Posts Tagged ‘Neanderthals’

A jawbone with a Neanderthal for a great-great-grandmother

May 30, 2015

That humans today have genes from Neanderthals, Denisovans and some other ancient cousin species seems to be quite clear from the genetic evidence (though I am always quite amazed at the wondrous ability to extract DNA from ancient bones). In fact, it seems that the mainstream of AMH had various breeding encounters with these other species at many different times and (presumably) at many geographic locations. These encounters could not have been rare isolated events suggesting that there was more than a little promiscuity in the pleistocene.

Gene flow in the late pleistocene (Kay Prüfer et al)

It has been thought that most of the Neanderthal/AMH interactions must have taken place in the Middle East or central Asia, but new work indicates that these interactions took place in Europe as well. DNA analysis of a jawbone from a Romanian cave from about 40,000 years ago had a Neanderthal for a great-great- grandparent.

I take this grandparent to be a Neanderthal grandmother who was abducted by some marauding group of promiscuous humans only because the ensuing child survived to give rise to us and it is the human environment which has continued. The picture I have is that our Neanderthal genes today are due mostly to the Neanderthal females who were “impressed” into service by an aggressive and expanding human population. There may well have been Neanderthal male – human female offspring but they would more likely have been brought up in a Neanderthal environment, which – along with them -has not survived.

Ewen Callaway reports in Nature News:

Early European may have had Neanderthal great-great-grandparent

One of Europe’s earliest known humans had a close Neanderthal ancestor: perhaps as close as a great-great-grandparent.

The finding, announced on 8 May at the Biology of Genomes meeting in Cold Spring Harbor, New York, questions the idea that humans and Neanderthals interbred only in the Middle East, more than 50,000 years ago.

Qiaomei Fu, a palaeogenomicist at Harvard Medical School in Boston, Massachusetts, told the meeting how she and her colleagues had sequenced DNA from a 40,000-year-old jawbone that represents some of the earliest modern-human remains in Europe. They estimate that 5–11% of the bone’s genome is Neanderthal, including large chunks of several chromosomes. (The genetic analysis also shows that the individual was a man). By analysing how lengths of DNA inherited from any one ancestor shorten with each generation, the team estimated that the man had a Neanderthal ancestor in the previous 4–6 generations. (The researchers declined to comment on the work because it has not yet been published in a journal).

……. All humans who trace their ancestry beyond sub-Saharan Africa carry a sliver of Neanderthal DNA — around 1–4% of their genomes. Researchers have long thought it most likely that early humans exiting Africa interbred with resident Neanderthals somewhere in the Middle East around 50,000—60,000 years ago, before travelling on to Asia, Europe and the rest of the world.

That possibility has gained support in the past year. Last year, a team that included Fu used the genome of a 45,000-year-old human from Siberia to date his Neanderthal ancestors to between 50,000 and 60,000 years ago (when modern humans were probably starting to leave Africa)2. Another reported finding the 55,000-year-old partial skull of a human in an Israeli cave not far from sites at which Neanderthals lived around the same time3.

But radiocarbon dating of remains from sites across the continent suggests that humans and Neanderthals lived together in Europe for up to 5,000 years in some areas — plenty of time for them to have met and interbred there, too.

But the AMH / Neanderthal co-existence was not a short-lived thing.

Encounters between AMH and Neanderthals probably took place at different times in different places to leave the genetic signal of some 3% Neanderthal genes in non-African AMH. Early encounters would have taken place in central Asia (perhaps 50,000 years ago) with later encounters in Europe (c. 30,000 years ago). Now new methods of radiocarbon dating at archaeological sites is providing evidence which indicates that Neanderthals and AMH overlapped for many hundreds of generations.

