Author: Stephen Caesar
Subject: Early Man
Date: 11/09/2006

Research recently conducted by scientists at the Harvard Medical School, MIT, and the Broad Institute of Harvard and MIT has called into question some evolutionary theories regarding the origin of the human race. According to the Harvard Gazette, this research suggests “that ancestral humans split from chimpanzee forebears more recently than previously thought and raise the possibility that the two nascent species hybridized before making their final separation” (Powell 2006: 11).

The Gazette further reported that these “surprise findings” “also call into question the place on the primate family tree of fossils that scientists had thought were the bones of ancestral humans, but which are older than the newly determined time that the species diverged” (Ibid.).

David Reich, assistant professor of genetics at the Harvard Medical School, conducted the research in question. Also participating: Nick Patterson, Daniel Richter, and Sante Gnerre of the Broad Institute; and Eric Lander of MIT. The research was published in the May 17 2006 online edition of the journal Nature. They examined differences between the genomes of chimpanzees and humans, comparing the mutations in both to find out how long ago they shared a theoretical common ancestor (Ibid.).

For many years, evolutionary scientists have been stating that the theorized split between chimpanzees and humans into distinct species occurred between 7.4 million and 6.5 million years ago. The new research, however, claims that the split occurred “about a million years later than the previously accepted range…” (Ibid.). Moreover, the new findings suggest that, as the two budding species theoretically split, members of each species may have interbred to form hybrid offspring:

“Under the hybridization scenario, the ancestors of humans and chimpanzees split from their common ancestor. After that initial separation, however, members of the two new species interbred an unknown number of times. Fertile hybrid offspring then may have mated back into one or both original populations, bringing in genes from the other species and leaving traces in the genetic code” (Ibid. 11-12).

According to Eric Lander, the director of the Broad Institute, “The genome analysis revealed big surprises, with major implications for human evolution” (Ibid. 12). However, as with so many theories regarding human origins, this latest finding is not set in stone, according to the Gazette: “Reich cautioned that though hybridization would answer several questions raised by the research, the research itself does not prove that hybridization occurred” (Ibid. 11). Nonetheless, Reich indicated that (in the Gazette’s words), “the findings may cause scientists to re-examine beliefs about speciation and the role of hybridization. Current thinking is that although hybrids do occasionally occur in nature, they are sterile or less fit than the parent populations and so eventually die out” (Ibid. 12).

Regardless of whether the hybridization theory holds true, the team’s findings have called into question “several prominent fossils” that have been touted as modern humans’ evolutionary ancestors (Ibid.). Premier among them is the Toumai fossil, Sahelanthropustchadensis. Scientists have dated this fossil to between 7.4 and 6.5 million years ago. In recent years it has been held up as one of the earliest direct evolutionary ancestors of mankind. However, as the Gazette reported, Toumai may soon be dethroned: “Though it [the Toumai fossil] has humanlike features, the fact that it predates the time when human ancestors finally split from chimpanzee ancestors throws its place on the human family tree into doubt….” (Ibid.).

Regardless of whether the new theory posited by Reich and his colleagues proves true in the end, the team’s findings do demonstrate the highly cloudy nature of the search for human origins. It is inadvisable for one group of paleoanthropologists to laud their findings as the last word in human evolution, since it is highly likely that, sooner or later, a new group of scientists will make a discovery or come up with a theory that wipes earlier theories off the map.

 

Reference:

Powell, A. 2006. “Findings cloud human, chimp origins.” Harvard Gazette. 18 May.

 

Stephen Caesar holds his master’s degree in anthropology/archaeology from Harvard. He is a staff member at Associates for Biblical Research and the author of the e-book The Bible Encounters Modern Science, available at biblepm@hotmail.com.