Redefining Human

From Oxford University Press Blog, regarding Aaron Filler's recent, very controversial, and very interesting publications.

It's easy enough for anyone to tell the difference between a human and an ape today, but how easy would it have been six million years ago, around the time of the split between the lineage of modern humans and the lineage of the chimpanzees. If you were to see the common ancestor would you think "human" or would you think "ape?"

Over the past 50 years there has been an understanding in the scientific community that the common ancestor would look somewhat like a knuckle-walking chimpanzee and that the various descendant lineages on the human side would more or less gradually begin to stand upright and walk bipedally on two legs. The common ancestor was a lowly quadrupedal ape, but our direct predecessors then gloriously stood upright on their two legs and eventually strode their way across the border between animality and humanity.

For many years, there was no solid fossil evidence to support this understanding. Now we have dozens of relevant fossils but they all seem to show that this scenario is wrong. In fact, the common ancestor may well have looked much more like a human than like an ape.

This sharpens the question, - is there a quintessential aspect of an animal that makes it a human? Can this be identified on a discreet biological basis so that the relevant critical gene changes can be spotted by genome researchers?

The piece is quite long and has lots of pretty pictures. Enjoy!