The presumption of a late appearance of AMH in eastern Asia has been largely prompted by a remarkable yet dubious ‘gap’ between 100 and 40 ka ago lacking any human fossils, specifically between the latest archaic H. sapiens (i.e., Xujiayao, 104–125 ka and Maba, 129–135 ka) and the earliest modern H. sapiens (i.e., Ziyang, 35-40 ka) (data pooled from Wu and Poirier, 1995). In addition, genetic studies of present-day Chinese populations have supported the late appearance of AMH in eastern Asia (e.g., Chu et al., 1998). From this perspective, the AMH fossils from Tianyuan Cave at Zhoukoudian in northern China, dated to 39-42 ka B.P. (Before Present), have been readily accepted as the earliest representatives of modern H. sapiens in China, and the earliest evidence for the influx of African genes into the indigenous population (e.g., Shang et al., 2007; Cartmill and Smith, 2009; Endicott et al., 2009).
However, the credibility of this supposed ~60 ka gap in the hominin fossil record and a late appearance of modern humans in China might have been compromised by the exclusion of a number of hominin fossils claimed to represent AMH from various limestone caves in southern China with more ancient dates, including Liujiang (between 68 and 153 ka, and most probably between 111 and 139 ka, Shen et al., 2002b), Ganqian (94–220 ka, Shen et al., 2002a), Bailiandong (>160 ka, Shen et al., 2001b), and Zhirendong (>100 ka, Liu et al., 2010a) in Guangxi. Based on our work on the sites of H. erectus and of both archaic and modern H. sapiens over the past twenty plus years, we argue that the temporal framework in China has been artificially ‘compressed and gapped,’ meaning that due to limitations in previous dating techniques and practices, the ages of Chinese hominin fossils have been significantly postdated (compressed), and that a temporal gap between archaic H. sapiens and AMH has been artificially created (gapped). To this scenario of the possible early presence of modern humans in China, here we report evidence from Huanglong Cave, a recently discovered Late Pleistocene hominin fossil- and stone artifact-bearing site, and discuss its impact on the mode of recent human evolution in eastern Asia.I guess a lot depends on whether these teeth are accepted as belonging to AMH; if this holds, the early range of AMH must need to be extended even further east.
Such early dates are often seen as conflicting with the molecular clock (e.g., West and East Eurasians don't appear to have diverged ~100 thousand years ago no matter what assumptions about mutation rate one makes). But, we should not forget that divergence times can be suppressed either due to (i) admixture between the divergent populations, or (ii) due to an expansion of a highly successful population.
Journal of Human Evolution doi:10.1016/j.jhevol.2013.05.002
Mass spectrometric U-series dating of Huanglong Cave in Hubei Province, central China: Evidence for early presence of modern humans in eastern Asia
Guanjun Shen et al.
Most researchers believe that anatomically modern humans (AMH) first appeared in Africa 160-190 ka ago, and would not have reached eastern Asia until ∼50 ka ago. However, the credibility of these scenarios might have been compromised by a largely inaccurate and compressed chronological framework previously established for hominin fossils found in China. Recently there has been a growing body of evidence indicating the possible presence of AMH in eastern Asia ca. 100 ka ago or even earlier. Here we report high-precision mass spectrometric U-series dating of intercalated flowstone samples from Huanglong Cave, a recently discovered Late Pleistocene hominin site in northern Hubei Province, central China. Systematic excavations there have led to the in situ discovery of seven hominin teeth and dozens of stone and bone artifacts. The U-series dates on localized thin flowstone formations bracket the hominin specimens between 81 and 101 ka, currently the most narrow time span for all AMH beyond 45 ka in China, if the assignment of the hominin teeth to modern Homo sapiens holds. Alternatively this study provides further evidence for the early presence of an AMH morphology in China, through either independent evolution of local archaic populations or their assimilation with incoming AMH. Along with recent dating results for hominin samples from Homo erectus to AMH, a new extended and continuous timeline for Chinese hominin fossils is taking shape, which warrants a reconstruction of human evolution, especially the origins of modern humans in eastern Asia.
Link
32 comments:
I was sure something like this was coming, but it's always sad when you see the reason for errors like this is simply ignoring any "wrong" data. Should be easy to tell if they are modern human teeth.
