Tuesday, August 25, 2015
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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Common ancestors

Ardipithecus is too interesting to fight over

I spent an afternoon this week getting a personal tour of a cast of the skeleton of Ardipithecus from Tim White, the leader of the team that decsribed it. Call me a nerd, but I found it spine-tingling to hold in my hands the skull of a 4.4.million year old creature that might be very close to my own ancestor.

But it was the details that stole the show. The lack of sharpening on the rear of the canines (unlike a chimpanzee), the flared pelvis of a regular biped, the curved but relative short metatarsals of the foot, the hints of very little sexual dimorphism.

The ecology, too, is intriguing. The Afar depression was not such a depression then, and the weather was sufficiently damp for a fairly rich forest to be growing there, albeit with patches of grassland. By far the commonest antelopes were woodland-dwelling, browsing kudu. Ardi herself ate fruits and nuts from trees, not grasses -- this can be decided by isotopic analysis -- and she was a good climber as well as a walker. Her molar teeth had not grown robust like those of Lucy, for grinding grass seeds and roots, but nor had they shrunk for processing soft fruit as those of modern chimpanzees have.

Nobody quite knows where it fits in the family tree. White reckons it post-dates the split with chimpanzees and lies on our line, because it had features shared with human beings that chimps lack -- it was a good biped for example:

Ar. ramidus indicates that despite the genetic similarities of living humans and chimpanzees, the ancestor we last shared probably differed substantially from any extant African ape. Hominids and extant African apes have each become highly specialized through very different evolutionary pathways.

Others argue it might pre-date the split, on the grounds that the molecular clock points to a divergence at around 3-5 million years ago. This disagreement has already grown quite testy, though I cannot really see why: it just seems to be the pattern in academia at the moment.

White has also been sharply criticised by primatologists, some of whom hate his conclusion that chimpanzees have done a lot of evolving since the split -- or to put it another way, that in certain features the last common ancestor resembled us more than it resembled chimps. This -- to me obvious -- point upsets them because they think it undermines their claim that studying and conserving chimpanzees is justified as a study of what our ancestors must have been like.

That's weird. Study chimps to find out what a modern ape does, not as a form of self-obsession. Conserve it because it is rare, beautiful and fascinating, not out of narcissism.

Ardipithecus is a wonderful glimpse of the past. It's somewhere pretty close to the missing link, and it's interesting in its own right.