What Separates Us from the Apes? Neandertals and the Path to the Modern Human

The complexity of genetic changes which gave rise to humans as we exist today means that we cannot deduce much from the study of only single genes, but need rather to compare the whole genomes of closely related organisms. He described a study of the variation between modern human and Neandertal genomes and argues that combined with clues about which traits distinguish us most from our closest evolutionary neighbours, such studies can help us to unravel key influences in our evolution, that may in turn shed light on problems in the modern world.

A great challenge for researchers is to better understand the genetic and evolutionary background of the phenotypic traits that set humans apart from other species, and especially from our closest evolutionary relatives, the great apes. While paleontology and archaeology focus on fossils, human, and cultural remains, the approach ofcomparative genomics has been used to examine the genetic makeup of modern humans, our close relatives, the great apes, and at ancient DNA. This work has shown that humans and chimpanzees, share a common ancestor estimated to have been around some 4 to 7 million years ago. Analysis of human and ape DNA from different individuals show that the great ape populations are quite genetically diverse, whereas all humans are very similar at the genetic level. If we consider that the current human population is estimated at 6.5 billion, while the chimpanzee and gorilla populations number only in the few hundreds of thousands, this difference is highly significant and almost certainly reflects the capacity of human groups to migrate and intermix despite cultural boundaries. In fact, further clues regarding the ability of humans to migrate, colonise and expand can be gleaned from more detailed analysis of the few percent of genetic variation between human and great ape DNA. Although we are so closely related to chimpanzees (with 95% of our DNA sequence being identical), the remaining 5% still corresponds to over 35 million differences at the level of the smallest building blocks of DNA. Thus, while immensely powerful, one limitation of comparative genomic approaches is the vast amounts of data generated.

Other natural sciences have been consulted to further unravel our ideas of humanness and provide clues as to how these characteristics evolved. To this end, a series of human specific traits have been proposed such as cognitive ability, language and ageing. In addition, human specific diseases, such as Alzheimer's disease or susceptibility to HIV/AIDS or malaria could give us some clues, but they are genetically complex and difficult to unravel.

Our ideas of what are the traits that make us look, behave and act human, have been continually re-evaluated and modified in light of further data. Some traits originally thought to be human-specific (such as the fabrication and use of tools) have since been shown to extend to ape species and have been dropped as candidates for which to identify human-specific genetic components. An area that shows promise is the creation and use of language. Although the most basic capacity is shared with chimps, the use of language to communicate has been substantially refined and extended by humans. An exciting genetic determinant, the FOXP2 gene, is now known to be important in the acquisition and use of language in humans. Its impairment in human individuals has been associated with abnormalities in certain facets of their use of language and the gene appears to have co-evolved with the evolution of human language capacity. The molecular roles of FOXP2 are complex, wide-ranging and still poorly understood. Prof. Pääbo suggests that collaboration with certain areas of the humanities might aid in identifying whether FOXP2 plays a role in other human-specific traits.

An important contribution to understanding the genetic heritage of the modern humans came from investigating the Neandertals, who existed widely on the European and African continents before the first modern humans arrived. It used to be generally thought that the Neandertals were the direct ancestors of modern humankind. Data found by Prof. Pääbo's group indicates that early humans did not interact genetically with the pre-existing Neandertals, meaning there was no inter-mating. This data independently corroborates conclusions reached by archaeologists regarding the behaviour of the early humans and Neandertals. The convergence of findings from comparative genetics and archaeology to answer questions about early human evolution, highlight the strength of inter-disciplinary communication and cooperation.