What makes a human a human?

"Mitochondrial Eve" is about 100-200 thousand years ago in Africa. This refers to not a single individual, but a single population of perhaps a thousand or fewer individuals from whom all modern humans are descended. While some of the adaptations we see in modern humans are certainly the result of evolving to be smarter, faster, and adaptable, the fact is that your ancestors were all horribly inbred. The skull of H. sapiens is fucking weird looking. Check it out:

H. Erectus:

H. Heidelbergensis:

H. Neanderthalensis:

H. Sapiens.

Do we actually look anything like our nearest relatives? No. Because, just like in West Virginia, it's all relative in Africa 100KYA. Our reduced palette and weird shaped skull? It's probably because your ancestors were making it with their first cousins. What's the fastest way to tell if something is an anatomically-modern Homo Sapiens or not?

Well, if you've got a mandible, the question to ask is... Does it have a chin?

That's right. The fastest way to identify if you've got H. Sapiens or H. Something Else is that little buildup of bone at the base of the mandible. And where does that come from? Well, you're reducing the size of your jaw, and the bone has to go somewhere. And if you decide to move up the face, what's the next defining feature?

Anatomically modern humans have no retromolar space. While in earlier forms the jaw extends past the base of the third molar, in humans the jaw is squashed in to reduce prognathism. What do we pay for our markedly reduced alveolar prognathism? Well, if you've ever had a wisdom tooth pulled, you know - Our jaws can't hold all our teeth. We're evolving out our M3.

You know who else didn't have an M3? H. Florensiensis. "The Hobbit." An island population that, over the course of a few hundred thousand years, managed to reduce everything about itself. You know what they wound up with? Smaller jaws, no M3s, and teeth more jacked up than a Liverpudlian. (No offense to the Liverpudlians.)

So, everything that makes us human? Founder effect. Genetic bottlenecks and inbreeding.