Possible new species of human discovered

darjeeling

Svante Paabo's group have just published the complete mtDNA genome of a 30-48,000 year old hominin finger bone from the Denisova Cave in the Altai mountains of Siberia. Using a molecular clock, they estimated that the sequence split from the human lineage around a million years ago, long before modern humans separated from Neanderthals, but also well after the first Homo erectus left Africa.

It's not clear from this alone whether there was a new species of distantly-related hominin that was still living in Siberia until recently, or whether the sequence had jumped through inter-breeding into a Neanderthal or a modern human, both of which were living in the area around the same time. It does, though, suggest that migration from Africa might have been more frequent than previously thought.

There are lots of write-ups around the web, of which this one at genomeweb is good [Edit: but requires registration - d'oh. Fear not - the Times write-up is quite accurate, though in claiming that the bone shows that a new species of hominin was alive 30,000 years ago, it goes further than the evidence sustains for now.] The original paper is in Nature here, with an editorial summary here.

Wibbs

Pretty amazing stuff alright. It would be cool enough if there was a similar genetic drift to the Neandertal/Sapiens one, but a bigger one? Throwing this in with the Flores story and we have at least two out of Africa migrations(possibly 3) previously unknown. Or evidence of interbreeding, maybe even local non African evolution?

Excited though I am about this, I'm still a little dubious about relying on genetic markers. Especially of that great age and of one sample. Or relying on the differences too. We're very homogenous now as a species, but back then we may have been much more diverse, but still one fertile species. Its great stuff though.

BennyLava

Appears that a distinct species of human was wandering round central Asia, possibly as recently as 30,000 years ago

fascinating stuff, how many other lost cousins have we out there awaiting discovery


http://news.bbc.co.uk/2/hi/science/nature/8583254.stm

darjeeling

Thursday's BBC Radio 4's 'Material World' (listen here, or via iTunes) covered the story and interviewed both the paper's lead scientist, Svante Pääbo (to give him all his umlauts*), and Chris Stringer (of the London Nat Hist Museum).

Stringer and Pääbo both said that X woman and the Flores 'hobbits' have overturned the long-held view that there were just two surviving types of hominin a few tens of millennia ago: modern humans and Neanderthals. Both scientists also expect future findings to paint a complex picture of human evolution in the Pleistocene, with populations branching off at different times, and then later coexisting, replacing one another or even interbreeding.

Does X woman represent a new species? Pääbo and Stringer were non-committal, and I'm not sure the question is all that meaningful over these timescales. More pertinently, Stringer said the sequence might have come from very early H. heidelbergensis, thinking that not long after this African hominin had grown recognisably different from H. erectus, some of them may have migrated to Asia. This might, he thought, explain why some unusual Asian fossils seem to have more modern human traits than local descent from early H. erectus immigrants would predict. In Stringer's scenario, later African heidelbergensis would go on to separate into Neanderthals north of the Med, and modern humans south of it, giving the deep phylogenetic split we see between them and X woman.

Pääbo's pioneering work, I think, shows us what we can expect in the coming years. Without DNA, we'd have had just the tip of a little finger that could have been from either human or Neanderthal. DNA, though, shows at a stroke that there were recent Asian hominins with ancestors that left Africa between 0.8 to 1.3 million years ago. We know this because we have a load of modern human mt genomes - some from old bones - and six from Neanderthals. Comparison shows no sharing of mtDNA between the populations, and puts the new sequence on a branch all of its own, closer to the tree root where the chimps diverged. Here's my cartoon version of the complete mtDNA genome phylogenetic tree from the 'X woman' paper:



When we get nuclear genome sequences - both Neanderthal and possibly from the new 'X woman' sample - we'll begin to see whether there was interbreeding between these divergent populations, and to be able to say what proportion of our genes come from each.

As Pääbo tells us, we can't know from either a tiny finger bone or a mitochondrial sequence what the individual who left them looked like. True, but boring. Undaunted, the Guardian tramples over scientific scruples and shows us the face of X woman. Believe it if you will:



Mods: Maybe this thread needs a new title, now that X woman has muscled out the hobbits? Thanks.

* Thanks be to whoever came up with copy and paste, saving me from having to root around the keyboard for all those 'ä's.

Edit: I forgot the link to Ian Sample's Guardian article, which (allowing for artistic licence in the above picture) is good. Here it is.

Galvasean

darjeeling wrote: »

Mods: Maybe this thread needs a new title, now that X woman has muscled out the hobbits? Thanks.

Moved to thread about 'woman X'

I thought I was going to be first in with the scoop only to find you guys discussing it in secret.

marco_polo

Not that we really know how much hair any of these early humans species had given that remains are almost entirely skelatal, but doesn't that artists impression seem a touch on the hairy side by the Guardian?, perhaps by a couple of milllion years I'd reckon.

Still wondering when the full nuclear Neaderthal genome is going to be published, according to New Scientist it was pretty well imminent last December. Although no doubt as DNA amplification techniques are so very sensitive, the result will have to stand up to great scrutiny over even the faintest hint of any possible contamination samples, so it will take as long as it takes I suppose.

darjeeling

marco_polo wrote: »

Not that we really know how much hair any of these early humans species had given that remains are almost entirely skelatal, but doesn't that artists impression seem a touch on the hairy side by the Guardian?, perhaps by a couple of milllion years I'd reckon.

Discreet shading means it's not clear if the picture shows X Woman or X Man, who might be hairier, though we really have little idea what either would look like.

marco_polo wrote: »

Still wondering when the full nuclear Neaderthal genome is going to be published, according to New Scientist it was pretty well imminent last December. Although no doubt as DNA amplification techniques are so very sensitive, the result will have to stand up to great scrutiny over even the faintest hint of any possible contamination samples, so it will take as long as it takes I suppose.

Yes, they're keeping us waiting, and I expect they're keen to make sure the data is beyond reproach.

There was an embarrassment when the first two papers giving small amounts of nuclear Neanderthal genome came out. Starting with the same sample, two groups published very different results. The reason emerged when reanalysis found quite high levels of modern contamination had affected one dataset. Since then, quite a few new techniques have been developed in what is still a very young field, and these should help overcome the contamination problem.

I wonder if Pääbo's group had a look at the nuclear genome sequences they've found so far for the new X woman sample. Pääbo wasn't giving anything away when interviewed, but I'm sure he knows more than he's saying for now.