You probably didn’t miss all the buzz about Ardipithecus yesterday. If you did, here’s a few links to get you started on all the press releases and blog comments:
- The 4.4 million year old Ardipithecus ramidus (Anthropology.net)
- Ardipithecus ramidus remains finally published after years delay. Not all that interesting (Greg Laden)
- Ardipithecus FAQ (John Hawks)
- Humans vs chimps — neither is an offshot (Genomicron)
- Ardipithecus round-up (Evolving Complexity)
…and that is just a start.
For the original papers, you get a list here:
- Science publishes 11 papers on Ardipithecus ramidus (Anthropology.net)
I haven’t started reading those yet — I still find paleonotology hard to read — but I am going to spell my way through them in the weekend.
From what I can read from all the second-hand comments, though, we are talking about a 4.4 mya species with lots of traits similar to modern humans as opposed to modern chimpanzee hinting that our common ancestor might not necessarily be more chimp-like than human-like.
This may or may not surprise you… That depends a bit on how special you think humans are from the African apes (chimp and gorilla). A priori, traits shared by those two and not humans are probably evolved on the human lineage rather than independently evolved on both the chimp and gorilla lineages.
A quick glance at the two might give you the impression that chimps and gorillas are very much alike, but with more careful observation a lot of traits are actually quite different, and in many cases they do not share traits while we have another to any higher degree than one of those have a unique trait.
The time back to our shared ancestor with chimps is just as long for the chimp lineage as for the human lineage, so it makes sense that they have evolved just as much as we have, when you think about it. The time back to the gorilla is essentially the same, since the split with the gorilla and the split with the chimp are very close in time, so exactly the same argument goes there.
Traits that Ardipithecus share with humans include being omnivore — but then chimps eat fruit and gorillas eat leaves so you cannot really say that they share a trait that we do not here anyway — and more interestingly Ardipithecus might have been bipedal. To some extend, anyway, but not nearly as much as Lucy.
Now bipedalism is a trait that is usually strongly associated with humans, but even here the story is a bit more complex. The African apes are knuckle-walkers (the orangutan is not), but this trait might have evolved twice, so I don’t really have a problem with bipedalism being the ancestral trait and knuckle-walking being derived…
Anyway, whether this fossil is “shocking” or just interesting, it is certainly an important piece in the puzzle of our evolution.
The one thing that bothers me right now is the speciation time question. If Ardipithecus is 4.4 million years old and on the human lineage, how far back do we find the human-chimp speciation?
Our own estimate, based on genomic comparison, would actually put this speciation event more recent than that, at 4.1 mya, but this estimate is slightly biased and correcting for that we get up to about 4.4 mya.
Still too recent if Ardipithecus is well along the line leading to humans…