Yeah, but that doesn’t mean much - it’s known that Neanderthals had some religious ritual life, so what if, for instance, the cognitive abilities mentioned include those that govern increased group cohesion behaviour but also a slight tendency to religious fanaticism or some such? Or excessive pattern matching leading to possibly scoring better at standardized logic tests, but an increased susceptibility to superstitions and conspiracy theories?
Neither of those are a nett positive, in my book. Of course, I like redheads a lot, so it’s possible the European half of my ancestry is a hopelessly Neanderphilic one already.
I think the abstract and the article content make it fairly clear that this is not correct. The article is about, as the title says, “A Draft Sequence of the Neandertal Genome”. The authors are making two separate major claims for their results:
that they have identified genomic regions where they can compare Neandertals to early modern humans as a whole to detect post-divergence changes in human characteristics caused by positive selection; and
that genetic similarities between Neandertals and modern humans are different depending on where the modern humans come from.
In short, having a draft sequence of the Neandertal genome allows us to see both how early modern humans as a separate species changed after separating from their Neandertal cousins, and how certain modern humans are nonetheless more like Neandertals than other modern humans are.
The last two sentences in the article abstract make this very clear:
That’s my statement (1): ancestral modern humans evolved into a separate species from Neandertals due to positive selection pressures on characteristics including metabolism and cognitive and skeletal development.
That’s my statement (2): ancestral modern humans were not all equally different from Neandertals, either because the ancestral Eurasians hadn’t initially evolved away from shared human-Neandertal characteristics as much as the ancestral Africans had, or because the ancestral Eurasians interbred to some extent with Neandertals after leaving Africa.
The meaning of statement (1) is further clarified by the authors’ remarks on page 716:
Namely, they looked for genetic features that were present in a common ancestor of all modern humans but not present in Neandertals. That tells us how modern humans as a species evolved due to positive selection effects after the human-Neandertal evolutionary split.
Sure, and so would any non-advantageous genes. More research will be needed to determine precisely whether and how a slight admixture of Neandertal genes makes non-African modern humans detectably different from African modern humans. And it will be very interesting to see what specific effects such genetic differences might have had on the different human populations that experienced them.
But that’s not what the authors of this particular study are talking about when they speak of “positive selection”. That refers to the species-level evolutionary differences they found between Neandertals and all modern humans.
I think your confusion about this may have stemmed from the slant of the popular media story originally cited in the OP, which implied that the only major finding of the Science article was the different levels of Neandertal genes in non-African and African modern humans. The actual article makes it clear that the authors are looking at a much bigger picture.
“Non-advantageous” genes don’t exhibit much “positive selection pressure,” do they? As to the characterization of a 1-3% admixture as “slight,” well it depends on how good the new genes turn out to be. One good cognitive gene might be worth a hundred that code for skin characteristics.
The point of this article, and the reason it’s garnered such widespread notoriety already, is that only the non-Arfrican group of modern humans contain Neandertal genes. Because the Neandertals were a different-enough group and because it has been historically debated whether there could have been inter-mixing, the conclusion of a 1-3% contribution to the modern non-African genome is significant.
I don’t think we’re quite at the point of being able to characterize how much functional significance all those genes have. Like any genetic differences noted at a group level between Africans and non-Africans (microcephalin haplogroup D, e.g.), all but the most robust and rock-solid functional differences are going to be described as “preliminary” or “controversial” or some similar language.
We can argue more about the other point as the authors produce further articles. Looks like they’ve done a fair amount of analysis, and my experience is that research of this magnitude is usually fodder for a whole round of papers examining various fine points. It still seems to me their point (and some of the genes referenced) is that genes involving cognitive and skeletal functions are different in the Eurasian group as opposed to the African group because of the Eurasian group’s admixture of Neandertal contributions to those genes. While it’s true those genes could be “non-advantageous” I’m not sure too many folks would jump to a conclusion that non-advantageous traits would be promoted down the past few thousand years somehow.
I was referring to neanderthals, but I suppose since pretty much every humanoid seems to be shown pretty unkept, I can expand it to every himinid in a display in a museum =)
bling good, ug! Perhaps the indication of humanity isnt building a fire and writing, but killer fashion sense, bling, and makeup!
As I said, even the pretty much naked amazon natives paint themselves up and use feathers, shells and whatever as jewelry. People will decorate themselves if they can find a little mud and something shiny!
OK, seriously. This gets more interesting as I dig into it. As **CP **noted, above, this is very preliminary info, and there is much more to be learned from this analysis as it carries forward. The Neanderthal genome is only 60% complete, and needs to be checked multiple times to weed out errors. I can only hope that we start getting DNA from earlier ancestors or side branches.
