According to the late Harvard University biologist Ernst W. Mayr, the greatest evolutionary theorist since Charles Darwin, “species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.”
Reproductive isolation is the key to understanding how new species form, and many types of barriers can divide a population and split it into two different groups: geographic (such as a mountain range, desert, ocean or river), morphological (a change in coloration, body type or reproductive organs), behavioral (a change in breeding season, mating calls or courtship actions), and others. After isolation, if members of the split populations encounter one another and cannot produce viable offspring that can themselves later successfully interbreed and produce viable offspring (hybrids such as mules are infertile), then these two populations constitute two different species.
Let’s say that a species migrates out of Africa into Europe around 400,000 years ago and becomes reproductively isolated from its ancestral population for the next 320,000 years. It evolves distinctive anatomical features and adaptations for the colder climes. Moreover, even after other descendants of the original ancestral population move into Europe around 80,000 years ago, the skeletons from both groups show no obvious signs of blended characteristics. Modern scientists classify the creatures as two different species.
Then, however, genetic analysis reveals that members of these two species interbred and produced viable offspring that populated Europe and spread eastward as far as China and Papua New Guinea. By Mayr’s definition, these two interbreeding populations are not two species after all, but two sibling subspecies of the original African species. A subspecies has a characteristic appearance and geographic range, Mayr explains, yet he adds this significant qualifier: “It is a unit of convenience for the taxonomist, but not a unit of evolution.”
Thus it is—revealing the identity of my example—that we must reclassify Homo neanderthalensis as Homo sapiens neanderthalensis, a subspecies of Homo sapiens. A comprehensive and technically sophisticated study published in the May 7 issue of Science, “A Draft Sequence of the Neandertal Genome,” by Max Planck Institute evolutionary anthropologists Richard E. Green, Svante Pääbo and 54 of their colleagues, demonstrates that “between 1 and 4% of the genomes of people in Eurasia are derived from Neandertals” and that “Neandertals are on average closer to individuals in Eurasia than to individuals in Africa.” In fact, the authors note, “a striking observation is that Neandertals are as closely related to a Chinese and Papuan individual as to a French individual.... Thus, the gene flow between Neandertals and modern humans that we detect most likely occurred before the divergence of Europeans, East Asians, and Papuans.” In other words, our anatomically hirsute cousins are actually our genetic brothers.
This modified Out of Africa theory holds that around 400,000 years ago a population of hominids migrated northward through the Middle East and into Europe and parts of western Asia. Between 80,000 and 50,000 years ago another population from the ancestral continent journeyed a similar route into the Eurasian landmass, and there the two populations met and mated. We are their descendants. The Neandertal species did not go extinct, because it was never a separate species; instead population pockets of Neandertals died out around 30,000 years ago, whereas other Neandertal populations survived through interbreeding with their modern human brothers and sisters, who live on to this day.
I always suspected that Neandertals and anatomically modern humans interbred, based on a simple observation: humans are the most sexual of all the primates, willing and able to do it just about anywhere, anytime, with anyone (and even with other species if the Kinsey report is to be believed in its findings about farmhands and their animal charges). Given the viable hybrid offspring that the most diverse members of our species have produced as a result of cultural conjoinings through both ancient migrations and modern travel, one has to suspect that close encounters of the corporeal kind occurred not infrequently in those dark and lonely cave nights over the course of those long-gone millennia.
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29 Comments
Add Comment"humans are the most sexual of all the primates"
Reply | Report Abuse | Link to thisWhat about bonobos?
Do bonobos have sex with non-bonobos?
Reply | Report Abuse | Link to thisI think we still "win"?
It seems quite possible that the demands of interactions between (early) modern humans and neanderthals could have contributed to the development of language and artistic expression in modern humans, presuming they were not genetic contributions of neanderthals alone...
Reply | Report Abuse | Link to thisIf modern human males carry the Y chromosome from a man in Africa 60,000 years ago, does this mean that cross breading was a one way trip (African male, Neanderthal female)?
Reply | Report Abuse | Link to thisThe Neanderthals is a group that first developed in ante-neanderthals 500,000 years ago from Homo erectus (Lumley and Lum�ey, 1971). Its craniofacial morphological characters are unique -expansion of the brain and particular revolution of the face with the flattening of the skull base- and clearly differentiate a stage of human evolution called Homo sapiens neandertatensis. This was defined by Mayr in 1974.
