On the one hand we are being told that human and Neanderthal DNA is about 99% the same -- so that about 1% is different. On the other hand we are being told that about 1- 2% of our DNA came from the Neanderthals. What am I misunderstanding
Photograph Joe McNally, National Geographic
Published January 29, 2014
When modern humans migrated out of Africa some 60,000 years ago, they found the Eurasian continent already inhabited by brawny, big-browed Neanderthals. We know that at least some encounters between the two kinds of human produced offspring, because the genomes of people living outside Africa today are composed of some 1 to 4 percent Neanderthal DNA.
Some parts of non-African genomes are totally devoid of Neanderthal DNA, but other regions abound with it, including those containing genes that affect our skin and hair. This hints that the Neanderthal gene versions conferred some benefit, and were kept during evolution.
"It seems quite compelling that as modern humans left Africa, met Neanderthals, and exchanged genes, we picked up adaptive variants in some genes that conferred an advantage in local climatic conditions," says Joshua Akey, who led the study in Science.
"The adaptive things from Neanderthals are very interesting because they are not obvious," says John Hawks of the University of Wisconsin-Madison, who was not involved in either study. Based on fossil bones alone, anthropologists would never have predicted that Neanderthals contributed to the keratin filaments and immune systems of modern people.
The fact that Neanderthal DNA is totally absent from other stretches of the modern non-African genome suggests that their versions of the genes in these regions would have caused problems in modern humans, and were weeded out by natural selection.
In the Nature study, Sriram Sankararaman and David Reich of Harvard Medical School used the previously sequenced Neanderthal genome to screen 1,004 modern genomes for sequences with distinctive Neanderthal features.
For example, if a fragment of DNA is shared by Neanderthals and non-Africans, but not Africans or other primates, it is likely to be a Neanderthal heirloom. Also, Neanderthal sequences are typically inherited in large batches, since they were imported into the modern human genome relatively recently and have not had time to break apart.
In the Science study, Akey and Benjamin Vernot, both of the University of Washington in Seattle, used similar statistical features to search for Neanderthal DNA in the genomes of 665 living people—but they initially did so without the Neanderthal genome as a reference. They still managed to identify fragments that collectively amount to 20 percent of the full Neanderthal genome.
Neanderthal Influence on Skin, Hair, Common Diseases
Despite their different approaches, both teams converged on similar results. They both found that genes involved in making keratin—the protein found in our skin, hair, and nails—are especially rich in Neanderthal DNA.
For example, the Neanderthal version of the skin gene POU2F3 is found in around 66 percent of East Asians, while the Neanderthal version of BNC2, which affects skin color, among other traits, is found in 70 percent of Europeans.
The Neanderthal version of these genes may have helped our ancestors thrive in parts of the world that they were not familiar with but that Neanderthals had already adapted to. "Neanderthals had been in these environments for hundreds or thousands of years," says Sankararaman. "As modern human ancestors moved into these areas, one way to quickly adapt would be to get genes from the Neanderthals."
"Unfortunately, skin and hair do so many things that it's hard to speculate on what specifically that adaptive trait was," says Akey.
Sankararaman also found Neanderthal variants in genes that affect the risk of several diseases, including lupus, biliary cirrhosis, Crohn's disease, and type 2 diabetes. The significance of these sequences is "even less clear."
Both teams found that non-African genomes have large continuous "deserts" that are totally devoid of Neanderthal DNA. These regions include genes such as FOXP2, which is involved in motor coordination and could play an important role in human language and speech.
The Neanderthal-poor deserts are especially big in the X chromosome, and include genes that are specifically activated in testes. This hints that some Neanderthal genes may have reduced the fertility of male modern humans and were eventually lost. However, Hawks cautions that this probably happened over hundreds of generations—it was very unlikely that the sons of Neanderthals and modern humans were obviously infertile.
DNA Hints at Other Mystery Humans
Both teams are now planning to apply their methods to other hominids like the Denisovans—an enigmatic group whose presence in Asia some 40,000 years ago is known just from DNA from a finger bone and some teeth found in a single cave in Russia.
And Akey's work shows that it may even be possible to partially reconstruct the genomes of unknown groups of ancient humans without any prehistoric DNA samples.
"That's one of the things that I'm most excited about," he says. "Paleogenomics is a difficult field because it often requires finding suitable fossils with well-preserved DNA. "Maybe we're not always beholden to bones. We can look at the genomes of present-day individuals."