This revelation does not at all surprise me. If you’re at all familiar with how horndoggin’ modern humans are, it’s not much of a stretch to imagine our ancestors eyeing a burly Neanderthal glowering at them from under prominant brow ridges, and at least one of them thinking, Yeah, I’d hit it.
Considering only what, a few hundred Neanderthal skeletons have been found, scattered all over the place, I don’t suppose it’s possible to ascertain if any Cro-Magnon/Neanderthal hybrids remained with their Neanderthal brethren rather than being absorbed into the Cro-Magnon population. Aww, now I’m picturing a little hybrid kid cuddling up to its Neanderthal mama.
No, but as I explained, the references to “positive selection” in this article aren’t referring to changes in genes derived from human-Neandertal mixing, but rather to earlier changes in modern humans’ genes in the process of human-Neandertal separating.
As I noted, that is indeed one of the two major points of this article. And you’re right that that point seems to be the only one that the popular media have picked up on. But the article abstract and content make it clear that the article is also discussing the ways in which the draft Neandertal genome sequence can be used to identify species-level genetic differences between Neandertals and modern humans as a whole.
ISTM, for the reasons I explained above, that this interpretation is clearly wrong, at least insofar as it refers to the section on “a screen for positive selection in early modern humans” that I quoted earlier. Can you point to one or more specific statements in the article that you feel justify your interpretation that the references to “a screen for positive selection” are meant to apply to Eurasian-Neandertal interbreeding rather than earlier human-Neandertal divergence?
Why not? There’s nothing in evolutionary biology that says a non-advantageous genetic trait can’t survive in a population, as long as it doesn’t actually impede reproduction. If non-advantageous traits couldn’t persist in a population, that would disprove your own belief that for thousands of years Africans have retained some cognitively disadvantageous traits compared to other modern humans.
There was an article somewhere, Wired maybe, that suggested that Neanderthals didn’t really go extinct, or get killed off or out-competed by homo sapiens, but were absorbed through interbreeding to the point that they were no longer recognizable as a separate species.
Would that be going too far, or is that the amount of interbreeding it would take to have an impact on the homo sapiens genome that is still measurable today? I would think there would be enough social pressure against it to maintain a pure “ethnic” neanderthal population, but maybe not in the face of 20,000 years.
Could this be proved by showing that Caucasians have more Neanderthal genes than Australian Aborigines? As I understand it, Neanderthals were mainly in Europe and Homo Sapiens spread to Australia over 40K years ago, thousands of years before the extinction of the Neanderthals. OTOH maybe the aborigines are partially descended from Homo Floriensis?
The thinking on the basis of this most recent data is that as Homo sapiens came out of Africa they, early on, interbred some with Homo neanderthalensis, and then spread out from there to the rest of Europe and Asia. Homo sapiens then got over to Australia from there. By 30,000 years ago the Neadertals were extinct. The interbreeding event(s) presumably would have taken place before that move into Australia although it is possible that a separate group had moved out towards that direction before the interbreeding event(s) occurred, or that interbreeding events were ongoing, in which case Caucasians would have more Neandertal than Asians who may or may not have more than Australian Aborigines. Still 1-4% Neandertal DNA is not as much as one would expect is the whole population was absorbed. These were not pervasive occurrences but more of a leakage in. And as noted below, the evidence only speaks to one sort of interbreeding occurring.
There was no admixture noted in previous studies of mitochondrial DNA, which had been the basis of the previous belief that it was unlikely significant interbreeding had occurred. Homo sapiens was, presumably, the successful invader. Usually that means raping and pillaging but that would have preserved Neandertal mitochondrial DNA as invading males either rape the conquered or take them as (one of?) their mates (perhaps in a slave type position. These events were at least overwhelmingly male Neadertals mating (consensually or otherwise) with Homo sapien females; pattern had to jibe with that image of Homo sapiens engaging in a successful genocide against the Neandertals. We instead can imagine Homo sapiens just outcompeting the Neandertals and bands of Neandertals running raids in their incampments, raping in the process, or, yes, a few Homo sapien females who found the appeal of the taboo muscular Neandertal enough to have some … relations … with, and who were able to avoid rejection by their own tribe for that action, either by keeping it a secret or by compassion. They make for some interesting stories.
