Svante Pääbo: The man rewriting human evolution-The New Scientist Mag

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Svante Pääbo: The man rewriting human evolution
05 September 2011 by Alison George

He has already revealed that early humans interbred with Neanderthals and discovered a whole new type of hominin from its DNA alone. Now Svante Pääbo is setting his sights on even more exotic discoveries. He tells Alison George why he thinks the bombshells will keep coming

Last year you revealed a previously unknown type of hominin, called the Denisovans, from DNA in a pinkie bone found in a cave in Denisova, Siberia. Tell me about this.
We knew people had lived in this cave, but thought they were either Neanderthals or modern humans. When we sequenced the DNA, I was in the US so a postdoc called me to tell me the results. He said: "Are you sitting down?" because it was immediately clear this was some other form of human; not a Neanderthal, not a modern human. We were totally shocked.

This is the first time that a new form of human has been defined totally from molecular data, not from the morphology of fossils. I think this will happen much more in the future - that just from a tiny speck of bone we can determine the whole genome and reconstruct much of the history.

You recently visited this cave. What was it like?
The cave is in the Altai mountains in central Asia and it was the first time I had seen it. It is really beautiful. It's big, almost cathedral-like with light coming in through a natural chimney. And you know that in this cave there have been both the Denisovans and modern humans and perhaps Neanderthals too. I went there for a meeting where anatomists, palaeontologists and archaeologists came together for the first time to try to sort out what we can say about this group of humans.

Aside from their genome, do we know anything about the Denisovans?
We know that the Denisovans are a sister group to Neanderthals and that the two populations diverged at least 200,000 years ago. We also know that modern humans interbred with Denisovans since around 5 to 7 per cent of the DNA from Melanesian people comes from Denisovans.

The only other thing we know is that a tooth found in the Denisova cave contains Denisovan DNA and it is very large. It looks very different from Neanderthal teeth and the teeth of modern humans. The palaeontologists say that if they had to guess, they would say it is from an older type of hominin such as African Homo erectus. This raises the possibility that Denisovans retained features that were lost in Neanderthals and modern humans, or that Denisovans interbred with an even more ancient hominin.

A toe bone has also been found in the Denisova cave and I understand that you are analysing the DNA. Can you tell me what you have found?
We are working on it but are not ready to talk about any results yet. The first question is if the toe bone is from a Denisovan individual, as one would expect from where it was found.

Does the discovery of the Denisovans raise the possibility that we once shared the planet with other types of extinct human?
Yes. I wouldn't say that's impossible but I would still guess that there would be a limited number. At the time when modern humans came out of Africa, say 50,000 years ago, what was around? Well, we know there were Neanderthals and Denisovans, and we know there were "hobbits", or Homo floresiensis, the short hominins discovered on the Indonesian island of Flores in 2003. So there were at least three forms. Maybe there were a couple more, it's possible. We will know when we have studied more sites.

Thousands of human bones discovered in China and south-east Asia have yet to be analysed. Are you working on them?
Yes. There are a lot of bones in China that are very unclear morphologically and people say that some look a bit like Neanderthals. We of course don't know what the Denisovans looked like. So, yes, I think China is an extremely interesting place to look.

Are you also trying to sequence the genome of H. floresiensis?
Well, getting access to bones has been so political. I would think that the biggest chance we have is to find fossils of them on other islands close to Flores. A few years ago we did get a sample from the root of a tooth but were not able to find any useful DNA. The preservation of DNA is not good there - it's very humid and hot, so it will probably be very difficult to find a sample with preserved DNA.

That must be frustrating.
Yes. But you shouldn't forget that most sites do not yield DNA. When it comes to preserving ancient DNA, the cooler and drier the climate, the better. Acid conditions are very bad. Caves are good places. You have to be very lucky.

Do you have a hunch about whether H. floresiensis is another type of human or a pygmy form of modern human?
I have no hunch. If one reads the literature it seems quite clear now from their morphology that they are an early divergence from modern humans. And they are not just a pathological type of modern human. Perhaps they are a dwarfed form of H. erectus. Since we don't know what Denisovans looked like, maybe they are dwarfed Denisovans.

Where do you think we will be in 20 years' time, in terms of understanding human evolution through the study of ancient genomes?
I think that for sure we will have studied early modern humans, particularly the ones in Africa and the earliest people coming out of Africa to Europe or Asia, for example, Cro-Magnon in Europe. We will know about the variation in the genomes of Neanderthals, in Denisovans, in the early modern humans through time.

So far you have only sequenced about half the Neanderthal genome. Will we have a complete sequence?
Yes, and we will be able to follow changes in the genome across time, before and after glaciation, to discover their population history. We will have defined very clearly what in our genomes come from Neanderthals.

One interesting question is this: people of non-African descent have in the order of 1 to 4 per cent of Neanderthal genome in theirs, but they don't all have the same pieces. So can we puzzle together the whole Neanderthal genome by looking at different people actually alive today, not from fossils?

Your work raises some interesting questions about what it means to be human. Do you ever wonder what the world would be like if Neanderthals had survived?
I think it's a fascinating thing to think that, with just 2000 more generations, Neanderthals would still be here with us. Would they live in suburbia or would they live in a zoo? How would we deal with them? Perhaps racism against Neanderthals would have been even worse than the racism we experience today, because they were truly different from us in some respects.

Or would having another form of humans around have allowed us to be more open-minded and not make this enormous distinction we make between humans and animals today? No one can know, but it's interesting to speculate.


Profile

Svante Pääbo directs the department of genetics at the Max Planck Institute for Anthropology in Leipzig, Germany. Born in Stockholm, Sweden, he is famous for his work on ancient genomes and the "language gene" FOXP2. He is the son of Nobel prize-winning biochemist Sune Bergström