It is becoming increasingly clear that the Pleistocene was awash with many different groups of early humans, hooking up with each other to various degrees. Recent studies, for instance, have found tantalizing hints of unknown groups from Asia and Africa that left genes in Denisovans and modern humans, respectively. Akey's method could give us our first glimpse at these mystery humans.
"If there is no fossil evidence and potentially never will be, this will be the only way of finding out about groups that were important in human history," he added.
It is possible that the researchers from Cambridge and UNED were correct and Svante Paabo's team here is, again, wrong in assuming that the presents of Neanderthal DNA in non-African populations means the European & Eurasia migrants mated with this separate species when we arrived. Neanderthal are very different in many ways and it is important we continue to look at those differences instead of just end exploration because of a baseless assumption that were all the same species anyway because of a proven-wrong theory that we mated with this amazing, but radically different species. UNED researches re-dated Neandethal fossils in August of last year and showed they were gone before we got to Europe.
Dr Andrea Manica of Cambridge led a study published in Aug 2013 in PNAS, after the interbreeding bombshell, that proved there was no basis to Paabo's theory because there was a more likely model showing that many groups of modern humans were spread out in Africa, some more closely related to our common ancestor with Neanderthal than others and some of those groups left Africa. You see this same diversity of ancestry in modern primate groups but you can't assume something mated with giraffe every time you see a long neck, so to speak. This is some great science structured around wrong information as often great science is.
Important info here if you can look past the mistake. Dr Manica's model also fits the diverse haploid types of modern humans in Africa and fits the Pleistocene situation in Africa that possibly caused the situation of many closely related groups of hominids and modern humans seemingly living side by side. This Pleistocene circumstance may have been many cycles of geographic isolation and reconnection during each individual glacial where cycles swinging from large to small lakes and rivers pulsed as glacier blocked lakes gave way around Ethiopia and elsewhere. Whatever the cause, diversity of closely related, or same species, hominids , including modern humans, seems to be the tune we are hearing in Africa from almost the last 2 million years. It seems to have accelerated evolution or diversity. You have Homo Heidelberg; Rhodesiensis & Erectus all over Africa at the same 500 to 750 thousand years ago, while they were outside of Africa, too. There may have been transitional species between Neanderthal Ancestor & modern Human from just before that time or something like Erectus and Rhodensiensis giving rise to Neanderthal and Humans, respectively while some groups completing speciation more completely than others. Mating between species just seems like fantastic melodrama that some want to be true despite the science that says otherwise.
The thing about breeding is that the mating pair have to be of the same species to produce offspring which are fertile. Therefore, Neanderthals and "modern humans" are both human. If they are both equally human the distinction between us and them is like the distinction between races of people, nothing more. Neanderthals have just been abosorbed into a collective gene pool.
Seriously doubt it was Neanderthal that contribute disorders like Lupus since there were cases of lupus in Africa as well.
I think modern humans, neanderthals, and other variants, all came from one common ancestor and that some worldwide disaster caused a massive die out, and inbreeding among the few who survived in various pockets around the world.
Geneticists now have shown signs of inbreeding in humans, neanderthals, and denisovans. This new research shows tons of neanderthal DNA in modern humans.
Unfortunately, I think the ice sheets that covered much of the world for many thousands of years have destroyed what evidence we might have found.
Fascinating! For speculation back in 1999 about Neanderthal-modern human relations, see The Silk Code, which “offers a startling hypothesis about modern-day humans and Neanderthals” -NY Timeshttp://www.nytimes.com/books/99/11/28/reviews/991128.28scifit.html#silk
On Denise's point - there are indeed some key fossils in the Levant around 100,000 years ago, notably at Qafzeh and Skhul, and the latter in particular was often thought of as a possible Neanderthal-modern human hybrid. More recently, the very modern-looking Qafzeh material has been viewed as evidence of an earlier "failed" excursion of AMH's out of Africa. And the genetic analysis recently (2012?) done by David Reich et. al. puts the date of interbreeding between Neanderthals and AMH's between 37,000 and 86,000 years ago, suggesting that those 100,000-year old guys were not involved. But it's hardly the last word. It would indeed be sensational to get some DNA out of any of those Middle Pleistocene Levantine hominids... but seems unlikely given the hot climate.
Yes, I concur with what Denise is saying. I would be interested also in some sort of study for those other areas. All you have to do is look at some people and you can see for yourself the genetic codes have been passed down from many generations. Peoples have absorbed the DNA from Neanderthals and Denisovans a long time ago. The dominate genes take over and many of the Neanderthal traits have disappeared but they are still there ( hidden ). They come out every now and again.
