Viewpoint: Has 'one species' idea been put to bed?
- 30 December 2011
- From the section Science & Environment
Here, Prof Clive Finlayson looks back at the year's developments in human evolution research and asks whether recent discoveries rule out a well known idea about our ancestors.
Hobbits on Flores, Denisovans in Siberia, Neanderthals across Eurasia and our very own ancestors.
Given this array of human diversity in the Late Pleistocene, we might well be forgiven for thinking that Ernst Mayr's contention that "in spite of much geographical variation, never more than one species of man existed on Earth at any one time" had finally been put to bed.
It now seems that a high degree of diversity was also present in the Middle Pleistocene, revealed in the latest analysis of human teeth from that period.
Mayr, one of the great evolutionary biologists of modern times, proposed his single species idea in a Cold Spring Harbor Symposium, published in 1950.
The idea of a single species of human has received a great deal of criticism since Mayr's day but it has also had its vociferous advocates.
So, can we really conclude that the concept was fundamentally flawed on the basis of all the new - fossil and genetic - evidence? That depends on how we understand and define species.
For biologists, like Mayr, species are entities composed of individuals that, in the wild, reproduce among themselves but not with other species.
But palaeontologists use other definitions of species and these have allowed them to classify fossils that cannot be otherwise categorised on the basis of Mayr's biological species concept.
What the palaeontologists call species are essentially divergent lineages but we cannot know whether these had reached levels of genetic independence or not.
Mayr recognised that there had been "much geographical variation" in humans but he just did not think that such variation had led to new species. So the apparently polarised positions are not really that far apart. Enter genetics.
The Neanderthals have long been the "controls" in the human experiment; those we have chosen to compare and, mainly, contrast with the human model. Drawing distinctions between "them" and us has helped in creating a sense of the uniqueness of our condition and it has been natural that we should regard them as a different species.
But now we know that Neanderthals and our ancestors exchanged genes so, using the biological species definition, they must have been the same species. But they had diverged for over half-a-million years: they were distinct lineages which would make them distinct palaeontological species.
And it seems they were not the only ones to exchange genes with our ancestors. The enigmatic Denisovans (still awaiting scientific nomenclature) also exchanged genes with some of our ancestors and they ranged widely.
So the paradox "one species-many species" depends very much on perspective and there is little, it would seem, that contradicts Mayr's contention of geographical variation in a single biological species.
While all this has been happening, more and more papers are being published that are breaking down the differences between Neanderthals and our ancestors.
Now it seems that Neanderthals beach-combed for molluscs as far back as our own ancestors did (around 150 thousand years ago along the Mediterranean coast of Spain), so a defining feature of our modernity and geographical expansion has been eroded.
Stalwarts have been left with our superior cognition, expressed via symbolism, as the last bastion that separates us from the Neanderthals. But even here recent papers suggest that Neanderthals used coloured pigments and may have even worn raptor feathers!
The historical downgrading of our Neanderthal cousins has gone well beyond the scientific. Neanderthals still remain, in many people's minds, the archetypal brutes. But this popular view is gradually changing as scientists are recognising the need to put new ideas across to a wider public.
A meeting in the Neander Museum, near Dusseldorf in Germany, last October brought together scientists and managers from across Europe in an effort to create a network of sites and museums that tell the story of humans in the Pleistocene of Europe.
The Neander site gave its name to their human namesakes but an earlier skull had been found, in 1848, in Gibraltar and went unrecognised.
Work in Gibraltar, the last known place where Neanderthals survived, has changed our understanding of Neanderthal ecology and a key site on the Rock - Gorham's Cave - has now been included in the United Kingdom's Tentative List for World Heritage nomination.
It is recognition that the human evolution story, and the Neanderthals, are very much part of our global heritage. Gibraltar plans to do more as it pioneers the combination of research with public access.
The recently elected Government included in its manifesto a commitment to commemorate the site of the 1848 discovery and there are also plans to develop a unique thematic "Neanderthal Park", the first of its kind in the world.
And a major conference is planned for September next year when experts from all over the world will meet in Gibraltar to revise our ideas about "the human niche". After decades of bad press we are finally getting round to humanizing the enigmatic Neanderthals.