The Descent of Man

In the beardy chaos of non-parsimony, at least two theories about our human origins are competing for your attention. Let’s leave creationism out for the moment — that one is old, and has been debunked by better men. (Not to mention, its proponents do a pretty good job ridiculing their ideas themselves.) Fortunately, even while embracing evolution there is enough room for hairy theories. And what is a more engaging subject for such theories than our own evolutionary past?

Theory I: the pig+chimp Pimp theory
Geneticist Gene McCarthy specializes in hybridization, and as such has started seeing hybrids everywhere. That happens, we all know it does. You spend the day dissecting larvae, and on your way home even the trees start to look like imaginal discs. But I digress.

The point is: Gene McCarthy, PhD, knows a hybrid when he sees one. In the mirror, for example: humans, McCarthy says, are clearly a product of hybridization. As he’s a geneticist he must have genetic evidence for this theory, right? Well, no—but he won’t let that spoil the party. Making anatomical comparisons will get you a long way, and so he listed all the traits that us humans have that can’t be found in our closest living relatives, the chimpanzees. Think earlobes, thick skins, and hairlessness. From that list it was evident who the co-parent must have been: the pig.

Yes, he’s serious, and he has a lot of ideas about how that hybridization event could have come about. Rule 34 comes to mind, and I need to change the subject now.

So let’s talk about genetics, McCarthy—you must have something, right? Why yes, he has an excuse: the original hybrids must have been backcrossed to one of the parent species, and diluted any genetic signal from the other parent. Furthermore: “Sequence differences are not necessary for anatomical differences to be present”. Well that solves that puzzle.

But what of the idea that we’re hybrids at all? For this premise, McCarthy presents the dead giveaway: human infertility. With a population over seven billion that too seems a bit of a stretch, but let’s here the man out. On his site McCarthy details all the ways in which our spermatozoa are incompetent little bastards. And the logical steps from ‘our sperm sucks’ to ‘we’re practically infertile’ to ‘must be ’cause we’re hybrids’ follow easily.

To recap: humans are infertile, we share traits with pigs, and many backcrosses will have got rid of genetic evidence. Take away Occam’s shaving implements, and the case is clear-cut. (Sadly, some popular press seems to actually think so…)

Theory II: Homo aquarius
Our surprisingly hairless skins inspired more than just a reminiscence of porcine ancestors. Together with our bipedalism, the blubbery fat under our skins, our big brains, and—only added recently—our large and empty sinuses, they provided evidence for another theory about our forefathers: they inhabited beachfront property.

The aquatic ape theory, as it is called, was first coined in the 60s by Sir Alister Clavering Hardy, marine biologist (I’m sensing a pattern here). Subsequent exploration proved an entertaining exercise: pick a human trait, and try to link it to an aquatic environment. Even better if it’s a trait that can’t be detected in fossils.

Of course you can do the same thing with basically any other hypothetical environment, but where’s the fun in that? (Actually, I was joking: there is a lot of fun in that.)

You know what: I think I get it. If you’re hairless, you don’t need a razor. It all makes sense now.

Photo by cdorobek, licensed under creative commons.

2 thoughts on “The Descent of Man

  1. “A frightening amount of serious scientists seem to be following @Macroevo. ” Message from the English Grammar Police. Use “number” with count nouns (like scientists) use amount with mass nouns (like butter or rice). (And I’m also sorry you find my success so frightening.)

    I’d like to say, too, that if you’re a scientist (I’m not sure that’s the case since I’ve never heard of you) or even a aspiring journalist, you really shouldn’t quote out of context. For example you shouldn’t quote me as saying “Sequence differences are not necessary for anatomical differences to be present,” when what I actually say is “Sequence differences are not necessary for anatomical differences to be present. An obvious example of this phenomenon is Down’s syndrome. Individuals affected by Down’s regularly exhibit certain distinctive anatomical features, and yet in terms of their nucleotide sequences they do not differ in any way from other humans. To detect someone with Down’s syndrome, sequence data is completely useless. But with anatomical data, detecting affected individuals is easy.” I’ve got a PhD in genetics and all the statements just quoted are true. What I’m explaining there is that anatomical differences can arise as the result of dosage differences (changes in gene counts), even when there are no changes in actual gene sequences. It’s really so lame and lazy (and, if you understood my point, underhanded) of you to set up a straw man in that way and misrepresent my argument. I’ll give you the benefit of the doubt, though, and just assume that you have no background in genetics and were simply unable understand what I was saying. I’ll finish by saying that with me you have nothing to fear, not unless you’re afraid of documented facts and honest opinions.

  2. Hi Gene, thanks for the language police comment! I had noticed my mistake, but too late; very ironic as this is one of the commonly made mistakes that I frequently correct others on in my native language.

    Of course I’m not really frightened by the amount of twitter followers you have; that was an embellishment. But it did strike me as odd that so many of my colleagues follow you, as I find it so hard to take your theory seriously. So my question was genuine: am I missing something? Or did they 1. not care; 2. not see your theory yet; or 3. decide to keep following you for the entertainment value?

    I am well aware that sequence data is not everything; e.g. developmental plasticity and epigenetics are very powerful forces that can translate identical genomes to vastly different phenotypes. (I don’t think your example of Down’s syndrome is particularly well chosen, as there is a whole extra chromosome involved — that seems like quite a genetic change to me!) However, I’m not so sure this is a good argument to be made as a rebuttal for the fact that there are no genetic indications that humans have such a recent porcine ancestor. Assuming this hybridization event indeed took place and contributed to the current species, then the way in which it would have contributed would be by leaving genetic material, would it not? If we inherited these characteristics from pigs, as you hypothesize, what else could have maintained them in our population for so long but genetic information? Or do you assume extremely well-maintained epigenetic markers here?

    The reason you find yourself on this blog is because in my opinion the Pig-Chimp hybrid theory is a great example of using real data, but an outlandish explanation for that data. Or: not applying Occam’s razor, which is what our project is all about. Of course Occam’s razor is not flawless; while it is an important scientific principle it can of course be wrong. I wonder how you feel about this; do you think you’re applying it and I’m misjudging? Do respond, I’m curious.

    Best, Barbara

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