I’m not sure what the point of this post is, I’m just kind of thinking out loud and I’m sure that those who know a lot more about genetic analysis will be able to point out some errors in all this, but hey, live and learn.
I’m sure my readers remember the paper that suggested some chimp/early hominin hanky panky? I bring this up because I am currently reading The Emergence of Modern Humans: Biocultural Adaptations in the Later Pleistocene. The book is a collection of essays based on a symposium called ‘The Biocultural Emergence of Modern Humans in the Later Pleistocene” held in 1986.
One of the participants at the symposium was Milford Wolpoff and his essay is quite interesting. In one part of that essay, Wolpoff talks about the use of mtDNA to provide evidence of hybridization among a wide variety of different species (deer, mice, etc.) including chimps and early humans. For this he sites a 1985 paper called Dating of the human-ape splitting by a molecular clock of mitochondrial DNA which suggested that interspecies transfer of mtDNA occurred between chimps and early humans – and specifically suggested that the transfer was from chimps to humans. Obviously then, the above paper by Patterson et al didn’t really contain anything new, it just approached it from a different direction.
Wolpoff brings this up in the context of the effect of interspecies transfer of mtDNA on the calibration of dates of splitting (i. e. the timing of mitochondrial Eve), but this made me wonder. If the analysis of mtDNA reveals a lot of hybridization (in addition to Wolpoff’s examples a quick Google search also mentions a wide variety of plants, wolf/coyote, and cattle) I have to wonder when this stopped in primates? If Hasegawa et al and Patterson et al are correct, then, say, interspecies gene transfer occurred between chimps and Australopithecines (or maybe Ardipithecus ). Looking from the other direction, and ignoring some of the recent research on introgression, anatomically modern humans and neanderthals were, it is claimed, incapable of forming hybrids. So some time between a couple of million (if we accept the above two studies) and a couple hundred thousand years ago (e. g. around the time of Herto) something happened to change things. But then, maybe I am reading too much into too little…