In the comments below there is a discussion about whether personhood is a continuous or categorical trait. I lean toward the former proposition as a matter of fact, but let's entertain the second. What if personhood, and in particular consciousness and moral agency, emerged repeatedly over the past two million years in singular individuals? A model I propose is that the reason that 'behavioral modernity' exhibited such a long lag behind 'anatomical modernity' is that the first conscious human kept killing themselves. After all, imagine that you come to awareness and all your peers are...well, 'dirty apes.' You are literally the sane man in the asylum. This is similar the idea proposed, reasonably enough, that a demographic 'critical mass' was required for cultural evolution to truly enter into 'lift-off.' In any case, perhaps ~50,000 year ago a psychopath was born who could live with the knowledge that their days were to be spent copulating with and eliminating with animals. Animals whom said psychopath could congenially manipulate to increase their own fitness. No sensitive soul, he. Ultimately obviously my hypothesis is far more science fiction than serious model. But it does get to the heart of something critical: the essence of humanity is not our rational reflective individual faculties, but our powerful social awareness and need for embeddedness. Even a misanthrope like me can recognize this. By our negation of it we recognize that which is the standard. Consciousness and self-awareness did not explode into the world like a shot in the dark in the form of the original human. Rather, groups of proto-humans through their collective actions stumbled upon the configuration of characteristics which connote to us humanity. There was no sentinel, only the passage of countless generations, melting unto each other.