“We Are All Humans” – Pat Shipman – [Co-Author “Erik Trinkaus and Pat Shipman, The Neandertals:  Changing the Image of Mankind (Alfred A. Knopf:  New York), 1991]

Homo sapiens sapiens

American Scientist, November-December 2003 Volume 91, Number 6, Marginalia, “We Are All Africans, by Pat Shipman, page 496 DOI:10.1511/2003.6.496

                                                QUOTE:  I don’t expect that the subscribers of the Multiregional hypothesis will be waving a white flag of surrender, although they have lost the great majority of their supporters. At least one of the theory’s most ardent proponents, Wolpoff, is still steadfast in defense of the hypothesis he has so long espoused. While it remains possible that new findings will shift the balance in favor of the Multiregional viewpoint, the consilience of such evidence creates a powerful testament. It would take many new fossils and many new genetic studies to resculpt this intellectual landscape.

“New theories are, sadly, easier to come by than new primary evidence.  Thus it is a joyous occasion when my paleoanthropologist colleagues appear to resolve one of the most bitterly debated questions in the discipline: the issue of when, where and how modern humans evolved.  For decades, paleoanthropologists have argued over two competing theories about the origin of our kind. The older notion, which owes its crude beginnings to Charles Darwin, is the Out of Africa hypothesis. This theory maintains that modern humans evolved in Africa and then spread around the worldBoiled down to its essence, the hypothesis states that modern humans are both relatively recent (100,000 to 200,000 years old) and African in origin.

The rival Multiregional hypothesis argues that modern humans evolved in many locations around the world from a precursor species, Homo erectus, approximately one to two million years ago.   The Multiregional hypothesis predicts that the fossilized remains of the earliest modern humans will be found all over the Old World and that these scattered fossils will all date from about the same timeUnfortunately for adherents of the Multiregional hypothesis, recent results are weighing heavily against them. Three very different strains of evidence have converged to offer convincing support for the rival theory.

(1) Genetic Diversity:  Tishkoff and her colleagues chose to investigate East African peoples for specific reasons. The number of linguistic and cultural differences is unusually high in the region, as is the variation in physical appearance—East Africans are tall or short, darker-skinned or lighter-skinned, round-faced or narrow-faced, and so on. This observation suggested that the genetic composition of the population is highly diverse, and as expected, the team found substantial variation in the mtDNA. In fact, members of five of the lineages showed an exceptionally high number of mutations compared with other populations, indicating that these East African lineages are of great antiquity.

The efforts of the University of Maryland group reflect a substantially larger database and more certain geographic origins for its subjects than earlier mtDNA studies.

Further, the work by Tishkoff’s team reveals that these five East African populations have even older origins than the !Kung San of southern Africa, who previously had the oldest known mtDNA.  These samples showed really deep, old lineages with lots of genetic diversity,” Tishkoff says. “They are the oldest lineages identified to date. And that fact makes it highly likely that ‘Eve’ was an East or Northeast African.

My guess is that the region of Ethiopia or the Sudan is where modern humans originated.

By assuming that mtDNA mutates at a constant rate, Tishkoff’s team estimated that the oldest lineages in their study originated 170,000 years ago, although she cautions that the method only gives an approximate date. Nonetheless, this finding is neatly congruent with new fossil evidence.

(2) This past June, an international team headed by Tim White and F. Clark Howell of the University of California at Berkeley, and Berhane Asfaw of the Rift Valley Research Service in Addis Ababa announced the discovery of three fossilized human skulls in the Herto Bouri area of Ethiopia. Volcanic layers immediately above and below the layer were dated to 154,000 and 160,000 years using radioisotopes, meaning that the owners of the skulls lived sometime between those dates.

Although the African Herto skulls are longer and more robust than those of recent humans, the team considers the Herto specimens to be the earliest modern Homo sapiens yet found—direct ancestors of people living today. In an unknowing echo of Tishkoff’s genetic findings, Tim White concludes, “We are all, in this sense, Africans.”

Because the discoverers of the Herto skulls were unable to find convincing links between these fossils and archaic humans from any single geographic region, they put the three specimens into a new subspecies, Homo sapiens idaltu. The subspecies name idaltu comes from the Afar language of Ethiopia. It means “elder.”

Even paleoanthropologists who were not associated with the finds overwhelmingly agree that the Herto skulls are the earliest securely dated modern humans yet found, meshing with the Out of Africa hypothesis.  The Herto fossils also fit neatly into an African succession: Older skulls from the region include Homo erectus fossils from Daka, dated to about 1 million years ago, and the archaic Bodo skull, estimated to be about 500,000 years old.

Meanwhile, fossils from Omo Kibish, also in Ethiopia, are more recent than the Herto skulls, according to a reanalysis of those remains. For a long time, the Omo Kibish specimens were regarded as ambiguous: They were fragmentary, making their anatomy less clear, and the site was originally dated using older, less reliable methods.  However, a recent relocation of the site turned up new pieces that glued onto specimens found in 1967, and the site was re-dated to about 125,000 years using modern techniques. Further evidence comes from the Qafzeh site in Israel—on a plausible route from Africa—where there is a 92,000-year-old modern human skull.

