A New Human Species?
First there were several species of humans, at least from the perspective of some Western naturalists who considered Africans a separate species. But it soon became apparent to biologists that all people of the earth are one species. Darwin raised the possibility that we evolved from other species, and this was apparently confirmed with the discovery of Neanderthal man. It turns out Neanderthals are our cousins, not our ancestors, but with them there have been at least two species that can be called “human” on this planet.
And that was the status of things for a while. Homo erectus and Homo habilis extended the number of species in our genus (it’s debatable whether habilis should really be an Australopithecus), but they are not close enough to us to be considered human cousins. More recently several species have been identified at the root of humans and neanderthals. Homo heidelbergensis is probably our direct ancestor from about 650,000 years ago. But there is also Homo antecessor, which (along with heidelbergensis) likely evolved from Homo ergaster in Africa.
Then a third recent close human cousin was discovered – Homo floresiensis, or the Hobbit. This is still controversial, but the data is leaning in the direction of concluding that a diminutive species of human lived until about 12,000 years ago on the island of Flores. We missed by a geological hair’s breath there being as many as three distinct human species occupying the earth. Given the problems we have had with race relations, I have often wondered how our society would deal with an actual distinct species.
Now, as announced in Nature magazine, there could be a fourth species of human to have occupied the earth as recently as 30,000 years ago. The specimen is called Woman-X and it was found in Siberia, at a site which also contains modern humans.
The new evidence is mitochondrial DNA from the pinky bone of Woman-X. The analysis shows features in common with modern humans – the specimen is clearly human – but also differences between both modern humans and neanderthals. So if Woman-X was human, but not modern and not neanderthal – what was it? That is the exciting news – perhaps it was a new species. If so then there were at least three human species co-mingling around Europe and Asia 40,000 years ago or so (Homo floresiensis was isolated on the island of Flores.)
We discussed this news item on the SGU this week and have had some interesting feedback. One listener pointed me to John Hawkes blog where he discusses the alternate interpretation that Woman-X may simply be from a branch or clade of neanderthals with a separate mitochondrial lineage that was uncommon. He makes the point that genetic lineages are not necessarily the same thing as “species”, to which I would add that the very notion of “species” is fuzzy.
Of course this is a preliminary analysis – one specimen and mitochondrial DNA only. Somatic DNA analysis is apparently underway. This may clarify the issue, but we may also need more specimens before we can confidently conclude that Woman-X was a member of a distinct human species.
Part of the analysis is about divergence time – when was the last common ancestor between two species. Humans share a last common ancestor with neanderthals about 500,000 years ago, but other estimates put it at 660,000 years. The Woman-X analysis suggests a last common ancestor with modern humans about 1 million years ago. If true this would definitely make it a distinct species, and suggest a separate and earlier migration out of Africa. But, as Hawkes points out, divergence time conclusions are highly dependent on sampling size – how many different genes are you looking at among how many individuals?
There are a few take-home messages from this research:
The evolution of humans is far more complex than previously imagined, and it is very likely that our picture of human evolution over the last million years will get much more complex. There apparently were multiple migrations out of Africa to Europe and Asia, with multiple early branchings. This is likely further complicated by various amounts of time in which different branches continued to interbreed when they overlapped. The more detailed a picture we get, the more complex and fuzzy it is likely to become.
This new evidence is very preliminary, and only raises the possibility of a new distinct species, but other interpretations are still viable. Clarifying this will have to wait for further analysis of this specimen, but also likely the discovery of new specimens.
I have not mentioned this point yet, but this research also raises the question of how much we can use culture as a proxy for species. In other words, when we find certain tools that tend to go along with a certain human species, can we be confident that that species in fact made and used them? How much cultural and technological contamination was there among the overlapping human species?
Also, when reporting on a new science item it is almost universally true that when the scientific community starts to take a close look at the research new interpretations will emerge, perhaps even errors pointed out. That is the cycle of science. But this means that early reporting of the new science publication is likely to be followed by more expert analysis that calls the original conclusions into question. This is why we often say that we will “follow this story” – we need to follow the process of science as it plays out. So take science news items with a grain of salt – new information is by its very nature tentative.
In fact what I find most interesting about these stories is watching the process of science – reading about how different scientists argue their cases tells us a great deal about the state of the evidence, and also about the kinds of arguments scientists use and how they interpret the evidence – how we know what we know.
No matter how this particular story pans out, it is likely to be highly interesting.