The material quoted from the paper certainly does alleviate some concerns about the veracity of its results that I'd had trying to consider its conclusions based on the abstract and mass media coverage.
But, until there are more results that can be fit to the gap both geographically (i.e. between India and China) and temporally, I'm still inclined to be skeptical, although no longer dismissive.
Hmm. I am a bit surprised we are even talking about anatomically modern humans in this way at this time. As if we still beleived in the purity of AMHs. As if admixture with Denisovans and neanderthals had never happened.
Improve the dating, fine. But the perspective should now be that there really is no true difference between Homo sapiens and Homo sapiens sapiens. "Homo sapiens" as we know it descends from "Homo sapiens sapiens". In every case that I know of. From Cromagnon to the robust folk of ancient australia.
Just to be clear, the "gap" from 100 kya and 40 kya is in Asia only, right?
Question now is whether the Out of Africa scenario is threatened by this and whether this early appearance of AMH in Asia was suppressed by the dominant political paradigm in america--that being multiculturism and its associated memes.
More specifically, the "gap" from 100 kya to 40 kya was in SE Asia and East Asia, but not in South Asia or West Asia or SW Asia. (Although there is now a ca. 60 kya find in Vietnam).
It is not just the duration but the immense geographic extent of the "gap" that makes it problematic. But, if the "gap" is as this article suggests a methodological artifact rather than real, and the geographic extent of the gap is just a function of decolonization and geopolitics diverting resources from archaeology in the region, then the gap has a decent chance of being filled in the medium term future.
A few years ago, they also talked about a "gap" from 75kya to 50kya in SW Asia (basically coinciding with the MIS 4 period), but new Arabian interior digs are dispelling that impression.
Europe and Central Asia, in contrast, have Neanderthal presence all of the way up to and overlapping briefly with AMH (Cro-Magnon) arrival, and there is (of course) no "gap" in Africa, where AMHs have been continually present since they first evolved.
Of course, AMHs are the first hominin species on the far side of the Wallace line past Flores, and are the first hominin species in the Americas.
Annie Mouse,
I have to agree and am constantly taken aback on an almost daily basis by how so much of the Anthropological world continues to operate as if the confirmation of the Neandertal contribution to the modern genome and the discovery of the Denisovan hominid have not occurred. I had thought that both discoveries would be the final nails in the coffin of the overly simplistic Out of Africa theory but most OoA proponents that I discuss both discoveries with routinely dismiss them both out of hand as being irrelevant or engage in acrobatics to claim that both discoveries are in fact supportive of OoA.
Otzi the iceman had a lot more neanderthal DNA than modern europeans, too. A lot of the supposed out of africa effect has really been from asia, and from in much more recent times.
They used to have a saying in England "long barrows long skulls, short barrows short skulls". Basically the inhabitants of the british isles were nearly completely replaced by invaders around 5800 bc. They went from farmers and megalith builders backwards to pastoral farmers. However this was rejected as a racist theory since it didn't shed a good light on the current inhabitants, the ancient invaders.
Longs skulls, by the way, are a sign of higher neanderthal heritage. When you have people being replaced by genoicide or by large immigration waves then your results get wildly skewed.
I don't think it's bad to talk about different types of ancient human because you have to call them something, but you have to recognize that things looking a certain way in this point in time can have a lot of interpretations and work more with the facts and less with your political agenda as has been the case in recent times in europe and always been the case in east asia.
As for "modern" humans coming from africa I think they are simply a blend of peking man and neanderthals. If you take a neanderthal face and an asianlike face and blend them together you get something that looks very similar in shape to modern europeans and middle easterners and south africans.
Homo erectus sebida look exactly like chimps, they have curled fingers even though more gracile but much older hands with straight fingers have been found on incomplete skeletons. They also seem to have matured at 8 years old like a chimp and have brains the size of a chimp.
Peking man on the other hand has brain comparable to moder brain and neanderthal even larger.
There's just no fossil record of "modern" humans in africa until they just show up full formed if you take out sebida (which we should). So not only are we very sure at this point of multiregionalism but with the evidence that's come out recently it seems like there was no out of africa at all of any kind at any point of time except maybe 1.8 million years ago.
Grognard
The phylogeny of the Y and mitochondrial trees clearly shows Out-of-Africa. It is just a matter of when, and how much admixture along the way.
