The phylogeny of Hominini is definitely the most important and interesting part of the Anthropological Halls in most of the natural history museums. Many visitors will stop in front of the fossils of
Australopithecus and learn what our ancestors might look like. By this time, people will seldom question that
Australopithecus was an ancestor of human, just like Chinese people used to trace their ancestry to Peking man for granted decades ago. However, sufficient genetic studies invalidated that preconception subsequently. Therefore, we may rethink that why
Australopithecus must be the direct ancestors of human. Are there sufficient evidences? Or is there another possible that
Australopithecus was just on a side branch away from the evolutionary trunk of human? In a way, to take
Australopithecus as our ancestor for granted may result from the opinion of the single-line anagenesis, while there are few cases in the nature.
When looking into the present version of the Hominini phylogeny (A), we find that there is an obvious trend to put most of the fossil genera on the main stem evolving to human. Besides
Orrorin and
Australopithecus,
Adipithecus was also thought to be on the main stem by most of the paleoanthropologists, although it was distinctly similar to chimpanzees rather than to human. In the same mode of thinking,
Kenyanthropus and
Paranthropus were put on short side branches affiliated closely to the main stem, which made the evolutionary history of human quite ample. On another side, people always complain that the ancestor of chimpanzees was yet missing. The genus Pan seems to have appeared suddenly. This kind of imbalance can most likely be attributed to the misunderstanding of the fossil genera, such as regarding
Adipithecus as human ancestor.
. The present Hominini phylogeny (A) and a possible reconstruction (B).
The most robust phylogeny is that constructed with the genomic data, however, there were no DNA remained in any fossils older than one million years. Therefore, the Hominini phylogeny was not based on genomes but phenomes. Unfortunately, fossils of the Hominini genera are mostly incomplete or even fragmentary. That means not many phenotypes can be extracted from the fossils and there are still nondeterminacies for the divergences. One of the phenotypes, angle of femur neck which is related strongly to bipedalism, exhibits a strange atavism along the present phylogeny. The angle of
Orrorin was much larger than that of
Australopithecus, which indicates
Australopithecus might not be as good at bipedalism as the
Orrorin was. Then, why was Lucy our grand grandma while she died from fall out of tall tree [
1]?
More weird phenotypes of
Australopithecus were pointed out in a letter [
2] sent to Nature Anthropology recently. The most interesting phenotypes showing the contradiction are the skull feature and footprint. Both of the phenotypes of
Australopithecus were more similar to Pan or even to Gorilla than to human. Although there was no statistical analysis, the suggestion of this letter, a possible reconstruction of the Hominini phylogeny to move
Australopithecus to the branch of chimpanzee, is worth while and thoughtful (B).
Besides the merits, some points of this letter may be excessive. For example, the authors suggested to put Gorilla onto the branch of
Australopithecus and
Pan, while that is inconsistent with the genomic phylogeny of the three existing species. The divergence time between human and
Pan is seven million years, while that between human-
Pan and
Gorilla is ten million years [
3,
4]. If both
Pan and
Gorilla were evolved from Australopithecus, the divergence time will have to reduce by half. As a scientific consensus, we believe more in genomic phylogeny than in physical phylogeny. We have to consider other possible reasons caused the similarity between
Australopithecus and
Gorilla.
Nature Anthropology is a highly integrated journal and we are open to receive all submissions on anthropological research, including opposing views that may spark some arguments. We encourage a broader body of academics to carry out conversations so as to cross-fertilize critical debates among anthropologists. Open discussion is always good for science.
