Help me out, evolutionary theorists. I’m a bit puzzled at the conclusion that homo habilus cannot be ancestral to homo erectus because the two species apparently lived alongside each other for 500,000 years or so.
Isn’t it possible for one population of a species to be isolated from other populations because of relatively short-lived changes in geography or environment and to diverge just enough in that time period that speciation takes place? And after that the two populations co-habit again, but rarely or never interbreed?
With hominids, it even seems possible for me to imagine that something we could broadly define as “culture” playing a role in this kind of isolation. Reading the work of some primatologists, it seems to me that even chimps have culture in some sense, that particular social groups of chimps may have distinctive habits and practices whose roots are at least somewhat arbitrary rather than specifically adaptive. (E.g., one day an influential member of one group starts doing a common task a different but basically equivalent way, and the others eventually follow.) Exaggerate that aspect even a little bit and maybe you could get two groups of habilis living near to each other who rarely if ever interbreed simply because their day-to-day routines were culturally different, because the temporal organization of their lives amounted to the isolation of their populations from each other.
There are so many just-so stories that strike me as reasonable about the evidence that we have. As an outsider, I’m always a bit surprised at final and direct claims from the big players in the study of hominid evolution after significant fossil or genetic evidence comes to light.