Hard to explain away how A00 and other root groups are all in Africa otherwise.
I am of the opinion that the hoopla about the Sediba hominids is much ado about nothing and they are representative of nothing more than a late surviving Australopithecine population whose primitive features far outweigh any overlap with more modern looking (and much earlier) Homo.
"As if admixture with Denisovans and neanderthals had never happened".
Yes. Many, often surprising individuals, still talk about a sudden arrival of modern humans, a new species. That has never made sense to me.
"divergence times can be suppressed either due to (i) admixture between the divergent populations, or (ii) due to an expansion of a highly successful population"
And I would guess that both have been extremely common as humans have moved backwards and forwards around the world.
"the ages of Chinese hominin fossils have been significantly postdated (compressed), and that a temporal gap between archaic H. sapiens and AMH has been artificially created (gapped)".
This study supports the possibility that the EDAR370A mutation did not occur in a 'modern human', but introgressed from an 'Archaic'.
Annie Mouse,
I do not think that anyone here is trying to say that a migration out of Africa by the human species did not occur. The difference and the devil are in the details. In my opinion the picture painted by the Y and Mt haplogroup information is anything but clear at this point. I estimate that it may take at least another decade of research before a clear picture begins to coalesce. What the research to date seems to be showing us at this point is that the process is far more complex than the simplistic OoA model predicted, primarily by laying to rest the claim that no admixture between AMH and preceding populations occurred. I am of the same opinion as Grognard that the only OoA that can be definitively demonstrated to have occurred was the one that occurred 1.8-1.9 mya. I think that the haplogroup information is also confirming the species-wide and inter-population gene flow predicted by Multi-Regionalism.
"
The phylogeny of the Y and mitochondrial trees clearly shows Out-of-Africa. It is just a matter of when, and how much admixture along the way.
Hard to explain away how A00 and other root groups are all in Africa otherwise."
That's exactly what you'd expect to see in small isolated groups. You do NOT expect to see that in a place where something evolved.
Any group that interbreeds is going to blend together and move towards having the same values over time. So if they all did evolve somewhere in africa you would EXPECT to see all africa overwhelmed by a single group that expanded at some point. Especially if you believe in a recent out of africa that would require a massive expansion.
For REAL expansions that's exactly wat we get. Arabs are very homogenous. Han Chinese are even more numerous and even more homogenous!
And black africans have expanded recently and have become more homogenous aside from these most isolated areas. So that means it was even more heterogenous until the last few hundred years. Which doesn't make any sense at all for a recent out of africa hypothesis.
What africa really looks like is a place that's had successive waves of immigration. The most acient groups are also in the remotest and least hospitable parts as well. Nothing evolved there!
That much we can be sure of. We also have, in cameroon, paleolithic fossil skulls that are linked to north africa and middle east DNA, ie not the people who are currently there at all.
We also have big pockets of a subtype of r1b Y-DNA in cameroon as well, right by this most ancient DNA.
The DNA evidence for out of africa is really kind of meaningless.
There's not been any recent out of africa, and probably there's never been any mass migration out of africa at all. The human-chimp ancestor candidates are all outside of africa as well. So maybe heidelbergensis came from africa, that's about it, and that's not certain either.
I am of the same opinion as Grognard that the only OoA that can be definitively demonstrated to have occurred was the one that occurred 1.8-1.9 mya. I think that the haplogroup information is also confirming the species-wide and inter-population gene flow predicted by Multi-Regionalism.
CleverPrimate,
Are you suggesting that the uniparental DNA time estimates are wrong by a factor of ~20, and that humans and chimps diverged 160 million years ago?
I should claryify what I mean by expansion and homogenousness in regard to OoA.
In any out of africa theory paper they talk about a series of founder effects. Basically one little group escaped africa, then that group became middle easterns, then a little group escaped middle east and became Indians. Then a group broke off of them and became east asians and so on.
But if that's the case and it's a series of founder effects then there shouldn't be a bunch of everything in africa but only whatever the oldest is and variations on it. Since there's a bit of everything and the oldest stuff is only in a few pockets where the population is isolated (which we also see outside africa) it means nothing at all and looks the opposite of what we expect.
