java. Our species, Homo sapiens, was merely another variation on the type.

It’s tempting to assume the monolithic human world we live in now is the normal one. But for many scientists who study the ancient past, the present is the puzzle.

“This is a strange time,” said Chris Stringer, a paleoanthropologist at the Natural History Museum in London. “Why are we the last ones left, and what happened to all the others?”

For decades, humanity’s narrative of its own origins was intertwined with presumptions of biological exceptionalism. Human evolution was often portrayed as a march toward the big brains, adept tool use and social complexity of modern day people.

In that story, the other hominins — human ancestors and evolutionary cousins — were primitive discards. They deservedly died out. We were the happy ending.

“Everything else was brutish,” said Eleanor Scerri, an archaeological scientist at the Max Planck Institute of Geoanthropology, reflecting on the ideas that dominated discussions of human evolution in the 1980s, when as a child she first became hooked on the field. “That was very much in vogue: ‘And we survived, because we were the greatest.’”

Over the course of Dr. Scerri’s career, however, the story about human origins has been rewritten and revised, as new lines of evidence have emerged. That includes the narrowing of the cognitive gap between Homo sapiens and our close cousins, with evidence that they also had sophisticated abilities — to make art, bury their dead and wield fire. Still, there are now more than eight billion humans on the planet, of only one type.

Amid the daunting saga that is human evolution, the Neanderthals, so recent and closely studied, are in many ways the accessible celebrities of the story. Their fate seems to offer a toehold on the big questions about how we came to be the last species standing. What happened to the Neanderthals, then?

One glib answer is that they are still here, lurking in the DNA of present-day people in tiny amounts. Ancient DNA studies revealed that Neanderthals and Denisovans, and possibly others, didn’t so much as die out as become absorbed, through mating, into who we are today.

But if it were possible to ask Neanderthals, they probably wouldn’t see themselves present on the planet. So why are modern humans alone now? How much of our success stems from unique abilities? How much of our advantage was just luck? Can the past teach us anything about how to think about the existential risks of the present and the future?

Are we triumphant survivors — or just next on the evolutionary chopping block?

Picture a day in the Pleistocene. A group of humans kindle a fire to cook, striking a flint against pyrite. They hunt big game. They also gather plants to eat and, perhaps, use as medicine. They draw on the walls of caves. They care for sick and disabled compatriots, even performing something like a root canal to relieve a throbbing toothache.

But “they” aren’t Homo sapiens — they are Neanderthals. [Continue reading…]