Ah...busy with other things, and Evolgen pounced on this story of hybrdization in the midst of the split between the pre-human and pre-chimpanzee lineages 5-7 million years ago. Carl Zimmer offers some social perspective, while John Hawks tears into the science (tears, cuts and bludgeons, actually). I don't know about the details of the science here, there is a lot of exciting hype. Talk of human-chimpanzee hybridization is trangressive and appeals to our folk mythologies of man-apes. I also know that only one chimpanzee fossil has been recovered, and the pre-Australopithecene history of own lineage is rather sktechy and spotty. The "Out of Africa" debate should make us cautious about inferring carelessly from the genetic data. Nevertheless, this paper does reemphasize our fascination with the topic of human-non-human chimeras. Last year I took issue with this passage in Jerry Coyne and H. Allen Orr's Speciation:
...Wilson et al. are probably correct in their main conclusion: although some distantly related species of birds can produce viable hybrids despite more than 15 millions of divergence (Price and Bouvier 2002),
it is absurd to suppose that equally old mammalian species (e.g., humans vs. gibbons), could yield the same result
....
Why absurd??? I was shocked by this assertion in Coyne & Orr's book because of their repeated injunction toward readers and other biologists to be cautious about generalizations and inferences based on intuition, basically, expressions of absurdity! I wrote that post before I saw this takedown of spookery by Jerry Coyne, he is certainly one who has no patience with the weaknesses of the common man and their need to populate the universe with demons, beneficial and malevolent. But when one holds other human beings to high standards of rationality and demands that they draw back from their animal intuitions, then one sets oneself up to be judged by that same standard. A belief that human-gibbon hybridization is "absurd" is not in the same league as belief in the reanimation of a dead being, no. But I think that it highlights the reality that even scientists have a difficult time breaking free of homocentrism and establishing a state of epoche in their minds, emotional detachment and analysis, when the subject is our own species. There are scientific reasons why hybridization is difficult in mammals, Greg Cochran pointed out to me that placenta are a bigger immunological hurdle than most taxa throw up. That being said, tigers and lions can give rise to fertile offspring, and their own separation seems to be on the order of ~ 2 million years, a closer relationship than we have to any extant primate, but not an order of magnitude closer. Since I originally took a interest in this issue I was witness to exchange between a group of young graduate students in developmental biology and an old bull, 30 years in the biz. They were discussing a paper on chimp genomics, and someone joked about the idiocy of hybridization. The old bull put on a serious face, and proceeded to elaborate step by step how he would go about producing a chimp-human hybrid! His opinion was the main barriers were proteins produced by the eggs of both species in relation to the sperm of the other, that is, "normal" fertilization would never be possible. He offered that artificial insertion of genetic material into the egg would do an end around this problem. Aneuploidy (uneven numbers of a chromosome) would probably result in sterile hybrids, if they were produced, but, he also stated that given enough crosses one might produce individuals who were not aneuploid, and so a hybrid population that is self-perpetuating. Now, at this point I joked that this all seemed rather worked out in his head, the old professor smiled and said he was extrapolating from fish. That's a fair enough point, and the reason that it's fair enough is that humans are animals. Yes, I think we're special in some ways, but fish, and plants, might in the near future be able to tell us a lot more about our population genetic dynamics and our deep time history than we currently assume.... Addendum: Yes Evolgen, aneuploidy might not be an issue, I'm just repeating what I heard!