These findings establish the earliest modern humans in Africa, but they do not exclude the simultaneous evolution of modern man in other parts of the world, as suggested by the Multiregional hypothesis. The most pertinent test of Multiregionalism focuses on Neandertals, which are a uniquely European form of primitive humans. According to Multiregionalists, Neandertals (which lived between about 200,000 and 27,000 years ago) are a transitional form that connects European Homo erectus to modern Homo sapiens sapiens. Could the Herto skulls simply be the regional, African equivalent of Neandertals?

“No,” says co-leader Berhane Asfaw definitively. “The Herto skulls show that people in Africa had already developed the anatomy of modern humans   Asfaw states, “We can conclusively say that Neandertals had nothing to do with modern humans based on these skulls and on the genetic evidence.”

[Berhane Asfaw is an Ethiopian paleontologist of Rift Valley Research Service, who co-discovered human skeletal remains at Herto Bouri, Ethiopia that revealed a transition into modern humans (homo sapiens sapiens).  The specimen was called homo sapiens idaltu (elder).]

The genetic evidence to which he refers has accumulated over the last six years, but the most dramatic advance came in 1999, when a team led by Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, became the first to extract mtDNA from the original Neandertal specimen. His group’s success was a spectacular tour de force of meticulous technique and solid research design. The ancient mtDNA was compared with mtDNA from more than 2,000 people living in various regions around the world and differed from each of the modern regional groups by an average of 27 mutations (out of a possible 379 that were examined). Contrary to the predictions of the Multiregional hypothesis, the mtDNA of Neandertals was not closer to that of the modern Europeans.   The work was a strong blow to the theory that humans evolved in several places simultaneously.

Multiregionalists Milford Wolpoff of the University of Michigan and Alan Thorne, then of Australian National University in Canberra, challenged the conclusions. They urged an investigation of mtDNA from additional Neandertals, in case the single individual used by Paabo’s team was particularly unusual.  They also suggested that Neandertal mtDNA might be closer to samples from the fossilized remains of early modern humans in Europe than from living Europeans.

Since these criticisms were levied, several teams have carried out additional studies of mtDNA from Neandertals and fossilized modern humans.  All have shown that Neandertal samples differ significantly from modern mtDNA, which is indistinguishable from fossilized modern human mtDNA. Giorgio Bertorelle of the University of Ferrara in Italy led one of these teams, which published important results last May.

Bertorelle’s team compared mtDNA from two early modern humans (Cro-Magnons) from Italy, dated to 23,000 and 24,720 years old, with four mtDNA sequences of Neandertals from 42,000 to 29,000 years ago. The chronological proximity of the Neandertal and modern fossils was key because it increased the likelihood that Neandertal mtDNA would strongly resemble the early modern human mtDNA—if the former evolved into the latter, as the Multiregional hypothesis states.

Bertorelle and colleagues found that the Cro-Magnon mtDNA was unlike the Neandertal samples, differing from them at 22 and 28 sites out of 360. Instead, the Cro-Magnon mtDNA sequences fell squarely within the range of variation of living humans.  One of the Italian Cro-Magnons had a sequence shared by 359 (14 percent) of 2,566 modern samples in Europe and the Near East, and the other differs by only one mutation.  The early modern humans had sequences that living individuals still have,” concluded Bertorelle, they [have] … nothing to do with Neandertal sequences.” He and Asfaw might chime in unison that Neandertals cannot represent a regional European transition from Homo erectus to modern Homo sapiens.

The identity between Cro-Magnon and modern human mtDNA sequences in this study and others is striking, and it has caused some researchers to worry about the possibility of mtDNA contamination from researchers or others who have handled the fossils. Although contamination is a major problem in such studies, Bertorelle asserts spiritedly that his data are clean, stating that his group performed nine different tests to check for contamination and followed the most stringent procedures and methodology. He also points out the irony of questioning the validity of the mtDNA of a prehistoric human only because it is identical to that of modern humans.

The Out of Africa hypothesis has become compelling because these different studies have all yielded congruent answers. Tishkoff’s work points to East Africa in general, and Ethiopia/Sudan in particular, as the region where the oldest modern human lineages are found—and probably evolved. Studies of ancient mtDNA by groups led by Paabo, Bertorelle and others emphasize the genetic discrepancies between Neandertals and modern humans and demonstrate that some early anatomically modern fossils were also genetically modern—undermining the Multiregional hypothesis.

Despite the power of these genetic studies, only the fossils can tell us what our ancestors actually looked like, what they actually did and where they actually lived.  It is singularly satisfying that the White-Howell-Asfaw team has discovered fossilized human remains from the right place (Ethiopia) and time (about 160,000 years ago) that also have the right (modern human) anatomy. The authors of the Out of Africa hypothesis are celebrating.

I don’t expect that the subscribers of the Multiregional hypothesis will be waving a white flag of surrender, although they have lost the great majority of their supporters. At least one of the theory’s most ardent proponents, Wolpoff, is still steadfast in defense of the hypothesis he has so long espoused. While it remains possible that new findings will shift the balance in favor of the Multiregional viewpoint, the consilience of such evidence creates a powerful testament. It would take many new fossils and many new genetic studies to resculpt this intellectual landscape.

© Pat Shipman


About Harold L Carter

Bachelor of Science, Columbia University Masters degree, Ohio State University Undergraduate National Officer, Alpha Phi Alpha Fraternity, Eastern Asst Vice President, when a student at Columbia University Profile Photograph: Mom & Me, when I was a graduate student
This entry was posted in Uncategorized and tagged . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s