Literature

Most people interested in human evolution have learned that australopithecenes gave rise to Homo habilis which in turn gave rise to Homo erectus. Also, that Homo erectus is the ancestor to all the other Homo species including H. sapiens. This linear picture was undermined by recent finds east of Lake Turkana in Kenya. The research team discovered habilis and erectus fossils in the same rock formation. "The new fossils confirm the distinctiveness of H. habilis and H. erectus, independently of overall cranial size, and suggest that these two early taxa were living broadly sympatrically in the same lake basin for almost half a million years." This lengthy coexistence means that the species occupied distinct ecological niches. According to the lead author: "the easiest way to interpret these fossils is that there was an ancestral species that gave rise to both of them somewhere between two and three million years ago."
In a news report, Minkel writes: "The late evolutionary biologist Stephen Jay Gould used to rail against the notion of a ladder of perfection rising from early humanlike species to Neandertals to Homo sapiens at the pinnacle. Two new fossils unearthed near a lake in Kenya bear out Gould's preferred metaphor for human evolution - that of a bush with many branches." Whilst the new finds do undermine the popular "linear" view of human evolution, they are not necessarily support for a "bush with many branches" view. The latter results from the data being viewed with the premise that evolutionary transformation must have occurred and that apelike animals did turn into Homo sapiens. Without this premise, the data are not compelling.

Implications of new early Homo fossils from Ileret, east of Lake Turkana, Kenya
F. Spoor, M. G. Leakey, P. N. Gathogo, F. H. Brown, S. C. Anton, I. McDougall, C. Kiarie, F. K. Manthi and L. N. Leakey.
Nature 448, 688-691 (9 August 2007) | doi:10.1038/nature05986

Sites in eastern Africa have shed light on the emergence and early evolution of the genus Homo1, 2, 3, 4, 5, 6. The best known early hominin species, H. habilis and H. erectus, have often been interpreted as time-successive segments of a single anagenetic evolutionary lineage3, 7, 8, 9, 10. The case for this was strengthened by the discovery of small early Pleistocene hominin crania from Dmanisi in Georgia that apparently provide evidence of morphological continuity between the two taxa11, 12. Here we describe two new cranial fossils from the Koobi Fora Formation, east of Lake Turkana in Kenya, that have bearing on the relationship between species of early Homo. A partial maxilla assigned to H. habilis reliably demonstrates that this species survived until later than previously recognized, making an anagenetic relationship with H. erectus unlikely. The discovery of a particularly small calvaria of H. erectus indicates that this taxon overlapped in size with H. habilis, and may have shown marked sexual dimorphism. The new fossils confirm the distinctiveness of H. habilis and H. erectus, independently of overall cranial size, and suggest that these two early taxa were living broadly sympatrically in the same lake basin for almost half a million years.

See also:
Minkel, J.R. New Fossils Illustrate "Bushiness" of Human Evolution, Scientific American News, 8 August 2007

Luskin, C. Paleoanthropologists Disown Homo habilis from Our Direct Family Tree, Evolution News & Views, August 9, 2007