The More Things Change, The More They Stay The Same

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…

14 Responses

  1. Plenty of accounts of contemporary bonobos having sex with chimpanzees, despite 3 million years or so of being seperate species. No guarantees of sucessful reproduction, of course, just sex — but it does make believable the notion of similar behavior amongst proto-humans and proto-chimps some 6 million years ago (or 5 million, or 4 million, or 3 million years ago, or last Thursday). And when the degree of seperation wasn’t that great, it’s quite plausible that some hybrid offspring would have been produced. Enough offspring to show up in modern day mtDNA analysis? That I can’t say.
    Probably, we should have considered the possibility of homo-pan hybridization more explicitly long ago, but it sort of goes against the anthropological grain. We’d like to find simply drawn lineages in the past, and allowing for hybridization makes things very very murky. (Need I add that physical anthropology has very Victorian roots?)

  2. “I’m not sure what the point of this post is…”
    It’s your blog! What more of a point do you need? 😉

  3. Evolution is a complicated, messy business. Wolpoff understands this, even if he is wrong about some particulars. And you can’t ignore the “introgression” issue stemming from the “modern human origins” debate that just keeps going on and on and on. At one point, proto-humans of some kind(most likely some australopith), were probably closely enough related to exchange genes. My own feeling is that later members of the genus Homo were also able to do this successfully(and yeah, that means Neandertals and “modern” humans, though these may or may not “really” be separate species in the first place) were also able to do this, in much the same way as members of the genus Canis(domestic dogs, wolves, coyotes, jackals, etc)are still able to do(and yeah, wolves x coyotes produce fertile offspring, as do certain species of gulls that commonly interbreed; where I live all the gulls here are considered hybrids of two common species). So no, I’m not surprised that still another paper on chimp/proto-human hybridization has entered the fray. It no doubt happened at one time. Then “our line” evolved fairly rapidly and the genus Homo was born. By that time, later Homo could probably hybridize with other branches of Homo, but not with australopiths, if there were any left, and certainly not with chimps. Too much evolution had been going on.
    Anne G

  4. “…anatomically modern humans and neanderthals were, it is claimed, incapable of forming hybrids”
    Not according to Wolpoff. He tours a speech entitled “The Neaderthal in your closet”.

  5. There were some pretty common criticisms of mtDNA when used for /any/ sort of evolutionary clock. I’ve heard some pretty compelling arguments that mtDNA doesn’t mean at all what some are claiming. Have these arguments been resolved recently? I can picture a certain anth professor making a face when anyone brought up mtDNA as evidence for /anything/. She was convinced the whole thing was snake-oil.
    When I last looked at this, the mtDNA argument was generating more catfights than the old splitters vs. clumpers story. Since *both* of these old arguments are under consideration for some of the work you talk about here, I assume that we don’t have much agreement at all about this aspect of human lineage.
    Still, fascinating stuff.

  6. “anatomically modern humans and neanderthals were, it is claimed, incapable of forming hybrids”. I don’t know that anyone seriously claims they were “incapable of forming hybrids”, just that they didn’t for some reason or another. After all they separated just half a million years ago and most species as closely related in time as that are quite capable of producing fertile offspring. I understand bonobos and chimps are quite capable of producing fertile offspring. It’s just that it’s discouraged in zoos because of ideas of preserving biodiversity.
    On the other hand I doubt that humans and chimps could produce offspring today, fertile or otherwise. But obviously if they spring from a single species they would have originally been quite capable of it for some time. The length of time involved would bear some relationship to the level of ongoing back-crossing. And why on earth would there not be? Unless some geographic feature suddenly rose and separated them.
    I saw a recently published book on NZ hebes (a native veronica) yesterday. The complexity is unbelievable. Do all these subtle differences really indicate separate species? Or, is the reality, as a friend of mine used to say, “There’s only five different species. The rest are hybrids containing differing proportions of them”.

  7. terryt – that is actually what I was trying to get at. For whatever reason, the Out – of -Africa group are all for replacement with no intermixture. Certainly, the recent sequencing of the Neanderthal genome gives some support for the idea. Seems to be at odds with all the hybridization going on in the rest of the animal kingdom and needs to be explained.