If that is where humans with modern behavior had the biggest populations then that would also be where things like lions and megafauna predators went extinct first, not eurasia.
eurologist,
No, that is not what I am saying. What I am saying is that the picture painted by the DNA information is still unclear. Please correct me if I am wrong but I believe that time estimates are still being hotly debated, primarily due to differences in the mutation rate used. I do not believe that I made any mention of the human-chimp TRMCA but by no means do I believe that it was 160 mya. I do believe that it may be somewhat earlier than the commonly accepted date.
Time estimates are meaningless as they assume that mutation is random, but we already know it's not. There are periods of great change and they can be followed by indefinite lack of change.
I'd put chimp-human ancestor at more like 30-50 million years...and that's where actual fossils exist that could be likely candidates. Humans don't have the same number of chromosomes, even.
Insects never become arachnids or vice versa, they were always insects or arachnids. The point is, when there's room for great expansion you can change a lot but most likely all the upright walkers came from the same ancestor and it only evolved once. There was no back and forth between knuckledragger and upright walker.
You can't really look at number of mutations and come up with any meaningful data, because it has big assumptions behind it which are flawed. That's why you get these ridiculous statements like 8 million years +- 250k and someone else gets 3 million years +- 1 million years. It's just not valid math.
Chimp is perfectly evolved for its environment and it's stayed right there. If homo erectus sebida was a human ancestor it means that something just like a chimp because a human and then chimps came from somewhere else to fill the former human niche but maybe they were chimps all along and we have yet to find a smoking gun (actually we kind of have it already just not in africa).
Please pardon my typo. I meant to use “TMRCA”.
"In any out of africa theory paper they talk about a series of founder effects. Basically one little group escaped africa, then that group became middle easterns, then a little group escaped middle east and became Indians. Then a group broke off of them and became east asians and so on".
I agree with you that that scenario seems unlikely. Annie has been suggesting that the original small group interbred with resident groups as it expanded, and I agree with that.
"What I am saying is that the picture painted by the DNA information is still unclear. Please correct me if I am wrong but I believe that time estimates are still being hotly debated, primarily due to differences in the mutation rate used".
I think it unlikely that various haplogroups form at a particular rate. However I agree with Eurologist that it is extremely unlikely that the uniparental DNA time estimates are wrong by a factor of ~20. The haplogroup data surely demonstrate 'something'. My guess is that basically Y-DNA represents technological expansion and mt-DNA represents cultural expansion, but we need to wait and see.
"Any group that interbreeds is going to blend together and move towards having the same values over time. So if they all did evolve somewhere in africa you would EXPECT to see all africa overwhelmed by a single group that expanded at some point. Especially if you believe in a recent out of africa that would require a massive expansion".
As I explained above I think it very unlikely that any OoA represented by haplogroups does not represent a massive expansion. The survival in Africa of haplogroups such as A00 are no surprise to me but their survival does show an expansion from Africa at some time after the original Homo erectus/Australopithecus exit.
I think OoA at some point is very likely but not the only possibility and can't have happened as quickly or as a series of founder effects where the observed differences in modern humans are just founder effects.
“I think it unlikely that various haplogroups form at a particular rate. However I agree with Eurologist that it is extremely unlikely that the uniparental DNA time estimates are wrong by a factor of ~20. The haplogroup data surely demonstrate 'something.”
I agree that the origins of haplogroups are still poorly understood. I also agree that the haplogroup data is showing us something, but what I think remains unclear is just exactly what that something is. I never made any attempt to quantify the DNA time estimates or by what factor they may be miscalculated, I merely questioned their certainty. Nor did I make any attempt to date the human/chimp split.
“I agree with you that that scenario seems unlikely is. Annie has been suggesting that the original small group interbred with resident groups as it expanded, and I agree with that.”
This is the very point I was attempting to make. There were “resident” populations and those populations interbred with and produced fertile offspring with AMH as they were encountered, producing the regionally variable populations we observe today. The resident populations were not footnotes but integral to the process. This is the one fact that the DNA material is clearest on, that there was indeed admixture with resident “relic” populations. Due to the factors of time and population size the DNA contribution of the relic populations has mostly been washed out of the genome but still remains at detectable levels in all but sub-Saharan populations.