 

 

On when speech may have originated

March 3, 2014

A new paper suggests that the Kebara 2 Neanderthals, some 60,000 years ago, not only had the capability but also used speech. The capability for speech itself has now been pushed back to the common ancestors of Anatomically Modern Humans, Neanderthals and Denisovans to about 500,000 years ago. The picture we have of Neanderthals is now of a fairly sophisticated and complex species:

  1. Neanderthals may have spoken in a similar way to modern humans.
  2. Neanderthals are our closest extinct human relatives.
  3. Neanderthal DNA is over 99% identical to modern human DNA.
  4. Several theories for Neanderthal extinction exist, including impacts of climate change, competition with human beings, and the possibility that Neanderthals and humans interbred and were ‘absorbed’ into the human species.
  5. Neanderthals lived in Eurasia 200,000 – 30,000 years ago in the Pleistocene Epoch
  6. Neanderthals and our human ancestors lived on Earth at the same time.
  7. Neanderthals lived in family groups and looked after their sick and infirm. 
  8. Neanderthals used tools made from bone, stone, antlers and other materials. 
  9. Neanderthals used fire, and even ate cooked vegetables. 

Moreover it is clear that all non-Africans carry some 3% of Neanderthal genes. And so – in my speculation – it would be perfectly consistent with not only the Neanderthals of the Kebara 2 study having speech, but also with all Neanderthals from about 200,000 years ago, having some form of – at least – rudimentary speech.

I have no doubt that speech originated from an intense need to communicate and developed in complexity and sophistication as the complex needs of the societies that developed required more nuanced communication. And if this happened 500,000 years ago then I find it not implausible that there are connections between the controlled use of fire, the growth of complex social interactions, the need for nuanced communications and the development of speech.

Visions arise of camp fires and a society with time for gatherings and then – inevitably – for story-telling! And for tall tales. Lying after all is a construct of language!

But speech was probably invented many times and only became language when some critical mass of people shared the same sounds for the same meanings. Within a single tribe or troop this critical mass for the beginnings of a rudimentary language was probably no more than a handful of individuals. What the first words ever spoken were can only be a matter of speculation. A case can be made for the “ma”, “ba” and “pa” sounds being the first to be repeated but also among the earliest ever words for communication would have been danger, here, there, up, down, you, me, stop, come and go.

Neanderthal genes are everywhere

January 30, 2014

Neanderthal genes are everywhere

We seek them here, we seek them there,

We met them often – but when? And where?

They are in our skins and in our hair,

Neanderthal genes are everywhere

From, Sriram Sankararaman et al, The genomic landscape of Neanderthal ancestry in present-day humansNature, 2014; DOI:10.1038/nature12961

Harvard Press ReleaseRemnants of Neanderthal DNA in modern humans are associated with genes affecting type 2 diabetes, Crohn’s disease, lupus, biliary cirrhosis and smoking behavior. They also concentrate in genes that influence skin and hair characteristics. At the same time, Neanderthal DNA is conspicuously low in regions of the X chromosome and testes-specific genes.

Human evolution as a braided stream rather than a branching tree

January 4, 2014
An interspecies love child? from Nature (Christoph P.E. Zollikofer)

An interspecies love child? from Nature (Christoph P.E. Zollikofer)

The genetic history of modern humans is creating a vast jigsaw puzzle. Genetic evidence is mounting that most people today carry some Neanderthal genes, that some carry what have been labelled “Denisovan” genes, that Denosivans and Neanderthals not only had a common ancestor but that there also was admixture between some Denisovans and some Neanderthals and that there was at least one other as yet unnamed archaic honim which interbred with the Denisovans. It now becomes clear that viewing all these various archaic humans as different species could be wrong. They could all well be the same species.

Chris Finlayson reviews the  paleoanthropology advances during 2013:

The conclusion of the Dmanisi study was that the variation in skull shape and morphology observed in this small sample, derived from a single population of Homo erectus, matched the entire variation observed among African fossils ascribed to three species – H. erectus, H. habilis and H. rudolfensis.

The five highly variable Dmanisi fossils belonged to a single population of H. erectus, so how could we argue any longer that similar variation among spatially and temporally widely distributed fossils in Africa reflected differences between species? They all had to be the same species. 

I have been advocating that the morphological differences observed within fossils typically ascribed to Homo sapiens (the so-called modern humans) and the Neanderthals fall within the variation observable in a single species.