Reply | Report Abuse | Link to thisI've followed the Neanderthal/Modern Human debate for the past 15 years and it is great to finally get some proof that Neanderthals are a part of us. I was constantly disappointed after reacding and watching information about Neanderthals becomming extinct. I have always hypothesized that we had to be Neanderthal to some degree. They were just too sturdy and intelligent to have become extinct by way of climate and or (other) human species. Besides, I've always joked by telling people that I eat so much because I'm part Neanderthal (I need some excuse). Thanks Svante Paabo.
Reply | Report Abuse | Link to thisPatrick Tomberlain
Biology Teacher
Longview, TX
I'm a little confused about the numbers. Supposedly we share 96 to 98 % of our genetic material with chimps. Now we hear that 1 to 4 % of our genetic material derives from Neandertals, which at least belong to the same genus if not the same species. Do we add the 1 to 4 % to the 96 to 98% we share with chimps, getting maybe 97 to 100% shared genetic material? Or do we take the 1 to 4 % to be a percentage of the 2 to 4 % that we don't share with chimps? Or are we mixing apples and oranges?
Reply | Report Abuse | Link to this4% of genetic material shared with Neandertals... I don't think it's a proof for not believing in Neandertals' extinction. On the contrary.
Reply | Report Abuse | Link to thisYou may find some interesting pros for the extinction theory in a book that virtually has nothing to do with evolutionary anthropology: Born to Run, C. McDougall.
I don't mean to be silly about this, but some modern, intelligent and successful people have facial features that look, to me, like the drawings made by paleoanthropologists of the Neandertals. There is more variation in the human body (height, weight, posture, facial features) than in many other species, and the experience of separation followed by interbreeding might explain that.
Reply | Report Abuse | Link to thisI, too, know several Neanderthal-esque people
Reply | Report Abuse | Link to thisI never believed for a minute they had gone extinct.
"After isolation, if members of the split populations encounter one another and cannot produce viable offspring that can themselves later successfully interbreed and produce viable offspring (hybrids such as mules are infertile), then these two populations constitute two different species."
Reply | Report Abuse | Link to thisThis in nonsense, both logically and scientifically. With regards to the first point, Two organisms are of the same species if they can produce viable offspring, does not follow from two organisms are of different species if they cannot produce viable offspring. With regards to the second point, as you well know -- or should know -- there are numerous species with can crossbreed and produce viable offspring. Have you never taken a course in botany? More familiarly, what about all the Canid hybrids? Let me guess -- We dont want to say non-Africans are a hybrid species, so we "must reclassify" the poor old Neanderthal? Just stick to the science. You guys are pathetic.
"After isolation, if members of the split populations encounter one another and cannot produce viable offspring that can themselves later successfully interbreed and produce viable offspring (hybrids such as mules are infertile), then these two populations constitute two different species."
Reply | Report Abuse | Link to thisThis in nonsense, both logically and scientifically. With regards to the first point, “Two organisms are of the same species if they can produce viable offspring,” does not follow from “two organisms are of different species if they cannot produce viable offspring.” With regards to the second point, as you well know -- or should know -- there are numerous species with can crossbreed and produce viable offspring. Have you never taken a course in botany? More familiarly, what about all the Canid hybrids? Let me guess -- We don’t want to say non-Africans are a hybrid species, so we are moving to reclassify the poor old Neanderthal?
To clarify, Mayr had <a href="http://www.pnas.org/content/102/suppl.1/6600.full">two concepts of species</a>: his species as metapopulation lineage and his species as intrinsic reproductively isolated population. There is across the board acceptance of the first definition, but not the second -- last I checked. Under both definitions, organism which cannot potentially produce viable offspring belong to separate species. Only under the second definition do organisms which can produce viable offspring necessarily belonging to the same species. In that sense, dogs, dingos, jackals, and coyote necessarily belong to the same species. And numerous plant species.
Reply | Report Abuse | Link to thisNow, either the species debate was recently resolved -- or the author of this article is making a specious argument for why <a href="http://www.pnas.org/content/96/13/7117.long">Homo neanderthalensis</a> "must be reclassified."
I agree with you "Chuck15". This article seems to be another piece of politically correct garbage. The numbers and architectural findings by other scientists just do not add up to interbreeding of species. Until about six thousand years ago, and still today, in parts of Africa and Australia, mammals are hunter/gathers and other tribal mammals are not allowed to enter each others areas without starting a war, which would lessen tribal populations and one or both tribes would die out.