In any out of africa theory paper they talk about a series of founder effects. Basically one little group escaped africa, then that group became middle easterns, then a little group escaped middle east and became Indians. Then a group broke off of them and became east asians and so on.
Grognard,
I have actually never seen that promulgated in a scientific paper. Serious theories, based on uniparental and autosomal DNA, suggest that most modern ooA humans trace their origin to S and SE Asia, with minor Neanderthal admixture (most of it early on) and some "Denisovan" admixture (perhaps heidelbergensis) some place to a small group that eventually ended up in the far SE.
That is, during dry times following times suitable for ooA expansion, very, very few (if any) humans survived in the arid transition regions, and some of those regions got re-occupied by Neanderthals around 80,000 - 60,000 ya. That is why regions west of India/ Pakistan got re-populated by humans from that region ~ 50,000 - 45,000 ya (and ~35,000 - 30,000 ya from South Siberia / the Altai).
After that some additional admixture to and From Africa, and more admixture from Siberia to Europe, and in neolithic times from West Asia to Europe. And, of course, lots of movement in Asia, as well (rice agriculturalists expansion, Polynesian expansion, etc.).
http://johnhawks.net/weblog/reviews/genomics/variation/serial-founder-effects-2008.html
Until recently I don't think any OoA paper included any multiregionalism features.
And if it's out of africa it must have come from africa before india.
Multiregionalism says differences in people come mainly from selection, OoA says they come mainly from founder effects.
Even if it's entirely multiregional for 600k+ years that doesn't mean that there is no exchange of genes. It just takes one individual and if it's a gene that gets selected on strongly it will become fixed. Also I'd not be surprised if people for the last million years have had intelligence comparable to today so there may not have been that much of big differences to overcome. OoA relies on some giant fluke mutation followed by lack of any real evolution after that to work. You could say evolution has been redefined by OoA because now this genetic drift nonsense is part of the definition.
Grognard wrote:
> What africa really looks like
> is a place that's had
> successive waves of immigration.
> The most acient groups are
> also in the remotest and
> least hospitable parts as well.
Not only does the DNA look like this for Africa, but also the linguistic pattern across Africa (particularly taking note of such language groups as Bantu compared to others) clearly shows a pattern of successive waves of expansion/invasion. Later languages expand and invaded over older cultures, pushing the older cultures to more remote locations if they wished to survive. This matches the wave invasion description given by Grognard.
First off I'd agree with Eurologist's summary. And CleverPrimates commnet:
"There were 'resident' populations and those populations interbred with and produced fertile offspring with AMH as they were encountered, producing the regionally variable populations we observe today. The resident populations were not footnotes but integral to the process".
Research seems to be taking us back towards some sort of 'regional continuity' theory. But I note no-one has apologised to Milford Wolpoff or Alan Thorne for the flack they received when they first postulated the theory.
"I'd put chimp-human ancestor at more like 30-50 million years...and that's where actual fossils exist that could be likely candidates. Humans don't have the same number of chromosomes, even".
No-one but you would place the split so ancient. The main argument is between 6 million and 10 million. Sahelanthropus tchadensis looks pretty close to both human and chimp but is only 7 million years old.
http://en.wikipedia.org/wiki/Sahelanthropus
Quote:
"Sahelanthropus may represent a common ancestor of humans and chimpanzees; no consensus has been reached yet by the scientific community. The original placement of this species as a human ancestor but not a chimpanzee ancestor would complicate the picture of human phylogeny".
Secondly, chromosome number is not relevany when it comes to hybrid forming capacity. Domestic and Przewalski's horse have different chromosome numbers but are fully interfertile.
http://en.wikipedia.org/wiki/Przewalski's_horse
Quote:
"The karyotype of the domestic horse differs from that of Przewalski’s horse by an extra chromosome pair either because of the fission of domestic horse chromosome 5 in Przewalski’s horse or fusion of Przewalski’s horse chromosomes 23 and 24 in the domestic horse. In comparison, the chromosomal differences between domestic horses and zebras include numerous translocations, fusions, and inversions. Przewalski’s horse is known to have the highest diploid chromosome number among all equine species. Przewalski’s horse can interbreed with the domestic horse and produce fertile offspring (65 chromosomes)".
Every skull found is mega important to some people, but the truth is we find new species of primate almost every single year even today.
