Notice anything dubious about this screen-capture of the Discovery Channel's "Ardi" page? Ardi's eyes have white sclera. What is the evidence for that? Primate eyes tend to have black sclera. Having whites of eyes is a peculiar human trait, one that means we make redirecting attention easy. Could Ardi do that? I've seen no reason to think so. (Check out this webpage here.)
A team of scientists have announced in a special issue of Science magazine new details resulting from the extensive study of a series of Ardipthecus ramidus fossils from 4.4 million years ago. The centerpiece of the new report concerns a skeleton of a female the team has nicknamed "Ardi." Although not complete, the skeleton includes the skull, teeth, arms, hands, pelvis, legs, and feet. All in all, it makes for a bad day to be defending creationism. The project's co-director, Tim White, said, "It's not a chimp. It's not a human. It shows us what we used to be."
Ardipithecus lived long before speech in any form is suspected to have evolved, but the report does have implications for language-origin theory. In particular, Ardipithecus seems to have had a completely unexpected social arrangement. Ardi is estimated to have weighed about 110 pounds (50 kg), making her more or less equal in size to her male conspecifics. The difference in sizes for the diferent sexes that is found in chimpanzees and especially gorillas does not appear to have been found in ramidus. Sexual dimorphism (as sex-based size differences are called) commonly reflect strong competition among males for sexual access to females. A lack of dimorphism suggests a lack of competition. This finding raises new questions for Terrence Deacon and his theory that symbolism developed in response to a need to limit competition between males over females. If the competition disappeared two million years before the first Homo, it is hard to credit Deacon's account of language origins.
I asked Deacon for a comment and he replied:
My argument is NOT that low sexual dimorphism is a correlate of symbol use, in general, it is only a correlate of minimal male-male competition. So my argument is only that that a *reduction* in sexual dimorphism from our more immediate ancestors the australopithecines (which we can now assume must have increased in sexual dimorphism since ardipithecines) indicated a reduction in overt male-male competition (over compulatory access). The ardi data is in this respect no more relevant than the gibbon data.The press kit had an astonishing speculative account of behavior:
Ardipithecus probably had a social structure unlike that of any living primate—one in which multiple males and multiple females lived together, but without strong male-male conflicts. Males were probably pair-bonded to specific females, and may have aided females by gathering rare and valuable foods that they would regularly share with them.
Among the other surprising findings:
- The species is not much like a chimpanzee, suggesting that chimpanzees and bonobos have evolved quite considerably since the last common ancestor with humans. We can no longer assume the last common ancestor was much like a chimpanzee in behavior or anatomy.
- Although Ardipithecus was bipedal, it was as well adapted to climbing trees as to walking on the ground.
- Its foot retained the grasping toe of a chimpanzee, indicating that it did not have the arched foot of an Australopithecus.
- The face was neither flat and massive as the later Australopithecus, nor projecting like a modern ape.
- The hand shows no signs of specialization for knuckle walking (like chimps and gorillas) and no signs of having evolved from a hand that ever knuckled walked. This detail indicates that the knuckle walking of chimpanzees and gorillas evolved twice along separate, convergent lines.
- The brain was about 300-350 cc, just slightly smaller than a modern chimpanzee.