It was not surprising to find that Neanderthals and modern humans interbred, a clear expectation of the biological species concept. …. If the fossils of 1.8 or so million years ago and those of the more recent Neanderthal-modern human era were all part of a single, morphologically diverse, species with a wide geographical range, what is there to suggest that it would have been any different in the intervening periods?

Probably not so different if we take the latest finds from the Altai Mountains in Siberia into account. Denisova Cave has produced yet another surprise, revealing that, not only was there gene flow between Neanderthals, Denisovans and modern humans, but that a fourth player was also involved in the gene-exchange game.

The identity of the fourth player remains unknown but it was an ancient lineage that had been separate for probably over a million years. H. erectus seems a likely candidate. Whatever the name we choose to give this mystery lineage, what these results show is that gene flow was possible not just among contemporaries but also between ancient and more modern lineages.

Just to show how little we really know of the human story, another genetic surprise has confounded palaeoanthropologists. Scientists succeeded in extracting the most ancient mitochondrial DNA so far, from the Sima de los Huesos site in Atapuerca, Spain.

The morphology of these well-known Middle Pleistocene (approximately 400,000 years old) fossils have long been thought to represent a lineage leading to the Neanderthals.

When the results came in they were actually closer to the 40,000 year-old Denisovans from Siberia. We can speculate on the result but others have offered enough alternatives for me to not to have to add to them. The conclusion that I derive takes me back to Dmanisi: We have built a picture of our evolution based on the morphology of fossils and it was wrong.

Some time ago we replaced a linear view of our evolution by one represented by a branching tree. It is now time to replace it with that of an interwoven plexus of genetic lineages that branch out and fuse once again with the passage of time

A braided stream rather than the branches of a tree is the better analogy where  – as John Hawkes describes it:

The “braided stream” analogy captures different information about human origins than the usual branching tree. The branches of a tree do not reconnect with each other above the point where they initially separate. A tree will never admit to exchanging sap between its branches, and there are no little xylem hyphae between branches to carry sap anyway. Our evolution was truly a network in which multiple populations existed and contributed to our process of adaptation.

But the braided stream is not quite satisfactory for the picture that is emerging:

promiscuity in the pleistocene

John Hawkes again:

I admit that the braided stream is not a perfect analogy. Diverging rivulets within a valley almost always come together again, forming a complicated network as they form sandbars and islets. None of them flow into a cul-de-sac. Some human populations of the past did become extinct, they did not inexorably flow back into the mainstream of our evolutionary history. Some of them may have flowed back into the mainstream only through very small channels of genetic exchange. When we go far enough back, some populations really did branch off into their own direction. It’s just not clear yet which populations those were. Maybe an evolutionary swamp would be a better analogy, full of algae-covered bayous.

I like the braided stream, and it’s clear that its time has come. Ancient DNA has begun to show the process of genetic exchange was not a minor player in our evolution. All human populations today evidence some mixture of ancient populations that existed well before the “origin of modern humans”. Genetic exchanges between different populations were dominant in the formation of some human adaptations. Some ancient populations can be understood only as the mixed descendants of other, yet more ancient ones. It’s mixing all the way back.

braided-stream-leone

A braided river from http://cloudman23.wordpress.com/ Image – Yann Arthus-Bertrand

The story will most likely become much more complex – as further pieces of the jigsaw are revealed – before the whole picture can be seen But it is already becoming apparent that the origin of modern humans includes genetic exchange with many “species” supposed to have predated AMH and this exchange was not insignificant.

Perhaps the concept of “Anatomically Modern Humans” has to be expanded and pushed back in time. Rather than an origin some 200,000 years ago the start of “modern humans” could need to be pushed back to about 500,000 years ago and has to somehow bring Neanderthals and Denisovans (and some others) back into the fold.

And maybe our ancestors of 20,000 generations ago were just as shocked at a Denisovan-Neanderthal marriage as some in India are today at an “inter-caste” marriage!


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