Ask yourself why did the A00 suddenly stop evolving in some people. If humanity were evolving there dramatically then it makes no sense for this to just stop one day.
With the comparisons of the molecular clock at 20x rate for some compared to others...well, that's exactly what happened. Some have stayed almost the same, while others have dramatically changed.
That seems to be exactly what happened with chimps, they have stayed in the same niche with nowhere else they can go to and stayed almost exactly the same. Clearly the homo erectus sebida is simply chimp ancestors, who lived in current chimp territory, and by their tooth calculus ate exactly what modern chimps do. It especially falls apart when they have found an older but more humanlike complete hand. Whoops!
The whole mistake is they assume evolution comes at a certain rate but it comes due to selection and opportunity for selection, which chimps don't have because humans and their ancestors were in the way.
I also believe humans and apes are more closely related than humans and chimps. And again, before sampling an incredibly minute part of the human and chimp genomes and declaring them 99.7% the same (on this narrow band where all animals are alike) this was the standard theory. Because insects don't become arachnids willy-nilly, and just the same monkeys don't shift back and forth between upright walking and knuckledragging. All the knuckledraggers and walkers split one time and that was that, as it happens with every large change. Worms won't just decide to grow a spine one day, it only happened once and everything with a spine evolved from that same little fish.
Often papers point to the diversity of a specific Y-DNA or mitochondria that's ancient in africa as well. What's this? According to fantasyland where there is no selection, again we get some mythical random mutation rate but it doesn't work like that. Drift like this is due to LACK of selection pressure, real evolution comes from expansions followed by bottlenecks.
You can interbreed carp with goldfish too but they are a lot more separated than most minnows and big changes like that take time to occur.
I also know quite well what the typical believed date is for human chimp divergence, but 100% of this is based on molecular clock nonsense. The REAL candiates from fossil record, unlike your random skull, are 30-50 million years old.
Homo erectus sebida and lucy have been all but totally disproven. Every old skull or bone at first is a stunning breakthrough but the more we do find the more clear it is how little has been found yet. Right now there's a huge upsurge in archaeology in China, hundreds of tons of dinosaur and other bones coming to light. They've always been there and they knew about many of the sites a long time, but no one has been looking until now.
There's another place in china that had some old bones with prognothicated neanderthal like chins, but of people who existed maybe 20k years ago. I saw that long before the denisova stuff came out and didn't think to bookmark it unfortunately; they didn't even seem to really care (and much info in china about human origins is repressed for political reasons, just as political reasons seem to drive people more and more in the west).
"Ask yourself why did the A00 suddenly stop evolving in some people. If humanity were evolving there dramatically then it makes no sense for this to just stop one day".
Are you sure it stopped evolving? According to ISOGG A00 has had at least fifty mutations since it split from the 'mainstream':
http://www.isogg.org/tree/ISOGG_HapgrpA.html
"All the knuckledraggers and walkers split one time and that was that, as it happens with every large change. Worms won't just decide to grow a spine one day, it only happened once and everything with a spine evolved from that same little fish".
You're proposing something completely impossible here. If just one worm suddenly grew a spine and became a fish it would not leave any descendants. It would be unable to breed with any other worms. Mutations have to spread through pre-existing populations. That is how evolution works.
"Homo erectus sebida and lucy have been all but totally disproven".
On what grounds do you claim that to be so?
"Are you sure it stopped evolving? According to ISOGG A00 has had at least fifty mutations since it split from the 'mainstream':
http://www.isogg.org/tree/ISOGG_HapgrpA.html"
This is what we call drift. Drift is not selection. As I said already, if it were selection then it would be MORE the same, not less.
There's a ton of selective sweeps going on right now, but this gene in this location is not under selection pressure.
"You're proposing something completely impossible here. If just one worm suddenly grew a spine and became a fish it would not leave any descendants. It would be unable to breed with any other worms. Mutations have to spread through pre-existing populations. That is how evolution works. "
Nice and insulting response, thank. But maybe you misunderstand me. Obviously I did not literally mean magic created a spine in a worm in a single day; yet a worm will never, ever evolve a spine so long as more sophisticated spined animals are around as competition.
The thinking that evolution is not about selection, which from your comments you believe in as well, is the magic. That is what it means to magically start moving in a direction. Or magically have some rate of change.
