We know that we shared Europe with them between 30 and 40 thousand years ago. We know they buried their dead and may have had primitive speech. We even know some of them had red hair like us. Now, genetic research has provided us with evidence that ancestral lineages of modern humans may also have been getting jiggy with the Neanderthals!
Scientists at the Max Planck Institute for Evolutionary Anthropology have announced a completed draft version of the Neanderthal – Homo neanderthalensis – genome with intriguing results and implications. It appears our mysterious relationship with the Neanderthals is set for further speculation.
The team led by Svente Pääbo, head of the Neanderthal genome project, have sequenced four billion base pairs – roughly 1.3 fold coverage of the genome or entire genetic code. The genome was compiled from amplified DNA, extracted from 21 Neanderthal bones taken from four European sites in Croatia, Germany, Russia and Spain.
Once mapped, the Neanderthal genome was then compared to five modern human genomes from individuals of French, Han Chinese, Papua New Guinean, Yoruban (east African) and San (southern African) origin for maximum variation.
Now for the revelation! Analytical tests show that the Neanderthal genome is significantly more similar to the genomes of non-African modern humans than Africans. The most plausible explanation for this is interbreeding between Neanderthals and non-African modern human ancestors, estimated to have occurred between 50 and 80 thousand years ago when populations of the two species overlapped in the Levant, Arabia and the Middle-East. One to four per cent of the Eurasian genome could be derived from Neanderthal sequences.
Pääbo commented that ‘Neanderthals fall into our variation and for some parts of the genome I might be closer to Neanderthals than you.’ Chris Stringer, Palaeoanthropologist from the Natural History Museum, London, reasoned that this could have been ‘small scale interbreeding’ with the signs ‘magnified in modern human populations after they increased in size’
In a currently accepted model called Out of Africa Two, modern humans – Homo sapiens – evolved in Africa in the last 200 thousand years and migrated from the continent some 60 to 80 thousand years ago, replacing remaining archaic populations. Neanderthals are known in the fossil record from around 400 thousand years ago when characteristic features such as their protruding nasal region and brow ridge, receding forehead, bell shaped rib cage and low cranial vault appear, to as recently as 26 thousand years ago from a site in Gibraltar. Out of Africa Two doesn’t predict gene flow between the two species but interbreeding dates following migration are compliant.
The scientists were also able to look for areas of the genome that are unique to modern humans and have been altered since our divergence with our so called ‘cousins’, the Neanderthals. It appears genes related to cognitive abilities, metabolism, cranial and upper body skeletal structure have been under positive selection in Homo sapiens since our split from the Neanderthals sometime within the last 500 thousand years.
Sarah Tishkoff, a geneticist at the University of Pennsylvania, claimed there was ‘no smoking gun – a gene or variant that distinguishes Neanderthals from modern humans, but I think there will be in the future’.
The research has certainly questioned the total replacement model of Out of Africa Two and has placed emphasis on the fossil record to provide us with palaeontological evidence of interbreeding. Contentious fossils showing a mosaic of Neanderthal and modern human characters are known but Stringer added that we should remain ‘cautious’ because they are ‘based on features that occur in low frequency today in modern humans’.
For the orginal paper see Green, R.E et al. 2010. A draft sequence of the Neanderthal genome. Science, 328(5979), pp.710-722. (http://sciencemag.org/special/neandertal/)