Post details: Human evolution data can be likened to a pointillist painting

09/23/07

Permalinkby 06:52:37 am, Categories: Literature - Articles, 626 words   English (UK)

Human evolution data can be likened to a pointillist painting

Homo erectus bones from Dmanisi, Georgia, have been identified as the "earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia." Differences between them and other representatives of H. erectus have been carefully scrutinised. Some have commented that the differences suggest the Dmanisi bones are transitional between habilis and erectus, but others emphase the highly variable nature of early erectus fossil material.
In a News & Views essay, Daniel Lieberman wrote: "When viewed close up, however, the Australopithecus-Homo transition has always been murky. One problem is that we don't know enough about Homo habilis, the putative ancestor of H. erectus."
Also, "In some respects, H. habilis looks like a good candidate as the ancestor of H. erectus; it has a vertical face, teeth of intermediate size between those of australopithecus and H. erectus, and an intermediate sized brain. But the oldest fossils definitively attributed to H. habilis are 1.9 million years old and thus no older than the oldest H. erectus fossils. Moreover, Spoor et al also report a new H. habilis upper jaw dated to 1.44 million years ago, extending the species' temporal overlap with H. erectus. (For more on Spoor et al., go here).
Lieberman introduced his essay with these words: "The fossil record of human evolution is like a pointillist painting: one sees a different picture close up from when one stands back." This analogy is actually very helpful. Normally, in science, gaining more data helps to fill in the picture so that the details can be seen more clearly. However, this is not so in human evolution. Gaining more data frequently leads to headlines that suggest a radical rethink of previous "knowledge". In this case, we have more data implying a mosaic of characters and greater variability. Zooming in on the picture is not revealing the details of a transformation story. Like a pointillist painting, evolution is only apparent from a distant vantage point. Close up, we see masses of data, but no coherent picture. In situations like this, it is particularly important not to impose theory (of evolutionary transformation) on the data.

Postcranial evidence from early Homo from Dmanisi, Georgia
David Lordkipanidze, Tea Jashashvili, Abesalom Vekua, Marcia S. Ponce de Leon, Christoph P. E. Zollikofer, G. Philip Rightmire, Herman Pontzer, Reid Ferring, Oriol Oms, Martha Tappen, Maia Bukhsianidze, Jordi Agusti, Ralf Kahlke, Gocha Kiladze, Bienvenido Martinez-Navarro, Alexander Mouskhelishvili, Medea Nioradze & Lorenzo Rook.
Nature, 449, 305-310 (20 September 2007) | doi:10.1038/nature06134

Abstract: The Plio-Pleistocene site of Dmanisi, Georgia, has yielded a rich fossil and archaeological record documenting an early presence of the genus Homo outside Africa. Although the craniomandibular morphology of early Homo is well known as a result of finds from Dmanisi and African localities, data about its postcranial morphology are still relatively scarce. Here we describe newly excavated postcranial material from Dmanisi comprising a partial skeleton of an adolescent individual, associated with skull D2700/D2735, and the remains from three adult individuals. This material shows that the postcranial anatomy of the Dmanisi hominins has a surprising mosaic of primitive and derived features. The primitive features include a small body size, a low encephalization quotient and absence of humeral torsion; the derived features include modern-human-like body proportions and lower limb morphology indicative of the capability for long-distance travel. Thus, the earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia did not yet display the full set of derived skeletal features.

See also:

Dalton, R., Treasure trove of Homo erectus found, news@nature.com: 19 September 2007; | doi:10.1038/news070917-6

Lieberman, D.E., Homing in on early Homo, Nature, 449, 291 - 292 (20 September 2007) | doi:10.1038/449291a

Luskin, C. Human Origins Update: Harvard Scientist and New York Times Reporter Get the "Plug Evolution Memo"...Sort of
Evolution News & Views, September 22, 2007

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