I know that there are older theories that predict the same thing thing. They are based on odd models that were what we would call racist today. However, that doesn’t mean that something similar is completely wrong either. The Out of Africa hypothesis is also wrong at least in some sense. The OoA hypothesis is still largely correct but it never accounted for genetic contributions from the other human species that existed at the same time. It has to be revised into a more complex model and that is what is being done right now now among evolutionary anthropologists and biologists based on real scientific findings.
I am still not buying the idea that semi-extreme morphological changes happened in multiple human groups in just a few tens of thousands of years without an outside set of genes to select from. I admit that it does happen in some species like dogs that undergo intentional selective breeding to produce very specific traits in much less time than that but I am not aware of any effects that large that have ever occured in wild populations in that short of time.
I am not wedded to this idea. I think the whole thing is fascinating. The near iron-clad proof that modern humans from non sub-saharan Africa have DNA contributions from at least two extinct other human species is mind-blowing enough. The fact that there were true hobbit people around in the not so distant past is also incredible. You might as well deliver a Bigfoot and a Leprechaun to my door tonight for me to be equally surprised (please note that I don’t believe in either of those but something remotely similar did at one time).
I expect a whole lot more about the true understandings of human origins in the not so distant future based on these lines of research.
While I find the interbreeding data to be fascinating, it didn’t surprise me one bit. And I wouldn’t consider the MRH to be racist. It was just a hypothesis based on fossils, not any comment about relative superiority or inferiority of the classical “races”.
Re: Out of Africa theory, the San people exhibit facial features that are a mix of negroid, mongoloid, and caucasoid. They aren’t a mix of these races, rather it is likely that today’s races stemmed from ancient peoples like the San.
Absolutely true. They are among the most likely founders of most of the modern European and Asian lines. However, my point still stands. I don’t see how you take a tribe of migrating Sans ancestors and turn them into Swedes, Irish, Japanese and Australian aborigines (just a few examples) with just a few tens of thousand of years to work with. It doesn’t pass the smell test and would require proof that we do not have.
I think that is the piece that always irritated people about the original Out of Africa hypothesis me included. It just doesn’t work through any known science. There has to be major pieces missing.
It most certainly does work through “known science”. It is, in fact, the consensus among actual scientist who study this. I’m not aware of many scientist who are “irritated” by it. If you mean non-scientists, then I’m not surprised. That’s often the case with science.
How many mutations do you think it takes to go from dark skin to light? I think you’re hung up on the superficial difference of skin color.
Of course it does. Major changes can take place especially in small populations, due to either strong selection or founder effects. Nothing about the differentiation of human populations is inconsistent with what is known about genetics.
Also, those differences seem more dramatic because we are hyper-sensitive to slight variations in other people. It’s like if you don’t listen to a particular type of music, it all sounds the same, but if you listen to it, the variation is remarkable. Were I a rat, perhaps all rattus rattus would look as varied and distinct to me as people look now, and were I an alien species looking down on earth, perhaps I would wonder how we all tell each other apart, as similar as we all seem.
If there was a fairly strong evolutionary advantage to lighter skin (as in Vitamin D absorption in cloudy northern latitudes?) then it seems like it wouldn’t take all that many generations to produce an effect. What about Darwin’s moths?
As others have noted, the species concept is quite flexible and there are often no rigorous delineations between associated species (and the converse is true as well; some species defined by presumed monophyletic association based upon characteristics are later found to be the result of evolution converging on similar solutions). It is unsurprising that there are several distinct populations of of genus Homo, and indeed, the big surprise is that there are not more (as there may well be) given how rapidly Homo sapiens has expanded to become a keystone species. What we can observe is that what we classically observe as H. sapiens has become the dominant part of the shared genome while other human species have been absorbed or died out, indicating that for whatever reason, the humans emerging from Africa around sixty thousand years ago were more adaptable to conditions and better able to compete with other species. Whether this was due to innate intellectual capability, some degree of cultural or technical prowess (language, tool-making skills), or that they carried infections to which they had acquired immunity but populations native to Eurasia did not (similarly to how the Europeans ‘conquered’ the Americas by bringing their plagues of smallpox and influenza to devastate native populations) is unclear.
As to what it “means”, science, and in particular population genetics, can only tell us in quantitative sense, e.g. the frequency of which different alleles occur in populations which are identified to originate from different areas. This is most useful in terms of propensity toward genetic illnesses or susceptibility to diseases and chronic illnesses. In terms of intellectual and psychosocial potential, there is such a large contribution of environmental and social effects on development and the interplay between various genes that except in the case of pathological conditions (e.g. psychopathy, affective disorders) it is unlikely that clear distinctions can be made between populations.