Reply | Report Abuse | Link to thisAnd look at the people in the Outback of Australia, they are the modern Neandertal and they forbid tribal members to breed outside their area. I'm not saying it doesn't happen, it's just strictly controlled by both species and most time the Neandertal will kill the hybrid offspring if it stays in their area.
Some of our modern humans are are so ashamed of themselves that they think they will feel better pretending they are someone or something else are pathetic. We are not the first human-like species that have lived on this planet and we will not be the last. We are not the smartest and we are not the dumbest human species who has lived here and we will not be the last. Just because we may look like another species or can breed with another species does mean that we came from that species. How do you explain the modern human that does not have any Neandertal DNA in them?
Just because you reword somethings or change a couple of dates does not make what you are saying credible or even true and just because something will work on us and on a rat does mean that we evolved from that rat. Wake up people and pull your politically correct heads out of the sand, take those rose-colored glasses off, and look around you and accept what you see and come to realize that what you see was here before you were and you are not part of it. Believe what your ancestral fathers have told you, "You are not of this world."
Everything in our genome that we share with chimps, Neandertals also shared with chimps, because both our populations diverged from the chimps' line at the same evolutionary fork.
Reply | Report Abuse | Link to thisdinaric people of the balkans have been alleged to be direct neandertal descendents
Reply | Report Abuse | Link to thisthe sagittal crest many people exhibit is a pretty clear phenotype from neanderathal interbreeding.
Reply | Report Abuse | Link to thisthe sagittal crest in particular is a clear phenotype from neanderathal interbreeding. profound science is important, but so is common sense.
Reply | Report Abuse | Link to thisHow does this fits with the statement made in "when the sea saved humanity" that we all descend fron a very small population... Where were the Neandertal during the period mentionned in that article?
Reply | Report Abuse | Link to this@skepticnc
Reply | Report Abuse | Link to thisThis idea about sharing 98.5% of our DNA with chimps is old, inexact, and missing critical information necessary to interpret what it means. More relevant questions would be: how many genes do we share with chimps? how many genes are similar, but there is a slight difference of a few base pairs, which results in a slightly different protein? how many genes are unique to chimps? how many genes are unique to humans? How much of the shared DNA is on coding versus non-coding regions?
None of this is well established, but that old 98.5% figure is definitely misleading. What it really means is that if you were to compare homologous DNA snippets in humans and chimps, you'd find about 1.5% difference (98.5% similarity) in the DNA sequences. But in addition to that, there are many segments of human DNA that have no homologue in the chimp (and vice versa) - meaning, there are proteins we code for that chimps simply don't produce. A study in 2006 at Uppsala University found that such regions accounted for about 6% of the protein coding regions.
Further, there is the question of how many of our genes are identical to those in chimps, and how many differ, even if only in 1-2 bases. The same study (which examined only chromosome 21) found that at least 13% of our genes differ from comparable genes in chimps, on chromosome 21. I dunno if the same numbers hold for other chromosomes, but it seems likely they do.
It's the same for the neanderthal study. If they say that we have 1-4% of neanderthal genes, that doesn't mean we have 1-4% of neanderthal DNA. You could have a gene, for example, which comes in 2 versions: human and neanderthal. What the study says is that some humans have about 1-4% genes in such neanderthal flavors. However, the neanderthal version may differ from the human version in only half a dozen nucleotide bases, out of tens of thousands. So the actual variation in DNA might only be 0.01% or some small number, if you were comparing in the same way as that human chimp study which found 98.5% similarity.
I don't know what a bonobo is, but I'd sure like to give one a shot ;)
Reply | Report Abuse | Link to thisgo humans!
It does seem that the advancement if not development of at least written language and art primarily occurred after the proposed genetic bottleneck about 70kya and roughly near the time it is thought that modern humans had extensive contact with neanderthals.
Reply | Report Abuse | Link to thisIt seems likely that these capabilities might significantly enhance our ability to successfully communicate with neanderthals, even if they did not share similar capabilities.
As I understand, while there is some evidence of individual expression and personal adornment prior to these times, much of the evidence of drawings and eventual writing is found around the Mediterranean region, near to where much of the interactions between modern humans and neanderthal populations would have been most likely to occur.
From this line of reasoning I suggest that modern humans owe much of our intellectual development to neanderthals, even if it was not imparted though genetic exchanges.