Not really. Without knowing the exact number of Neanderthals vs Moderns in Europe, let’s assume that it was roughly equal at some time. Let’s say there were 50,000 of each. If we have 1-4% Neanderthal ancestors, that means only about 1,000 of those 50,000 Neanderthals were “absorbed” into the invading population of 50,000 Moderns. The rest of those 49,000 Neanderthals left no progeny with ancestors today. And, as you said, after 25 -30k years of the hybrids mixing back into the population of Moderns, the deck gets pretty randomly shuffled.
I hope I don’t look like a dufus here. But the study, as I understand, only compared Neanderthals to five humans from China, France, Africa and Paupa New Guinea. The article goes on to explain that two of the people they examined came from western and southern Africa.
That leaves a grand total of 3 “non-Africans” from which the authors used to conclude that “non-Africans” trace between 1 and 4% of their genes to Neanderthals. The obvious problem here is that their study lacks the power to conclude (or even persuasively suggest) anything about variation in the “non-African” mega-cohort. This seems too important to gloss over like it seems the article did (it actually didn’t acknowledge it as a limitation). The true range could in all probability be higher than 4% or much lower than 1% (like zero); so I puzzle at how these findings provide evidence of where the intermixing occur.
A related critique is that their sample doesn’t come anywhere close to representativeness, so it’s weird that they use these results to distinguish between “Africans” and “non-Africans” as if they do have a representative sample of humans. Northern, eastern, and central Africans were not sampled, and it’s implausible to think they’d be completely cut off from Neanderthal gene flow from the Mid-East. Additionally, 3 people from France, China, and PNG is far from representative of “non-Africa”. It would be interesting to see how peoples in west Asia compare to east Asia, and how these groups compare to people from Greece on up to Norway.
If Neanderthals were absorbed into modern human groups in the mid-East, would we not expect the concentration of these genes to be heaviest in this area and then thin out the farther away we move from the mid-East? Isn’t this how it works with most genes? This would mean north and eastern Africans that have intermixed with borderland peoples could in theory have more Neanderthal genes than an Eskimo or Suede. Does this strike anyone as implausible or contradicted by the evidence that has come out this research?
I think that because the matches are “old lineages”, they are more likely to be shared by everyone in the population studied than would be “newer lineages”.
I admire your doggedness in spinning a tale why Neandertal influence may not be that big of a story*, but as a general rule of thumb, genes that persist over long periods of time are either silent and carried along incidentally (as is probably the case with much of our Neanderthal heritage) or else functional in some positive way. They may be directly functional or they may be indirectly functional, and it can take a long time to sort out just why a particular gene is good for us, as you know.
It’s just plain silly to state that it is my belief Africans have “retained” some “cognitively disadvantageous traits” as if it were my position that Adam and Eve were created de novo perfectly, and some descendant groups deteriorated faster than others. That may be your belief system, but it’s not mine. My position is that where almost any two groups are cognitively different, the explanation lies in genes more than nurture. Period. One reason two groups might have different genes is exposure to gene pools not accessible to the other group; such an event may have happened with Eurasian exposure to Neandertals, but it could certainly have happened other ways. Perhaps a sub-group of Africans with the most advantageous cognitive genes is the one that emigrated; perhaps there were advantageous mutations…
But retaining disadvantageous traits while presumably discarding advantageous ones? That there is the **Kimstu **notion of evolutionary drivers, not the Pedant’s. On average descent with modification is because modification is an improvement in reproductive capacity in some way.
YWTF: the choice of San and Yoruba genotypes as prototypical for “African” is discussed in the article and elsewhere. While the PC crowd wants to leave the public with the impression that we are all about the the same–or at least all differentin about the same ways–in point of fact there is pretty good research in the genetic mapping community which makes those two populations reasonable choices as representative for sub-saharan Africans. Going forward many more populations will be mapped and distinguished, but I haven’t seen any criticisms directed at the use of those two population genotypes as baseline. There may well be African groups with Neandertal genes, of course, but I have not seen much speculation that this will turn out to be so.
DSeid, a note on the mitochodrial DNA: John Hawks thinks Neandertal DNA is gone from modern Eurasions because it conferred a selection disadvantage. See here for that topic (about half-way down) and a number of other interesting notes.
*In one of the side blogs I was reading a reference is made to Leo Szilard’s quip to Jonas Salk about the three stages of truth in science paradigm shifts:
1. It’s not true
2. It may be true but it is of no consequence
3. I have always been aware of this fact.
Right now the genetically egalitarian crowd is at stage two, I’d guess, hoping there is no progression to stage 3. (And of course, there is no data so far showing there will be any such progression. Maybe the Eurasian 1-4% Neandertal contribution will all turn out to be deadweight genes).
