The DNA clock revisited:
Many years ago while job hunting I was chatting with a radiologist who confided in me that one of the partners was in a wine tasting club. They would get together and share out a bottle and each have a sip. Hereupon his narrative segued into drama and he indicated taking a small amount with a very intense look and saying things like, “Yes … rather smooth in a tart sort of way … sort of oak and fruit … nice finish … good legs … no I meant the girl … yes, that’s wine all right.” It’s easy to mock anybody with a passion, particularly an expensive passion. Yes, I have a passion about my subject of fertility and kinship, so have at it; I can take it.
Among the passionate of the earth are paleontologists. They look at old bones and related things. And sure enough they gaze and gaze and come up with opinions, which once formed are defended with zeal. Every nuance is treasured. There are, in fact, so few bones of primates closer kin to us than chimpanzees that you could toss them all in the back of a pickup truck. But with much study and deep thought the experts, clad in cargo pants and long sleeve shirts, I imagine, with mosquito netting on their pith helmets and wool socks within their heavy shoes, have slowly been putting together a story of our prehistoric events.
Enter genetic analysis. Kaki gives way to starched while linen lab coats. The sundown Scotch is replaced by fresh squeezed fruit juice. The cigar yields to air. Armed with information about the genes of different animals and with an idea about mutation rates it became possible to estimate how long ago two species had separated.
And of course when you get new information about a system that you really don’t understand it conflicts with what you thought you knew. And so the punch up went on for years, the bone folks and the Pyrex glassware folks each regarding the other as in profound darkness.
Well there’s news. (Ewen Callaway Studies Slow the Human DNA Clock NATURE vol. 489 no. 7416 September 20, 2012 page 343 and Ann Gibbons Turning Back the Clock: Slowing the Pace of Prehistory SCIENCE vol. 338 no. 6104 October 12, 2012 page 189) At least they told us about it. They aren’t too bad at that. The things that go unheralded are terminology changes like sea star for starfish and Chron disease for Chron’s disease. I suppose they know they could never withstand the public outcry, so they just slip those past us.
Well the news is that the DNA evidence was calibrated wrong. The mutation rate is now thought to be less than half what it was thought to be. And since in males the mutation rate is higher than in females and since at least in humans (and from what I can tell among our ape cousins as well) older males are relatively successful at attracting mates and since older males have even more mutations per generation than younger males (It has to do with the fact that sperm are always being replaced but ova are all made in utero and are in a sort of deep freeze most of the time.) the situation is actually worse.
So whatever date you have been given for an old bone, you can more than double it if the dating was done by DNA analysis but not if it was done by dating the geologic stratum in which it lay assuming it didn’t fall down a hole or something.
So in case I haven’t recently retracted everything I ever said about prehistoric ancestors, let me retract it all now. It’s not like it ever went together into a consistent picture for me anyway. This change doesn’t bother me as much as others.
Oh let’s take for instance the notion that the Mediterranean Sea was a salt desert five million years ago when water started pouring through what is now the Straights of Gibraltar. It used to be about the time when humans split from Chimpanzees. It shouldn’t have anything to do with us. No racial memory of that. The sea floor is about a mile down, and so is the Nile valley although of course it is silted up so that it is farmable. We never had to cross that valley with its possible weird dangers; if you go down a mile below sea level the air gets so dense (and I mean free air, not a diving bell with compressed air) that almost anything can fly. Let your imagination rip, but it didn’t involve us. But now it does. Evolution had gone most of the way to making modern humans. We just might have a clue that things can get very bad Down There.
Or take the split between humans and orangutans. It used to be about 13 or 14 million years ago. All right. That’s a long time but not really a problem. But now the split may be as far back as 46 million years ago. Now arguably that common ancestor was fairly close to an average of a gorilla, a chimpanzee, a human and an orangutan. A pretty big guy in other words.
Now we have been told that at the time of the dinosaurs mammals were little rat like things that scampered around trees snatching insects. So how long had that common ancestor of all great apes been around? Its progeny changed substantially be can be recognized after at least 46 million years, so it is no great stretch to say it had been around something like 20 million years before the split and the split is probably even farther back than they are saying; let’s say split 50 million years back, first great ape that you would recognize to be a great ape 70 million years ago. Of course there is absolutely no fossil record (wait for it) to suggest that. But remember that pickup truck. A lot of things can fail to show up in the fossil record.
Dinosaurs were still around until 65 million years ago. So great apes would have been living among them. That’s conceivable. A great ape would have been a tasty snack for a carnivorous dinosaur. You wouldn’t want to go up with one yourself without a weapon and a primitive weapon either is a rock or needs a shaped rock to be manufactured; that would have shown up in the fossil record for sure. So the obvious strategy would be to go up a tree, something that apes are good at.
Look into the eyes of an orangutan, a chimpanzee or a gorilla, or a human teenager lots of times, and you get the message, “Yeah, sure. Look. This is no big deal. Let me know when something important happens.” Contrast that with the bright, inquisitive look of a monkey or lemur. They look as if life is scary. Everything is important.
Spend a couple of million years being treed by tyrannosaurus and see whether life doesn’t seem a bit dull after that. After all, that big lizard just might be able to push your tree over.
So what to do. Everybody knows. You run. You run like the wind. You run and duck and cover and jink and run some more. But apes are poor runners. It’s human who are brilliant runners. We are the best. Our feet don’t grasp well, but they really let us haul our butts. So the evolutionary pressure was on to develop the heel. Wings evolved more than once, why not heels? So there was reason enough, using the revised chronology, for apes to develop heels. And we know it was possible because we have heels.
So the droll fantasy emerges of the bit of petrified mud that has dinosaur footprints in pursuit of human looking, although obviously not otherwise human, footprints. Any professional paleontologist would toss it into the trash for fear of being thought mad.
Of course I am not proposing this. I am just pointing out that when they start changing the rules that much things get crazy.
I know I just retracted anything I ever wrote about prehistoric ancestors. It’s time to do it again.
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