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View Full Version : Relatives of Modern Humans, the Denisovans, crossed Marine barriers before we did.



Flying Purple People Eater
15th November 2013, 07:12
http://www.adelaide.edu.au/news/news65482.html

http://i2.cdn.turner.com/cnn/2011/images/07/20/t1larg.neanderthal.gi.afp.jpg
Reconstruction of a Neanderthal, close relative of Modern Humans and closer relative of Denisovans, in the pose of 'the thinker'.


Mysterious ancient human crossed Wallace's Line



Friday, 18 October 2013
Scientists have proposed that the most recently discovered ancient human relatives - the Denisovans - somehow managed to cross one of the world's most prominent marine barriers in Indonesia, and later interbred with modern humans moving through the area on the way to Australia and New Guinea.

Three years ago the genetic analysis of a little finger bone from Denisova cave in the Altai Mountains in northern Asia led to a complete genome sequence of a new line of the human family tree - the Denisovans. Since then, genetic evidence pointing to their hybridisation with modern human populations has been detected, but only in Indigenous populations in Australia, New Guinea and surrounding areas. In contrast, Denisovan DNA appears to be absent or at very low levels in current populations on mainland Asia, even though this is where the fossil was found.

Published today in a Science opinion article, scientists Professor Alan Cooper of the University of Adelaide in Australia and Professor Chris Stringer of the Natural History Museum in the UK say that this pattern can be explained if the Denisovans had succeeded in crossing the famous Wallace's Line, one of the world's biggest biogeographic barriers which is formed by a powerful marine current along the east coast of Borneo. Wallace's Line marks the division between European and Asian mammals to the west from marsupial-dominated Australasia to the east.

"In mainland Asia, neither ancient human specimens, nor geographically isolated modern Indigenous populations have Denisovan DNA of any note, indicating that there has never been a genetic signal of Denisovan interbreeding in the area," says Professor Cooper, Director of the University of Adelaide's Australian Centre for Ancient DNA. "The only place where such a genetic signal exists appears to be in areas east of Wallace's Line and that is where we think interbreeding took place - even though it means that the Denisovans must have somehow made that marine crossing."

"The recent discovery of another enigmatic ancient human species Homo floresiensis, the so-called Hobbits, in Flores, Indonesia, confirms that the diversity of archaic human relatives in this area was much higher than we'd thought," says Professor Stringer, Research Leader in Human Origins, Natural History Museum, in London. "The morphology of the Hobbits shows they are different from the Denisovans, meaning we now have at least two, and potentially more, unexpected groups in the area.

"The conclusions we've drawn are very important for our knowledge of early human evolution and culture. Knowing that the Denisovans spread beyond this significant sea barrier opens up all sorts of questions about the behaviours and capabilities of this group, and how far they could have spread."

"The key questions now are where and when the ancestors of current humans, who were on their way to colonise New Guinea and Australia around 50,000 years ago, met and interacted with the Denisovans," says Professor Cooper.

"Intriguingly, the genetic data suggest that male Denisovans interbred with modern human females, indicating the potential nature of the interactions as small numbers of modern humans first crossed Wallace's Line and entered Denisovan territory."

Incredible. The mysteries surrounding our closest relatives has gotten me really damn interested in anthropology as of late.

I honestly wonder if (big if here) the cultures of the Denisovan inhabitants of Sahul were passed on to the people who came to live with them - could some cultures in PNG trace back to pre-human society? That would be absolutely amazing if true.

Lily Briscoe
15th November 2013, 08:03
This is interesting, but...

I remember a couple years ago when the Neanderthal genome was sequenced and it was found that non-African humans had some DNA in common with Neanderthals and all this stuff came out supposedly proving that Neanderthals and humans interbred after humans migrated out of Africa. And then more recently this was looked at more in-depth (I think it was last year) and the conclusion was that the percentage of DNA some human populations have in common with Neanderthals was actually consistent with what you would expect simply based on the fact that humans and neanderthals share a common ancestor, rather than being the result of 'mixing' (can't remember how the absence of this DNA in African populations was explained, tho). I'm obviously not an expert (just find this stuff really interesting), but I wonder if a similar explanation could apply here?

Flying Purple People Eater
15th November 2013, 08:16
This is interesting, but...

I remember a couple years ago when the Neanderthal genome was sequenced and it was found that non-African humans had some DNA in common with Neanderthals and all this stuff came out supposedly proving that Neanderthals and humans interbred after humans migrated out of Africa. And then more recently this was looked at more in-depth (I think it was last year) and the conclusion was that the percentage of DNA some human populations have in common with Neanderthals was actually consistent with what you would expect simply based on the fact that humans and neanderthals share a common ancestor, rather than being the result of 'mixing' (can't remember how the absence of this DNA in African populations was explained, tho). I'm obviously not an expert (just find this stuff really interesting), but I wonder if a similar explanation could apply here?