It's a stretch limiting this interaction to only 60,000 years. Neanderthals and modern humans were coexisting and likely interbreeding over 100,000 years ago in the Levant. Mount Carmel has Neanderthal remains dating back 120,000 years. There could well have been a long history of interbreeding in that entire region even before homo sapiens started moving into the southern Europe and along the Mediterranean. Neanderthal and modern human burials have been found in close proximity in several area in the Levant -- it would be very interesting to see the results of genetic studies from these remains. There is also the possibility that the 'deserts' in the modern human genome which don't show any Neanderthal genetic heritage could mean that both groups shared in common large vestiges of genetic material from earlier hominid populations. But what I find the most interesting is that 10 years ago, everyone was saying that the Neanderthals were a dead end and had nothing to do with modern human genetics. Big surprise!
After all, what is the difference between the life that is in a cell, a chimp, a neanderthal or a modern homo sapiens? Do not come and vanishes in the same way, in one breath alone? Isn’t life a single indivisible movement, an information flow that stores and changes from a common ancestor? Or is there a unique quality in some place of the tree of life, a qualitative leap detached from all evolutionary processes and unrelated to the rest of life? If so, is it the same leap that the human language makes when differentiating between life itself and the rest of the universe? Also between human beings and the rest of animals, between food and eaters, health and disease, between life and death? Along these lines, there is a peculiar book, if you want there is a preview in http://goo.gl/rfVqw6 Just another suggestion, in order to free-think for a while.
If you translate d'Capatian you get "of the big head" and I believe that to be Neanderthal and or Denisovan. The d'Capatians were the royal families of Europe and the royal families had to protect the blood ..... they were also sire. They understood the importance of protecting the blood line and bringing it into the general human population. Just my opinion, I am 3.5% Neanderthal and 3.4 % Denisovan.
Don’t expect this “science” to sneak its way into the classrooms here in the South. Our Lord and Savior made it very clear there is no way we evolved from these savages. Tennessee has passed the Monkey Law legislation which ensures teachers can challenge these so-called scientists and their twisted research funded by the liberals in Washington. Read about how we’re keep Christ in the Classroom at http://dregstudiosart.blogspot.com/2012/04/pulpit-in-classroom-biblical-agenda-in.html
@Kathleen Cleary Not true all the time. One species of dolphin was found to have risen from interbreeding of two separate species.
For fertlity of the offspring of two separate species, the offspring can only be infertile if the number of chromosomes do not match. But if they did, it is possible to have an offspring who is fertile. The fertile offsprings can be only males or only the females or both sex.
@Kathleen Cleary This is true, if interbreeding happened we would be the same species and the uniqueness of each wouldn't matter that much.
The above article provides some great science but, fortunately, two other important studies show it may be incorrect about the theory of hybridization being the cause of shared DNA.
One study that indicates we could not have interbred was published on Feb 4 of last year in the Journal 'Proceedings of the National Academy of Science' (PNAS). Here, the Department of Prehistory and Archaeology at the Spanish National Distance Education University (UNED) used "ultrafilterration" to clean carbon contaminants that interfered with proper radio carbon dating and found that the extinction of Neanderthal likely happened 50,000 years ago while modern humans didn't leave Africa to settle in the Iberian Peninsula region until 42,000 years ago. In the same journal in August 13 of the same year, Dr Andrea Manica, who led a Cambridge study on this subject said, "Our work shows clearly that the patterns currently seen in the Neanderthal genome are not exceptional, and are in line with our expectations of what we would see without hybridization." Hard to say which researchers are right but the science article in Nature that the above article is based upon, provides as references, some work done by the same authors where the same claims are made. That's like quoting yourself to validate what you are saying. Obviously, I could never dare deny the sensational proof that Neanderthals & Modern Humans did it, because my comment wouldn't be published, but I can say there are some crazy radicals out there that have other, completely unfounded ideas.
@S S It was the genes that increase the risk to having that disease that the article was talking aboutl. We are separate species from dogs and rats, but they do get cancer too. It just that certain gebes make people more at risk to these diseases.
@Paul Seaver How do you find this out?
Lupus affects more people of African descent than any other; therefore the implication is that this genetic contribution effects risk to the benefit of those inheriting it, lowering the chance of Lupus in those populations with the gene in question. They never said any or all of the contributions were negative.
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