Frontier - In brief

A Homo floresiensis skull (left) compared with a modern-day human skull. © Peter Brown
A Homo floresiensis skull (left) compared with a modern-day human skull. © Peter Brown
Reconstitution of the Neanderthal child of Gibraltar (Anthropological Institute, University of Zurich).
Reconstitution of the Neanderthal child of Gibraltar (Anthropological Institute, University of Zurich).

The Flores enigma

Led by Peter Brown, in 2003 a team of Australian and Indonesian researchers discovered the skeleton of an unknown, small (less than one metre long) species on the Island of Flores (Indonesia). Baptised Homo floresiensis, Brown's discovery created a stir around the world. Fossils of several other similar individuals were later found in a cave. Around 18 000 years old, they pose a number of questions. Does this species derive from Homo erectus, who is believed to have colonised the world, or does it derive from Homo habilis, whom it more closely resembles? In this case, how is it that no remains of the latter have ever been found outside Africa? Homo floresiensis, which seems to have disappeared about 12 000 years ago, was in any event a contemporary of Homo sapiens during tens of thousands of years. Without doubt its insularity preserved it from the expansionism of our species.

Neanderthal reveals all

Neanderthal Man, discovered in 1856, poses a number of enigmas. We know that he lived in Europe and in western Asia about 400 000 years ago and that he disappeared 28 000 years ago, with Homo sapiens then becoming the sole representative of human primates. Why did he become extinct? What do these two species have in common? Genetics is just starting to lift the veil. In 2006, two groups of researchers, one American (led by Edward Rubin) and one European (led by Svante Pääbo at the Max Planck Institute in Leipzig) carried out a partial sequencing of Neanderthals' nuclear DNA.

"It is quite extraordinary that we can obtain the genome of an extinct species," says Jean-Jacques Hublin, director of the Human Evolution Department at the Max Planck Institute. "Until now we were studying mitochondrial DNA, which allows us to construct phylogenetic trees, but which does not provide any information on the specific features of individuals in the way that nuclear DNA allows. This latter DNA is particularly complex, with 3 billion base pairs (compared with 16 000 in mitochondrial DNA). The Leipzig team has sequenced almost 60% (2 billion base pairs), and is determined to finish the job. "Today we can compare the genomes of man and chimpanzees, our closest relative. The differences are minimal. But these two species separated 6 or 7 million years ago. What we don't know is when the genetic features specific to Homo sapiens appeared. Was it 100 000 or was it 6 million years ago? The decrypting of the Neanderthal genome could provide part of the answer."

We already know that the FOXP2 gene, which plays a role in the production of language, is identical in Neanderthal and in modern man, and that Neanderthal Man had reddish hair - but that the gene responsible for this was structured differently to the gene responsible for red hair in modernday European populations. "This character of the genotype must therefore have appeared at least twice, in separate lines and with different gene structures, probably for identical reasons of adapting to the environment." Further study of Neanderthal Man's nuclear DNA should make it possible to determine other elements, like the size of the population and whether or not any cross-breeding occurred with Homo sapiens.

Apes: genes and cognition

How do we track down the genes that are potentially involved in cognition in humans? Ralf Sudbrak of the Max Planck Institute of Molecular Genetics in Berlin (DE) has listed three categories of these genes, each corresponding to a form of apparition in the course of evolution. The first are genes that have taken on new functions following remodelling of primates' genes; the second are genes that present an accelerated evolution in human beings (detectable by comparing their mutation rates with those of homologous primate genes); the third are genes homologous to those identified in mice for their role in the differences in cognitive performance between different families of rodents. It is these three properties that Sudbrak - previously involved in analysing the sequences of chimpanzee chromosome 22 and human chromosomes X and 3 - is proposing to go looking for in the genomes of human and non-human primates as part of the Apes consortium. Once these candidate genes have been identified by comparative analysis of their sequences, it remains to study their detailed structure, more specifically that of the promoters control gene expression, and of course, the biological function.

The Apes project is part of the European initiative Nest Pathfinder, What it means to be human.

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