A team of scientists led by anthropologist Tim D White of the University of California, Berkeley recently found 31 fossils of Australopithecus anamensis, our 4.1 million year old ancestor, while digging in Ethiopia's Middle Awash valley. The fossils, which come from at least 8 individuals, are anatomically similar to an earlier hominid, Ardipithecus ramidus, which lived 4.4 to 4.1 million years ago.

"There may have been times when one early hominid species evolved into another one without branching off into multiple species," White says. His view contrasts with that of researchers who suspect that hominids branched into many species over the past 6 million to 7 million years.

To prove that Au. anamensis branched from an earlier, as-yet-unknown population would require evidence that the Australopithecus species lived at the same time as Ar. ramidus, the Berkeley scientist notes. No such evidence exists.

The finding is interesting because Au. anamensis is early hominid species that evolved into Australopithecus afarensis, made famous by the discovery of Lucy. (Named because Beatles song 'Lucy in the Sky with Diamonds' was playing when they found her skeleton.)

Since Ar. ramidus and Au. anamensis lived in the same place and negotiated comparable habitats, it's plausible that the earlier hominid evolved directly into the later one, remarks anthropologist Alan C. Walker of Pennsylvania State University in University Park, a member of the team that found Au. anamensis fossils in Kenya.

From 4.2 million to 1.2 million years ago, Australopithecus evolved increasingly larger jaws and teeth from one species to the next with minimal or no evolutionary branching, Walker proposes.

Anatomical comparisons of earlier Au. anamensis and Au. afarensis finds, conducted by anthropologist Donald C. Johanson of Arizona State University in Tempe and his colleagues, also indicate that the older species evolved directly into Lucy's kind. Their study will appear in the Journal of Human Evolution.

Source: Science News