Possibly, although I believe they got the results of Neanderthals from a sequencing of the full Neanderthal genome. I'm honestly not an expert either, but I have heard that the reason most ethnic groups of people in sub-saharan Africa do not have a small amount of Neanderhal in their genome (apparently some groups such as Yoruba and Hausa people do) is simply because Neanderthals never entered Africa. However, I have read that some people believe that, via DNA analysis there may have been a third non-human homo species active in parts of central Africa (parts of the congo maybe?) that may have interbred with people and contributed similarly to the human genome as Neanderthals and Denisovans. Apparently most of the genome percentage inherited from these non-humans was either junk or coding for resistance to particular diseases.

I echo the lament of a certain paleontologist who was involved in the Denisova cave findings - contrary to belief of races and other 19th century silly stuff, we humans are really quite lonely now in the department of super-intelligent primates. :(

ÑóẊîöʼn
15th November 2013, 16:44
This is interesting, but...

... more recently this was looked at more in-depth (I think it was last year) and the conclusion was that the percentage of DNA some human populations have in common with Neanderthals was actually consistent with what you would expect simply based on the fact that humans and neanderthals share a common ancestor, rather than being the result of 'mixing' (can't remember how the absence of this DNA in African populations was explained, tho).

I've never heard of this before. Who said it?

Lily Briscoe
15th November 2013, 17:10
I've never heard of this before. Who said it?
http://www.sciencedaily.com/releases/2012/08/120813155521.htm

Lily Briscoe
20th November 2013, 23:07
Also sort of relevant, from yesterday:



Nov. 19, 2013 — Ancient viruses from Neanderthals have been found in modern human DNA by researchers at Oxford University and Plymouth University.

The researchers compared genetic data from fossils of Neanderthals and another group of ancient human ancestors called Denisovans to data from modern-day cancer patients. They found evidence of Neanderthal and Denisovan viruses in the modern human DNA, suggesting that the viruses originated in our common ancestors more than half a million years ago.

This latest finding, reported in Current Biology, will enable scientists to further investigate possible links between ancient viruses and modern diseases including HIV and cancer, and was supported by the Wellcome Trust and Medical Research Council (MRC).

Around 8% of human DNA is made up of 'endogenous retroviruses' (ERVs), DNA sequences from viruses which pass from generation to generation. This is part of the 90% of our DNA with no known function, sometimes called 'junk' DNA.

'I wouldn't write it off as "junk" just because we don't know what it does yet,' said Dr Gkikas Magiorkinis, an MRC Fellow at Oxford University's Department of Zoology. 'Under certain circumstances, two "junk" viruses can combine to cause disease -- we've seen this many times in animals already. ERVs have been shown to cause cancer when activated by bacteria in mice with weakened immune systems.'

Dr Gkikas and colleagues are now looking to further investigate these ancient viruses, belonging to the HML2 family of viruses, for possible links with cancer and HIV.

'How HIV patients respond to HML2 is related to how fast a patient will progress to AIDS, so there is clearly a connection there,' said Dr Magiorkinis, co-author of the latest study. 'HIV patients are also at much higher risk of developing cancer, for reasons that are poorly-understood. It is possible that some of the risk factors are genetic, and may be shared with HML2. They also become reactivated in cancer and HIV infection, so might prove useful as a therapy target in the future.'

The team are now investigating whether these ancient viruses affect a person's risk of developing diseases such as cancer. Combining evolutionary theory and population genetics with cutting-edge genetic sequencing technology, they will test if these viruses are still active or cause disease in modern humans.

'Using modern DNA sequencing of 300 patients, we should be able to see how widespread these viruses are in the modern population. We would expect viruses with no negative effects to have spread throughout most of the modern population, as there would be no evolutionary pressure against it. If we find that these viruses are less common than expected, this may indicate that the viruses have been inactivated by chance or that they increase mortality, for example through increased cancer risk,' said Dr Robert Belshaw, formerly of Oxford University and now a lecturer at Plymouth University, who led the research.

'Last year, this research wouldn't have been possible. There were some huge technological breakthroughs made this summer, and I expect we'll see even greater advances in 2014. Within the next 5 years, we should be able to say for sure whether these ancient viruses play a role in modern human diseases.'http://www.sciencedaily.com/releases/2013/11/131119230442.htm