I remember reading rather recently that it was "unlikely that modern humans and Neandertals ever met, let alone bred". It went against what I had previously read over the years; and more importantly, my instincts, which are usually right, almost to a (strange) fault.
Reply | Report Abuse | Link to thisI absolutely agree that Neanderthals need to be reclassified as a subspecies of Homo sapiens as consistent with the findings of Green, Paabo et. al. However, I find Schermer's article to be silly and illogical. First of all, no matter how much sexual congress man has with another species, that wont make them into one species. Modern man and Neanderthals were able to interbreed not because they were sexually adventurous but because neither had differentiated so far from their common ancestral population to effect speciation. They were ALREADY one species! A second point that is more than silly, is his use of the concept that humans produce HYBRIDS by means of cultural conjoinings occuring as a result of migrations and travel. Those viable offspring are not hybrids, just regular HUMANS.
Reply | Report Abuse | Link to thisabby - I too agree with your sentiment - we are all biologically modern humans.
Reply | Report Abuse | Link to thisApparently, migrations out of highly populated regions have often occurred in large waves, as local conditions produce populations that exceed local resource availability and distant regions offer available or obtainable resources. The evidence might be simply summarized as:
- A pre-modern human population migrated out of Africa ~400kya, populating the Middle-East, Europe and Western Asia.
- The Toba supervolcano eruption in South East Asia nearly decimated the humans living in Africa approximately 74kya, reducing populations from about 1M to ~10k. A somewhat genetically differentiated population eventually recovered in Africa.
- The somewhat differentiated recovered modern human population migrated out of Africa ~80-50kya. Interbreeding with established earlier human populations, they migrated into the Middle East, Europe and Western Asia. Eventually interbred modern human populations migrated East throughout the Pacific.
The somewhat differentiated modern human population did not significantly return to Africa. As a result, modern human populations in Africa continued to regionally differentiate. They may have also continuously migrated out of Africa, or not. It can be said that Europeans and East Asians are more genetically similar than socially isolated neighboring groups in Africa.
We are all modern humans, but the generalized process described by the evidence allows for the development of differentiating characteristics supplied from slightly differentiated gene pools for the widely distributed populations of geographically and socially isolated modern human populations.
IMO, modern conditions produced by transportation and communication technologies, along with geographic saturation by globally dense populations of modern humans are minimizing the effects of isolating influences. This recently saturating population of post modern humans may not survive for long as resources requirements exceed their production capabilities, but there is now greater potential for high volume development of newly differentiated gene pools than ever before, even disregarding any explicit technological manipulation. Of course, there is also now an increasing risk of high volume population decimation by pathogens or other effects...
Beautifully elucidated, jtdwyer. I especially appreciated your comments, all three times, that referred to the likelihood that human development advanced significantly due to contact between the modern wave and Neantherthal wave (to simplify their designations) whether because of non-genetic or genetic influence of such contact. I am inclined to believe that genetic contact was important in this development, as there is generally increased strength accruing from the mixture of gene pools, which fosters the preservation of the best traits of each.
Reply | Report Abuse | Link to thisabby - Thanks for the kind words. I suspect you're right about genetic exchanges being important to the development of symbolic encoding of abstract communication, but I think the functional requirements imposed by potentially differentiated communications abilities of the two groups could also have strongly influenced development of communications skills enhancements in both populations. This development was not likely just a chance result of interbreeding, but likely was enhanced by it.
Reply | Report Abuse | Link to thisThat nothing became something to evolve a brain into self explanation goes for insane -- matter is dimensional -- how small does small get ?-- how large does large get ?-- that anything exists eliminates all doubt whatever forms dimensional is a latent form without.
Reply | Report Abuse | Link to thisAbby,
Reply | Report Abuse | Link to thisRefer to my comment above.
"To clarify, Mayr had <a href="http://www.pnas.org/content/102/suppl.1/6600.full">two concepts of species</a>: his species as metapopulation lineage and his species as intrinsic reproductively isolated population. There is across the board acceptance of the first definition, but not the second -- last I checked. Under both definitions, organism which cannot potentially produce viable offspring belong to separate species. Only under the second definition do organisms which can produce viable offspring necessarily belonging to the same species. In that sense, dogs, dingos, jackals, and coyote necessarily belong to the same species. And numerous plant species. "
There is a complex unresolved debate in biology as to what constitutes as species. If you change the definition to mean "can produce viable offspring" you change it for all species.