Writer Carl Zimmer did a predictably smart Ask Me Anything at Reddit, fielding all manner of queries on his forte, science. One exchange is about ancient humans, who were a decidedly more heterogeneous mix than we are, something that could again be true of our species in the future. An excerpt:

Question:

What ancient human fact do you find to be the most fascinating?

Carl Zimmer:

Can I give two answers? A tie?

First off, all the species of ancient humans! One scientist I interviewed recently said he likes to say that the Middle Pleistocene was like Middle Earth, with orc and elves and such. I guess that might be a bit strained if you consider that the different hominin species probably couldn’t talk to each other. (Imagine the Lord of the Rings movies with no dialogue…) Still, tiny Homo floresiensis, Denisovans and Neanderthals having sex (and babies too) with modern humans, plus Homo erectus and probably a bunch of other species/lineages we have yet to find. Our current loneliness is a fluke of human evolution.

The other fact is that in one respect Darwin got human evolution very wrong. He saw bipedalism and human behavior as intimately tied together. But the earliest hominins, 6-7 million years ago, were fairly upright (even if they could scale trees to get away from the occasional leopard). Despite being upright, their brains were puny till less than 2 million years ago. So for most of hominin evolution, they were essentially bipedal apes, rather than what we’d call human. Which, of course, leaves us with the question of why human brains got big so fast when smaller ones did just fine, thank you very much.•