This is not intended to be a loaded question. I absolutely believe in evolution, and do not question that. I will be honest, I was having a conversation with a friend about the X-men, and it made me realize I don’t actually know what separates the stages of human evolution. A cursory google search says a lot about behavior, but I feel like there must be something about physical involved, as well. So what are the criteria for something to be one stage of human evolution, versus another?
In: Biology
Evolution doesn’t proceed in stages – that’s just academic categorization that we impose on nature when we classify and study things. Breaking things into stages helps us organize and research but you have to be careful not to let the artificial stages be anything more meaningful than somewhat arbitrary lines we draw.
Evolution proceeds in fits and starts, with “branches” shooting off all the time. Most of those branches wither and die out immediately, a few last a little bit and when one is successful, a new species takes root. But even then, there’s no real bright lines. Nature and evolution are hazy, more like a shrub tangled up with vines than a solitary tree.
All that said, we tend to characterize hominid species by cranial cavity size (which presumably relates to actual brain size), skull shape, dentition, how upright they stood, etc. But there’s no real linearity to human evolution – our ancestors didn’t follow a straight path from one hominid species to the next to the next and so on. Rather, for most of hominid evolution, there were likely (very likely) various species of hominid on the Earth at the same time, some capable of interbreeding successfully. It is only in the last 300 centuries or so that one hominid species came to dominate and wipe out all others.
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