Friday, July 09, 2010
A Chinese Ape in Our Ancestry? Part 4
The overall phenetic similarity between the post-canine dentition of Lufengpithecus lufengensis and Ardipithecus ramidus is striking. This is particularly true given the fact that the two are separated by approximately two million years in time and thousands of miles in space. This is not the place to give a detailed morphometric analysis. It will suffice to illustrate the similarities with a few side to side visual comparisons. As is said a picture is worth a thousand words.
Of course we're dealing with rather nondescript typical Late Miocene thick-enameled hominoid teeth so the similarities are not all that startling. Nevertheless, they are real and pervasive. No wonder that when first described female specimens of Lufengpithecus were mistaken for early hominids (s.s.). The female canines are likewise very similar to homologues in Ardipithecus although the male canines are much larger, indicating a high degree of sexual dimorphism, at odds with what's seen in early hominids (s.s.). It seems to me that the only derived, defining character of hominids (s.s.) that stands the test of time is a significant decrease in the amount of canine sexual dimorphism from what is seen in other Late Miocene apes including Lufengpithecus. As this most likely denotes a profound change in species specific sexual reproductive strategies and socionomic relationships within the primate troop, a reduction in canine sexual dimorphism may be taken as the defining characteristic of hominids (s.s.).
To sum up, recent studies of Lufengpithecus show that it is most likely not a member of the orang clade, or if it is it must be nearly identical to the LCA of the modern great apes and humans. It is much too late in the fossil record to be that ancestor but it could be a relic species that epitomizes it. On the other hand, Lufengpithecus could be an early pre-hominid, phenetically close to the LCA of chimps and humans. Or, as many Chinese paleoanthropologists think Lufengpithecus was a bona fide hominid (s.s.). The latter supposition will be scoffed at by many in the West as just another example of Chinese hubris or wishful thinking. But why not? If Sahelanthropus at 7 mya is accepted as a hominid (s.s.) then the Hominidae must have diverged around the same time that Lufengpithecus hudienensis appears in the fossil record (~ 8 mya). For Lufengpithecus and Sahelanthropus to both be hominids would necessitate a quick dispersal of hominids from their center of origin immediately upon their origination. This is not so far-fetched as earlier and later cross continental hominoid dispersals are known in the fossil record. Where the poorly known Lufengpithecus keiyuanensiss dated to ~ 12 mya fits into all of this is currently unresolved. It is far too early to be a hominid (s.s.) so it may warrant a separate genus. No matter how its phylogenetic relationships are eventually resolved Lufengpithecus demonstrates that the basicranial and femoral traits previously thought to be diagnostic of the Hominidae (s.s.) may not be so. Either Lufengpithecus was a hominid (s.s.) or it demonstrates that the LCA of chimpanzees and humans, the African apes and humans, the modern great apes and humans, or some collateral branches thereof, shared in traits which have been thought to be diagnostic of erect bipedalism. With the recently published description of the Ardipithecus ramidus skeleton, combined with the greater clarity of the species defining traits of Lufengpithecus lufengensis, it now seems clear that bipedalsim may no longer be diagnostic of the Hominidae (s.s.). As with brain size, tool making, culture and any number of other defining traits that were once thought to make us "human" rather than "ape," bipedalism may fall by the wayside and no longer hold sway. The first direct humans ancestors had ape-sized brains, tool-making is commonly seen in the great apes and communal hunting and meat sharing occurs in chimpanzees. Cultural transmission is not unique to humans and now bipedalism may turn out to have been a trait that developed in our pre-hominid (s.s.) ancestors. What then makes us "human?" It may very well have been the development of social moieties that reduced direct male on male competition and regulated access to sexual reproduction.