  8. This is precisely the aspect of the assertion that there was no interbreeding between our species and Neanderthals which always gave me the most pause. I mean, seriously — in common with much of the animal kingdom, humans are frequently willing to have sex with anything that doesn’t run away fast enough. The idea that they wouldn’t have sex with Neanderthals contradicts just so much about experience that I find it hard to accept without some damn good evidence to back it up. And since there really isn’t any evidence to that effect (that I’m aware of, anyway) we have to fall back on the assertion that the genetics were such that viable hybrids couldn’t be born…and that, as you point out, sounds somewhat dubious as well. I just don’t think we have enough evidence to make positive statements about this, right now.
    Of course, I may be biased. One of my friends from my adolescence has a classic occipital bun and brow ridges (and a slight but noticeable to the touch sagittal crest), and in our adolescent naivety we always thought she had some remote Neanderthal ancestry poking its face through her genetics.

  9. Luna —
    We need to consider social context. Historically, physical anthropology was put together by mostly white males of middle to upper class social status, most of them doing field work in the first half of the 20th century, and explaining their work in papers and books aimed at fellow professionals of similar social class. Non-professionals with an interest in the subject basically belonged (and belong today) to the same sort of people — reasonably affluent, well educated, mostly white, with “appropriate” upbringing.
    And for most of that time period, it Wasn’t Done for such people to admit in public that homo sapiens sapiens with white skins had been known to cohabit with homo sapiens sapiens with black or brown or red or yellow skins, let alone produce children. Civilized People Didn’t Do That Kind Of Thing! And they didn’t do it even in the distant past, even before civilization either!
    It didn’t occur to anyone in that group that this was nonsense. They saw it as a law of nature.
    I’m in my sixties. I remember those days. Believe me.

  10. @mike shupp — point.
    I still think it takes some serious compartmentalisation away from one’s experience of the rest of humanity, though.

  11. Luna —
    Well yes … but in retrospect, looking back 40 years, it does srike me that my parents and other folk of their generation often had to believe six impossible things before breakfast every day to make social existence possible. My high school civics class in 1963, for example, never once dealt with the issue of black boting rights in the South. It was a non-issue, and the closest we might have ever got to it was my teacher making the occasional remark like “If you get down to Louisiana, say, it’s a different place different there.” Which meant nothing at all to us nice middle class Ohio kids, all thirty of us in our all-white class in our almost all-white public school.
    So you can soft of understand, if not fully sympathize, with someone like the lake Glen Isaacs — a giant in the anthropological / archaeological field! — thinking he saw evidence in 2 million year old Homo habilis sites for hearths and the beginnings of communities and even mid-20th century American style nuclear families.
    My sneaking suspcion is things aren’t totally different today, but we wear ideological spectacles which conceal different sets of uncomfortable realities.
    Ah well! Interesting stuff but probably off topic.

  12. Mike – no, not off topic at all. Since you mention Isaac, I can’t resist mentioning a counter example in the form of C. Loring Brace – came from an upper crust blue blood family and didn’t buy into any of that…

  13. Well, yes. I can see that.
    I guess…it’s just hard to undo my own “ideological spectacles”, which these days tend to include the awareness of a heck of a lot of subculture. But it’s probably related to the beef a lot of people have with Evolutionary Psychology, isn’t it — the problem of taking one’s own cultural norm and assuming that it is a universal truth of human behavior with necessarily deep roots in ancient history.

  14. Y’all have left this fascinating topic, but I’ll put in my 2 cents, nevertheless. Despite the evidence of modern mtDNA that strongly supports the Out-of-Africa sans mixing view, there are some interesting fossils dating from the time when H. sapiens first entered Europe and Asia, described mainly by E. Trinkaus, that suggest otherwise. One comes from the Cave of the Old Woman (Peshtera Muieri, I believe) in Rumania, and one in China. In both cases, the skeleton is what Trinkaus describes as a mosaic of primitive and modern features. He plausibly hypothesizes that the reason is due to mixed ancestry. There is also the Lagar Velho boy (Portugal), only 4 years old or so and with a definite chin, a H. sapiens feature all right, but with big, massive bones like H. neanderthalensis. He dates from the Gravettian, too, about the time of the very last Neanderthals, who survived the longest around Gibraltar. Hm, so they COULDN’T interbreed? Who says? Why not? Because it would be ICKY? Because non-sapiens Homo had COOTIES? That’s what I suspect those scientists are really thinking. Because plenty of similar species actually do breed — lions and tigers; cattle and buffaloes; horses and donkeys; horses and zebras. Of course, not all similar species are successful — look at sheep and goats, so much alike that even experts can hardly tell the bones apart, but they can’t interbreed. But as Granny Mitchell used to say, “The proof is in the pudding.” And it seems that, mtDNA to the contrary, Trinkaus has found a bit of pudding.

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