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Futuyma’s Evolutionary Biology (1998): “Species are groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups”.
The “reproductive isolation” can be genetic (non-fertility), geographic, or behavioral; there is NO criteria that says (as is commonly believed) that if two populations can interbreed they are the SAME species.
YET, in attempting to refute my view (that the Ngandong skulls represent hybrids between erectus and sapiens) he characterizes THAT as int ER-species gene flow, as if it were not exactly what his own theory implies. Consider that wolves and coyotes have been distinct species for nearly a million years, or more than 300 thousand generations.
Then to further obfuscate, he plays the race-card, saying my hypothesis, “raises the specter that some populations will be seen as differing because they have more genes from an extinct species”. A similar number of generations would take the human ancestry back nearly to the last common ancestor of Homo and Pan.
BUT, those recent skulls are the very ones I contend are hybrid specimens!
Rightmire excludes the late, Southeast Asian skulls from Ngandong for very good reasons, and shows that the rest of the series reveals NO statistically significant development toward becoming modern human.
So, nearly everybody agrees that erectus could interbreed with sapiens: multiregionalists, afrocentrists, and even me.That is even with including later, African skulls that I think show some interbreeding with sapiens radiating out of Eurasia. So, the real difference in viewpoint is whether: 1) erectus evolved into modern humans by a gradual process, with int RA-species gene flow (whether it occurred only in Africa or also elsewhere) or 2) erectus and sapiens interbred, founding some (tropical) modern populations, while Eurasian sapiens founded Eurasian populations, which is my interpretation of the data.When you get up to the recent African material, which shows significant sapiens influence, the afrocentrists claim those aren’t erectus, but ‘early sapiens’. None of these views preclude interbreeding between erectus and sapiens, and the multiregional position DEPENDS on it. As a multiregionalist, he argues that “gene flow” (interbreeding) between advanced populations (who are called sapiens because of their clearly more-modern morphology) and less-advanced (erectus ‘grade’) specimens caused all the world’s ‘people’ to evolve into sapiens. sapiens could interbreed with erectus, then they should certainly have been able to produce fertile offspring with other sapiens, such as H. heidelbergensis, which may have been a direct ancestor.However, it appears they have been distinguished by neoteny: ancestral forms were succeeded by juvenilized versions of themselves.While the effects of neoteny (such as increased intelligence, delayed maturation, progressive gracilization, and a diminution of some ancestral-adult characteristics) may be profound, the genetic changes are subtle.