As I understand it, the small number of contemporary humans sampled doesn’t present a “small sample size” problem in this case, because the study isn’t comparing individuals but particular population genomes. The San/Khoisan genome, the Yoruba genome, the East Asian genome, the European genome, and the Papuan genome have been sequenced and are known to represent distinct evolutionary branches of modern humans.
It’s like, let’s see, it’s kind of like if researchers decide they want to compare different translation choices in various different versions of the Bible. So they borrow your copy of the King James Bible and my copy of the Revised Standard Bible and John Mace’s copy of the Good News Bible, etc. They end up with only one copy of each version, but it doesn’t mean that their sample size is too small, because the things that they want to compare are identical across all the millions of copies of the same version.
Likewise, in this genetic research it’s adequate to compare only one Yoruba individual with one Papuan individual and one European individual, etc., because individual variation isn’t affecting the genetic characteristics they’re looking at.
As I understand it, though (and I could well be mistaken), the San and Yoruba genomes give pretty good coverage of the genes of never-left-Africa modern human populations (see the tree on p. 1101 of this Science article). If a genetic trait is present in one or more of the Eurasian genomes but not in the San or Yoruba genome, it’s a pretty good bet that it made its appearance outside of Africa.
Not if the Neandertals interbred with Eurasian ancestors soon after their migration out of Africa, while they were all still one group. Then as the group diverged into various branches of Europeans and Asians, they would all keep about the same amount of Neandertal heritage, which is what the study’s authors are arguing is the most likely explanation of their findings.
I wouldn’t say that … just as a random example, if I had a neander grandmother, and she had no other children than my mother, once I die her lineage as determined from maternal mitochondrial DNA is gone … but she did reproduce with a cro magnon … so your concept is flawed. In history many maternal lines died out through lack of progeny/mass death through disease or violence [you know, raid the next village over and kill everybody type crap]
it may be possible that the various plagues and wars in the old world artificially truncated neanderthal maternal lines. They may have been almost totally blended in, just not interpreted correctly.
I really think you’re seriously misunderstanding what I’m saying. I’m not advocating or making any judgements for how “big of a story” the Neandertal genetic links are.
Nor am I suggesting that the Neandertal heritage “retained disadvantageous traits while presumably discarded advantageous ones”. I’m just pointing out that it appears from the current research that whatever Neandertal traits modern humans acquired, whether advantageous, disadvantageous or neutral, were acquired only by the Eurasian “trunk” of the modern human evolutionary tree.
And I don’t understand your complaint about my characterization of your position on African versus non-African genes. AFAICT, you do in fact hold the view that certain differential outcomes for African-descended populations compared to other modern humans are explained by genes for cognition that put those populations at a comparative disadvantage, and that those genetic differences have existed for thousands of years. Is that not an accurate description of your views? In what way have I represented your position incorrectly?
I’m trying to understand how this would logically happen though, given how mutations tend to distribute themselves in populations.
Say you have a few people (human women) stumbling out of Africa into the Mid-East, where they are raped by Neanderthals and give birth to hybrid babies. (The Neanderthals gradually die off for unexplained reasons…maybe the human men are mad about the rapes that occurred and kill them off, or maybe the Neanderthal women keep dying in childbirth or some crazy shit like that.) In this migratory group, you also have humans who don’t interbreed with these Neanderthals. These people either hang around and intermingle with the hybrids, or they trek eastward and northward (or back into Africa), keeping their bloodlines human.
The hybrids have the same options. They either stay in the Mid-East, spread into Eurasia, or head back to Africa. But because the Neaderthal absorption event took place in the Mid-East, I’m thinking disproportionately more hybrids would remain there relative to humans. The likelihood of getting Neanderthal genes seems like it should increase the closer you live to the area where the interbreeding took place. Just like any mutation.
I dunno, this seems more likely to me than the explanation that one block of humans came out of Africa and rather uniformily absorbed the Neanderthals, creating in effect a new breed of people who then split off into Caucasians, polynesians, etc. But I’m not an anthropologist so this reasoning of mine could very well be completely off base.
ywtf: I don’t think you have things wrong. Keep in mind that the study found 2 places where hybridization seems to have taken place-- In the Middle East and in South Asia. I don’[t think it’s unreasonable to expect there to be a gradient in the geographic distribution of remnant Neanderthal DNA. The populations of Northeast Asia and Europe are relatively closely related, as compared to the Austronesian populations. And those Austronesian populations may have hybridized with even more primitive populations than Neanderthals-- ie, remnant Erectus populations in Southeast Asia.
