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The journal Science* has a special collection of articles on a new Australopithicene species out. This is the disocvery of Australopithecus sediba led by Lee Berger and his team at the Malapa site in South Africa.

As excited media get hold of these discoveries, a few points should be recognised.

First, this isn't the missing-link between chimps and humans. Technically, because there is no such thing as a missing-link. These are imaginary constructs employed by 50's Horror Movie directors and creationist. The term 'missing-link' should be purged form any reputable news report.

It is however an important transition-fossil. That means it has features we anticipate our human ancestors should have, in geological stratas we expect them to appear. The transition from Australopithicene species to Homo species, is widely accepted. This new fossil species adds to the transitionary picture.

Second, the fossil is unnecessary to demonstrate human evolution from a common-ape ancestor. Biology has long since amassed an array of data that ranges from anatomical, through to molecular and DNA based, that evidence our evolution. This fossil isn't some vital piece of the puzzle. Things like the human appendix, the convergence of alpha-hemoglobin chains between related ape-species and humans, the commonality of genetic mistakes like the GULO pseudogene (that's why we and other apes can get scurvy), or common ERVs, have long since demonstrated our evolution.

So what is the significance of this new species? Well, it is a younger fossil (about 2m years) than Lucy (about 3.2m years). So it appears at a point that is much closer to the actual Australopithicene-Homo transition. It provides more details on the order and form of the transition. These lie in the areas of the skull, the hands and feet and the pelvis. These all show a shift from the older Australopithicene fossils to traits shared with Homo. And this leads Berger and his team to propose that this is the most probable direct ancestor for humans.


www.sciencemag.org SCIENCE VOL 333 9 SEPTEMBER 2011