The thing is, although you may think that the differences in morphology between populations are “semi-extreme”, in fact nearly all variation in human phenotypes is a matter of regulation of existing genes rather than a novel addition (via mutation or introduced genes) to the genome. Ever human on the planet, except for albinos, have the innate ability to produce melanin (the pigments that control coloration of the skin, hair, and iris). For (most) people of Eurasian descent, the production of melanin is sharply reduced, but it is noteworthy that other populations descending from the same wave of migration out of Africa still produce enough melanin to have dark skin, and indeed, some populations (in modern India, Polynesia, Australia and Melanesia) have darker skin than some native populations in Sub-Saharan Africa. There are four identified genes associated with the light skin color in Europeans which regulate and limit the production of melanocytes; that these genes would ‘rapidly’ (in the span of 20-30 kyr) spread between the relatively isolated populations of Europe is unsurprising given the archeological history of regular migrations between regions.
The original hypothesis–that a single wave of populations spread out from Africa over a fairly narrow time–has certainly been modified by population genetics to indicate that migrations have occurred fairly consistently since the rise of modern humans, and were likely occurring with frequency prior to the rise of what we would regard as anatomically modern humans. But that human populations originated from Africa, expanded into the Eurasian supercontinent, developed ethnic-specific morphotypes over a series of eons, and then intermixed due to commerce and conquest, is factually undeniable, and indeed, I expect that we will find increasing evidence of it happening as an almost continuous process since the rise of H. erectus with many variations (be they defined as species or subspecies) developing, intermingling, and being absorbed.
Nor is it questionable that the breadth of genetic variation of the populations from Sub-Saharan Africa vastly exceeds the entire rest of H. sapiens populations combined together, such that the evolutionary benefit of any single or small set of genes (except in terms of susceptibility to pathogens or genetic disorders) is likely small to negligible in the overall scheme of human variation.
The question of recovery (in genetic terms) isn’t related to the quantity of organisms but the diversity between them. A genetically diverse species is robust against a wide range of pathogens and moderate changes to the environment, simply because they have more ways to adapt. A species that is not diverse–that has a narrow range of genetic variation–is more prone to plagues and other effects which may prey on any particular genetic ‘loophole’ or weakness. Our lack of immunity to various Type A influenzas (compared to the species which often act as carriers but experience very low to negligible mortality) and viral hemorrhagic fever result in high rates of mortality (in extreme cases 50%) across all human populations. In essence, modern humans (regardless of race, ethnicity, or differences in appearance) are essentially in the same category as highly bred racehorses or Great Danes; carrying a narrow range of genetic variability, a number of developmental features of questionable evolutionary utility, and prone to a wide range of chronic illnesses and conditions which natural selection has not had time to fully cull from the population.
Last I heard the evidence was leaning towards Sapiens red hair and Neanderthal red hair being caused by different genes. If that is indeed the case the answer is “no” and red hair evolved independently at least twice in the Homo genus. (And at least three times among the primates, Orangutans being gingers.)
However, I am not an authority in these matters and further evidence may have come to light.
That’s one part of the theory that I have trouble grasping. If there was limited interbreeding (once every 30 years is a figure I’ve seen), wouldn’t there have been a lot of homo sapiens, maybe even whole groups of them, who never produced any hybrid progeny and would carry completely non-Neanderthal DNA to whatever part of the world they migrated?
Within the last year, there was a hypothesis put forward that the Neanderthal genes we have aren’t the result of interbreeding but are remnants of the common ancestor we had with Neanderthal. In light of my question above, that made sense to me, but it was soon discredited, so that still leaves me with the question (which I know is borne of my ignorance of the topic and not the theory itself, but my mind won’t rest till my ignorance is fought).
But there has been so much interbreeding within populations of Modern Humans, that it gets swamped out. And keep in mind that we’re talking statistics here. If the Average European has 2-3% Neanderthal DNA, there is going to be lots of variation around that point. And when you get to populations in Africa and Australia, for instance, then you find little to no Neanderthal DNA.
Stranger on a Train hit the nail on the head. A lot of the modern variation may be accounted for by regulatory changes to pre-existing genes. It is much easier to up or down regulate the production of a protein/enzyme than it is to start with nothing an evolve it anew.
And keep in mind that a lot of change can be accomplished in a short time by changes to a relatively small number of genes. About half the size difference in small dog breeds can be accounted for by only six genes. Those changes, through selective breeding, have largely occurred in the last thousand years or less.
Remember that in a small population after a few generations the entire population will share the same ancestors in the original population. It wouldn’t take very many Neanderthals in the ancestral population for a few genes to spread throughout the entire population 10 generations down the line.
This would be especially true of those genes presented some reproductive advantage. One hypothesis is that, as newcomers to the area, we would have benefited from some of the Neanderthal’s natural resistance to the local microbes.
