Tuesday, August 12, 2008

Neanderthal jigsaw puzzles

In August 1856, more than three years before Darwin published The Origin of Species, the top of a skull and fifteen other bones were recovered from a cave (the Kleine Feldhof grotto) in the Neander valley near Düsseldorf in Germany. A local teacher Johann Carl Fuhlrott soon identified them as human, and along with local anatomy professor Hermann Schaaffhausen, described the bones in a paper in 1857, suggesting that they represented the remains of an ancient extinct race of humans. Now known as Neanderthal 1, Fuhlrott’s fossil bones became the type specimen for a new species, Homo neanderthalensis (although in retrospect earlier finds from Belgium and Gibraltar belong to the same species).

In 1997, pioneering Swedish molecular archaeologist Svante Pääbo (b. 1955) obtained the first mitochondrial DNA sequence from the original Neanderthal specimen and confirmed that Neanderthals lay outside the range of variation seen in modern humans. Less than two years ago, Neanderthal genetics was transformed into stone-age genomics, when powerful new sequencing approaches were applied to a 38,000-year old leg bone from the Vindija cave in Croatia. Two papers appeared in November 2006 revealing analyses of up to a million base pairs of Neanderthal genome sequence. More recent analyses have established that the Neanderthal FOXP2 gene (potentially involved in speech) was identical to that in modern humans, that at least some Neanderthals had pale skin and red hair, but that Neanderthal Y chromosomes differed from those of modern humans. 

This week Pääbo and his team have delivered the next breakthrough in Neanderthal genomics with the publication in the journal Cell of the complete sequence (35-fold coverage) of a mitochondrial genome from the Vindija Neanderthal sample. The newly assembled sequence has allowed Pääbo’s team to estimate how much contamination from modern human DNA has affected their analyses (very little), how DNA gets degraded with time and to evaluate the prospects for a full nuclear Neanderthal genome (good). For a fuller discussion, see the posting by John Hawks in his own blog.

Although assembly of this molecular mitochondrial jigsaw is a remarkable achievement, for me the most jaw-dropping moment in recent studies on Neanderthals comes from the solution of a more tangible puzzle. The cave where Neanderthal 1 was discovered was destroyed in the 19th century, as the area was excavated and flattened to provide the local steel industry with limestone. It was thus generally assumed that the first, and most important, Neanderthal site was lost to science. But in the late 1990s, German archaeologists Ralf Schmitz and Jurgen Thissenset set about finding it. Poring over 19th-century paintings and old maps, they recognized a rock that still stood in the valley. They dug nearby and found cave debris. After careful examination, a team of archaeologists found over sixty Neanderthal skeletal fragments, from at least three individuals. Their efforts culminated in a triumphant solution to a skeletal jigsaw puzzle: three of the newfound bony fragments fitted perfectly on to the original specimen, excavated near a century and a half before (read more here)!

Oh and one final point! Palaeoanthropologists (or should that be “paleoathropologists”) cannot decide on how Neanderthal should be spelt. All agree that the original spelling Neanderthal is preserved forever in the species name Homo neanderthalensis, but in recent years a number of them, including Pääbo, have taking to using the modern German spelling for the Neander valley (Neandertal) to describe members of this species. In PubMed, at the time of writing, “Neanderthal” beats “Neandertal” by 209 to 183 citations. Someone somewhere should make a definitive ruling on this!

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