Wednesday, February 22, 2012

What’s a man?

Studies of brain genetics are starting to reveal what makes humans human

THE problem with understanding human uniqueness is precisely that it is unique. Though the proper study of mankind may be man, that study will yield little if there is no reference point to compare man with.

That, at least, is the philosophy of Svante Paabo of the Max Planck Institute for Evolutionary Anthropology, in Leipzig. Dr Paabo, whose work on fossil DNA was the inspiration for “Jurassic Park”, has since become interested in human evolution. To this end, he and his colleagues have sequenced the DNA of both Neanderthal man and an Asian species of prehistoric human, the Denisovians, which Dr Paabo’s own work identified.

Now he has turned his attentions to modern Homo sapiens. In collaboration with a team from the Chinese Academy of Sciences, Dr Paabo and his colleague Philipp Khaitovich have compared genetic activity over the course of a lifetime in the brains of humans, chimpanzees and rhesus monkeys. They have then matched what they found with what is known of Neanderthals, and think they have thus discovered at least part of the genetic difference between Homo sapiens and the others that creates human uniqueness.

Dr Paabo and his colleagues focused their examination, just published in Genome Research, on two parts of the brain. One was the dorsolateral prefrontal cortex, which is the seat of abstract reasoning and social behaviour—things that humans are particularly good at. The other was the lateral cerebellar cortex, which is more to do with manual abilities. They extracted cells, post mortem, from people, chimps and monkeys of many ages, and looked at which genes had been active in these cells when the owners were alive.