Monday, October 5, 2009

Ardipithecus ramidus

In 1994 remains of a previously unknown hominin species were discovered in Ethiopa. This is common enough in palaeoanthropolgy- in the areas of Africa which have a geological history conducive to the preservation of fossils (mainly Ethiopia, Tanzania and part of S Africa) new remains are discovered fairly regularly. The find named Ardipithecus ramidus consisted of a few teeth, which were quickly analyzed and which suggested a new genus, and an unusually complete skeleton, poorly conserved, which Tim White has been working on for 15 years. He has now published his results, which is what everyone is excited about.

We can be certain of several things, vg: the press will make a complete mess of trying to explain it to the public, since they are looking for a story to tell, and there is no story, only a series of facts which suggest other possibilities, attempts to fill in the gaps, and at the moment the story of human evolution is mostly gaps;

there will be people who say, 'look, they don't know, they admit they were wrong.' To most people, belief is more important than knowledge, and truth means what they believe to be, rather than what is. To many such people, the knowledge that our understanding of human development has changed will come as a great relief, as they will feel justified in inventing a story of their own, or borrowing someone else’s that they happen to like;

there will be many, the great majority in all probability, who have no interest in the subject whatsoever;

there will be some who will take what understanding that can get of the subject and will then bore people senseless at every opportunity, with greater or lesser precision and powers of exegesis. Your humble blogging hedgehog is in this last category. Be warned.

So how has the analysis of Ardipithecus changed our knowledge of the subject? Well, if you really want to know, the best place to go is the original papers published by the team that is working on the bones. Registration is free and easy, and worthwhile if you have more than a passing interest in the subject. Here, here, here and here you will find experts summing it up, criticising, interpreting, suggesting new avenues of research and generally mulling the whole thing over with an expertise I cannot hope to match.

But briefly, Ardipithecus ramidus had abducting halluxes- opposable big toes- which suggest it climbed trees using all four limbs. But the pelvis and the craneum strongly point to its being bipedal on the ground. It didn't walk like apes do now. Since it comes from fairly near the chimp-human split, this suggests that the last common ancestor might have had a locomotion more similar to ours than to modern apes. It appears, from this and other characteristics, that chimpanzees and gorillas may have evolved much further from the LCA than was previously thought. They might, in fact, have evolved further than we have ourselves. It is this aspect of the work that is going to bet the press and the public excited, and it is what will most impinge on our understanding of ourselves.

There'll be plenty more in the next few weeks. Watch this space. Ot click the links.


Vincent said...

"They might, in fact, have evolved further than we have ourselves."

This is a bombshell, if I understand it correctly. You are suggesting the possibility that we, homo sapiens sapiens, have evolved from LCA with fewer steps than chimpanzees and gorillas? You are talking presumably about DNA - that ours is more similar to LCA than theirs? In which case how do we know that the LCA was indeed the LCA.

I'm asking you because you appear to have a grasp of this and no interest in being gratuitously sensationalist.

But I suppose I have to follow your links too.

CIngram said...

My interest is great, my 'grasp' rather less so. The chimp-human split is calculated at 5-7 million years ago, by a combination of various methods, including a fair amount of guesswork. Apart from a couple of incomplete crania, the oldest remains in the human line are those of Australopithecus afarensis (Lucy), just over three million years old. That's a huge time gap.

There has long been an assumption, based on the (scarce) available information, that the LCA was something like a chimp, and specifically that it moved more or less like chimps and gorillas. Ardipithecus is 4.4 million years old and it looks as though that assumption needs to be re-evaluated. In that sense it is indeed a bombshell.

Its not about DNA; at that timescale there's nothing left you can analyze. But the morphology was expected to be much more ape-like than human-like, and it now seems that this may not be the case.

You do need to follow the links, really. This is an excellent place to start, and this and especially this are the most relevant papers from the researchers.