Skip to Content

Adding to the sum of our parts

Early humans interbred more than previously thought.
New human relative discovered in Siberia.

We humans like to think of ourselves as being the pinnacle of evolution. We see humanity sitting atop a pyramid made up of all that came before us. At its foundations are the single-celled beasties that kicked it all off, then, as we move up, we pass fish, amphibians, primitive mammals, apes, hominins and so on.

It’s all very neat – every step of our evolutionary journey is separate and compartmentalised – with the inferior giving way to the superior in a neat, linear conveyor belt of succession.

But we are quickly learning that such chronological segregation applies no more to us than it does to any other creature on the planet.

We have known for some time that anatomically modern humans (homo sapiens) shared some time on the planet with Neanderthals. Then came the discovery of a small hobbit race of humans, called Homo floresiensis, which may have been wandering around as recently as 13,000 years ago (although this is still debated). Finally, last year, a discovery was made in a Siberian cave that suggests that, around 40,000 years ago there were at least four separate species of human all knocking around together.

The newly discovered toe bone was found in the Denisova Cave in Siberia. The cave had already yielded a fossil tooth (above) and finger bone, in 2000 and 2008

So far only a tooth, a finger bone and a toe bone have been found in the cave, but DNA analysis has shown that they belong to a previously unknown hominin species – named Denisovans, after the Denisova cave in which they were found.

Suddenly, our evolutionary compartments are looking a bit messy.

To make matter worse, it seems that, as well as living at the same time, at least three of these hominin species were coming into contact and, well, doing the dirty with each other.

[Graphic: Mapping the human cocktail. Click to enlineageate]

In 2009, comparisons with DNA extracted from Neanderthal remains, proved that, in Europe and the Middle East, Homo sapiens had interbred with their ‘primitive’ cousins and left a genetic mark on today’s human populations.

A new study of the Denisovan remains, by the Max Planck Institute for Evolutionary Anthropology in Germany, has revealed that modern human populations in parts of Asia are carrying Denisovan DNA in their genes today – meaning that early Homo sapiens may have notched this species on their bedposts too.

To muddy the waters further, the shape of the Denisovan toe bone, which comes from a separate individual from the earlier tooth and finger remains, seems to suggest that it belongs to a sort of Neanderthal/Denisovan hybrid – meaning that these species were also interbreeding.

So the familiar tale of modern humans leaving Africa and moving to on to take over the world is now looking a little less cut-and-dried. The new tale seems to go a little like this: all four human species have a common ancestor. About half a million years ago, a group of this ancestor left Africa, split up and became Neanderthals and Denisovans – those that stayed behind in Africa became Homo Sapiens (us). When we left Africa about 200,000 years we came into contact with our cousins and fancied a bit rough and the rest, as they say, is history.