How much of the record is missing underwater? I found a map of what the coastline looked like 18,000 years ago here: http://www.ngdc.noaa.gov/mgg/topo/globega2.html . The differences are stunning. The British Isles are merely an extension of the continent, as are the islands in Indonesia. I never see this mentioned in analyses of pre-historic man. Throughout history many humans lived close to the shore. More weight needs to be given to the affect that the much lower sea-levels had on humans at this crucial point in history.
One idea that is growing in popularity is that Homo Sapiens evolved our signature “big brains” as a result of adaptation to condition changes, and not the new conditions themselves. The supporting evidence is in sediment layers in Africa showing areas that rapidly seesawed between habitable and uninhabitable. This forced nature’s hand into evolving a species able to adapt immediately to environmental changes without mutation: homo sapien.
If that is plausible, wouldn’t it be possible then that Woman-X is a descendant of early humans, rather than an ancestor? Siberia was one of the most unforgiving environments on the planet 30,000 years ago, and still is today. One thing it did not do though, was change very much. If newly-spawned humans migrated to another region where conditions were more static (like Siberia), the lack of dynamic environment and need for energy conservation could have caused the brain to mutate back to a smaller size in order to save energy in the harsh cold climate, just as bipedalism emerged to save energy while walking.
This is not “devolution”, but a natural mechanism we’ve seen in a number of other species. An amphibious animal might lose its toe webbing in favor of digging claws over a long period if its habitat dries up, but the knowledge of webbed toes remains stored in its genes, ready to be reactivated as needed.
Why would any human species would find it preferable to migrate to an unforgiving environment, such as Siberia, when there were endless opportunities in milder more hospitable climes for establishing communities. It’s a real wonderment.
Boredom. It is the signature of human condition.
Even Homo Sapiens sapiens were put in zoos. Other primate species are put in zoos or killed for food. I don’t wonder at all how a different humanoid species would be treated.
They would certainly have been converted to Christianity long ago.
One of the things that I find fascinating, especially given discoveries like this, is how genetically indistinct humanity is. You’d expect that a species that has been around for a couple million years would have heavily varied sub-species, but we really don’t. There are cosmetic differences between the so-called races (which have far, far, far more in common than, for example, races of different dogs, or even horses/zebras and chimps/bonobos), but genetically that’s just about it from what I’ve gathered.
This is further proof that we descended from Christian space aliens, and that is why vaccines give us autism cancer.
Several genetic bottlenecks have occurred (some estimated down to a few thousand individuals) which would have greatly decreased genetic diversity. I understand your point and agree, but dogs or other domestic animals may not be the best example as they just show how flexible limited genetics can be when subjected to artificial selection. I bet we could get some of the same kinds of results even within the limited genetics of humans if we were willing to subject each other to that kind of selection.
One well documented genetic bottleneck is from around 70,000 years ago (well before the world was even created). Many speculate this was the result of a super volcano that blew it’s top in the region of the world where Malaysia currently sits.
And yes, the huan species has a very small genetic diversity for a mamilian species. Such lack of diversity is actually a very bad trait, and could spell the doom of our species!
I can see only two explanations for this Woman-X:
One, she is the product of an alien human hybrid. Thus explaining the DNA issues.
Or two, as Robo Sapien says, she’s one of homo sapien’s biological descendents, only she is from the future! Which explains why she is the only specimen. She came back in time and got trapped here.
I love science! ;-)
Perhaps she told that very same joke, and time itself just stopped as the entire human species failed to laugh.
It seems more likely then not that Neanderthals didn’t simply disappear but were incorporated into the genetic pool. — It also is more likely that the first immigrants to the new world did not walk here over 6000 miles of ice but arrived on boats or rafts. I do know how difficult that journey would be for ancient mankind but I also know it would be far easier then traveling that distance on ice and snow. — One more less controversial point: probably most important evolutionary changes, such as bigger brains, were not a slow process but a sudden change as a result of a fortunate birth defect or anomaly. These happen all the time and when they favor survival they flourish.
I’m sorry, but that is all incredibly wrong. Did you check ANY facts before you wrote that? I hate to sound mean, but that kind of ignorant spouting is completely counter-productive to skepticism.
The migration was not a road trip, it was a long process of inching towards more favorable climate. Furthermore, the discovery of a neanderthal boat would turn the science on its head. As for the brains, it WAS a slow process. We didn’t spontaneously mutate an amazing super brain one day and go “Aw sweet, I’m smart dude!”