Sunday, December 5, 2010

Life Lines 67


At the 74th annual symposium held at Cold Spring Harbor Laboratory, Svante Pääbo presented a paper on the Neandertal genome. Pääbo is a pioneer in extracting ancient DNA and sequencing it. The Neandertals were a species that lived about 400,000 to 30,000 years ago when they went extinct. Pääbo used 75 bones from specimens found in Europe and the Middle East and found that only the more recent bones (30,000 to 40,000 years old) had enough DNA in them to amplify and give fragments large enough to sequence. The average size of the fragments he used was about 50 nucleotide pairs in length. By then matching these through computerized matching, he was able to show that they were similar to our own Homo sapiens sequences from our completed genome. That match-up also showed he had covered 60 percent of the Neandertal genome. He hopes to have a nearly complete genome as he analyzes additional Neandertal bones.

There are lots of problems doing this kind of analysis. Of the DNA he extracts only 3.5% is primate DNA. The rest is bacterial or fungal. The Neandertal genes differ from Homo sapiens genes by about 12.8% so there have been many mutations taking place over the time these two species split off from a common ancestor about 500,000 years ago. One major difference between humans and Neandertals is that Neandertals did not have a symbolic culture (paintings, engravings, sculptings) in their artifacts. Many anthropologists have surmised they lacked the capacity for a spoken language. There is a gene known as FOXP2 which is essential for human vocalization and mutations in that gene lead to mute or inarticulate speaking. The Neandertal DNA does have FOXP2 but it differs in two of its nucleotides and may have been mute.

Pääbo has synthesized the gene and put the human FOXP2 gene into mice. It changes their activities (more cautious movements), increases cell number in the corpus striatum, leads to more synaptic unions, and diminishes dopamine in the brains of the mice. As Pääbo looks for uniquely human genes he hopes to test these in mice to see how they affect mouse physiology or behavior. He believes this approach over the coming years will teach us how humans differ from other primates as well as from our nearest extinct ancestor, the Neandertals.

Stephen Pinker who also spoke at this symposium suggested that humans might differ from other primates by possessing a “cognitive niche” which allows them to use cause and effect reasoning. This process allows the permutation of several words and ideas into immense combinations and gives humans an edge when facing novel situations. For the rest of the animal kingdom there is a much slower response (often natural selection leading to the loss of many and the survival of a few). If Pinker is correct and this is why humans are so much smarter than other animals, the genes associated with cause-effect reasoning will be among the most likely candidates that define our uniqueness. Language is beneficial to our species because it is given at little cost. As Pinker described it “when you give someone a fish you have surrendered something you had, but when you tell someone how to fish, you do not lose a fish and you do not lose the idea of how to fish.” I would add, you might even get some fish in return out of gratitude.

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