No, selection is what evolution is. Selection and purification. Random changes like you see in the A00 are just that. Random stuff that has had no real effect. The key is that not only do they randomly occur they randomly fade away as well. Back to the comments a few posts back, you don't randomly move IN A DIRECTION. You randomly scatter but basically stay the same. When there is strong selection advantage then you get a selective sweep and that is obviously not happening.
And in those individuals has not happened in their ancestors for hundreds of thousands of years or even millions for all we know.
Not on those genes, anyway. And if they are living a lifestyle similar to how humans lived that long ago then really there's no reason there should be selection on it.
Back to the worm example, a spine evolved one time in history. It won't ever evolve again, because there is competition from creatures who have been in the spine business for much much longer than current invertebrates. It's a case of "you can't get there from here". There's no advantage to a spine because the spine niches it could take advantage of are filled and it could not evolve one without making it temporarily less effective in its current niche. So it's pinned to that niche.
"On what grounds do you claim that to be so? "
Go back and read? Plus try google from there. Sorry but humans didn't evolve from chimpanze ancestors with pinheads in africa when larger brained hominids were already extant.
http://johnhawks.net/weblog/fossils/sediba/malapa-berger-description-2010.html
All right, here we go. Sorry for double post, could not find link.
Basically sebida has smaller brain than more recent proposed human ancestors, and less gracile fingertips.
To me every implication is this is just a protochimp. This could mean we simply haven't found all this evolution that is supposed to be going on in south africa yet but it could also mean that it's simply not happening in south africa. When you have such a striking pattern where your fossils all have steadily larger brains as you move towards asia then it lends weight to the latter.
http://www.nature.com/news/gorilla-joins-the-genome-club-1.10185
http://johnhawks.net/weblog/reviews/chimpanzees/genetics/chimpanzee-y-chromosome-2010.html
Oh, and here we go, read it and weep.
Humans and gorillas more genetically similar than humans and chimps. Another shocker!
Also, chimp Y-DNA no more similar to human DNA than a chicken's. Whoops! Probably have to go back 30-50 million years to get a common ancestor, maybe more if the chicken comparison is any guide.
Now these are pretty obvious blunders. This should not happen. If you look at fossils and believe in natural selection you know dumb hypotheses like that simply CAN'T be true.
But there has been this gigantic attack on the notion of natural selection because it's both misunderstood and sadly they think it will sell the most books to have a lame hollywood feelgood message. But again selection isn't mixing cake batter, everyone will ultimately eventually get all the genes that are catered to their environment if they exist in some other group.
Natural selection is real. Molecular clocks are a joke. Drift isn't evolution.
"Humans and gorillas more genetically similar than humans and chimps. Another shocker!"
I don't understand why you see it as a 'shocker'. Surely it is extremely unlikely that the split between humans, chimps and gorillas was no simple affair. Genes would have flowed between the three groups early in their separation and so we should find a variety of closer genetic connections between the species.
"chimp Y-DNA no more similar to human DNA than a chicken's. Whoops! Probably have to go back 30-50 million years to get a common ancestor, maybe more if the chicken comparison is any guide".
In spite of John Hawks' commnets it is extremely unlikely to be the case. After all in birds it is the females who have the separate sex-defining chromosomes, not the males:
http://en.wikipedia.org/wiki/ZW_sex-determination_system
Quote:
'No genes are shared between the avian ZW and mammal XY chromosomes,[3] and, from a comparison between chicken and human, the Z chromosome appeared similar to the autosomal chromosome 9 in human, rather than X or Y, leading researchers to believe that the ZW and XY sex determination systems do not share an origin, but the sex chromosomes are derived from autosomal chromosomes of the common ancestor".
John Hawks does explain it thus, 'the structure of both human and chimpanzee Y chromosomes has evolved incredibly fast compared to the rest of the genome'.
The shocker part is sarcasm, after all I already told you this would be the case I just didn't know that they had done the gorilla genome yet. So this means everything you said about a common ancestor at 7 million years is nonsense, they don't even have the correct guess for closest living ancestor.
And that was yet another case of coming up with a convenient number to fit the "facts" at hand, ie the skull you mentioned which I highly doubt is a human ancestor at all.
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