Neanderthals were already on the verge of extinction in Europe by the time modern humans arrived on the scene, a study suggests.
DNA analysis suggests most Neanderthals in western Europe died out as early as 50,000 years ago - thousands of years before our own species appeared.
A small group of Neanderthals then recolonised parts of Europe, surviving for 10,000 years before vanishing.
The work is published in the journal Molecular Biology and Evolution.
An international team of researchers studied the variation, or diversity, in mitochondrial DNA extracted from the bones of 13 Neanderthals.
This type of genetic information is passed down on the maternal line; because cells contain multiple copies of the mitochondrial genome, this DNA is easier to extract from ancient remains than the DNA found in the nuclei of cells.
The fossil specimens came from Europe and Asia and span a time period ranging from 100,000 years ago to about 35,000 years ago.
The scientists found that west European fossils with ages older than 48,000 years, along with Neanderthal specimens from Asia, showed considerable genetic variation.
But specimens from western Europe younger than 48,000 years showed much less genetic diversity (a six-fold reduction in variation compared to the older remains and the Asian Neanderthals).
In their scientific paper, the scientists propose that some event - possibly changes in the climate - caused Neanderthal populations in the West to crash around 50,000 years ago. But populations may have survived in warmer southern refuges, allowing the later re-expansion.
Low genetic variation can make a species less resilient to changes in its environment, and place it at increased risk of extinction.
"The fact that Neanderthals in Europe were nearly extinct, but then recovered, and that all this took place long before they came into contact with modern humans, came as a complete surprise," said lead author Love Dalen, from the Swedish Museum of Natural History in Stockholm.
"This indicates that the Neanderthals may have been more sensitive to the dramatic climate changes that took place in the last Ice Age than was previously thought."
Neanderthals were close evolutionary cousins of modern humans, and once inhabited Europe, the Middle East and Central Asia. The reasons behind their demise remain the subject of debate.
The appearance of modern humans in Europe around the time of the Neanderthal extinction offers circumstantial evidence that Homo sapiens played a role. But changes in the climate and other factors may have been important contributors.
"The amount of genetic variation in geologically older Neanderthals as well as in Asian Neandertals was just as great as in modern humans as a species," said co-author Anders Gotherstrom, from Uppsala University.
"The variation among later European Neanderthals was not even as high as that of modern humans in Iceland."
The researchers note that the loss of genetic diversity in west European Neanderthals coincided with a climatic episode known as Marine Isotope Stage Three, which was characterised by several brief periods of freezing temperatures.
These cold periods are thought to have been caused by a disturbance of oceanic currents in the North Atlantic, and it is possible that they had a particularly strong impact on the environment in western Europe, note the researchers.
Over the last few decades, research has shown that Neanderthals were undeserving of their brutish reputation.
Researchers recently announced that paintings of seals found in caves at Nerja, southern Spain, might date to 42,000 years - potentially making them the only known art created by Neanderthals. However, this interpretation remains controversial.
Also, the Toba eruption of app. 70,000 yrs. ago, gave rise to what has become known as a genetic bottleneck, reducing the breeding pairs of humans to as low as 1,000 people. That is why our genome is so harmonius. Of course, my friend, there is disagreement on this as well. Some are saying there was a "long" bottleneck, due not only to climatological disaster, but food source availablility, biological hazards, and any myriad of other problems arising. Nevertheless, mitochondrial Eve, app. 150,00 yrs. ago is the mother of us all. And no, she was not a human/cylon hybrid. Ha ha. So lets all realize that we are family. Individuals, yes, but the only extant species of homo. Makes me proud to call you brother. For that is true, in every sense of the word.
Brothers and sisters, after all those years, still not able to live in peace and harmony. I wonder ... Will we ever learn?
It hard to imagine such a small population spread over the inhabited world. What was the inhabited world at that particular time ? Would we say our species was still confined to Africa or had spread as far as India as is suggested by the finding of stone tools which both pre-date and post-date the time of eruption ?
The experts appear to be split on this one.
[Standard disclaimer--Since this is science, and even worse, archaeology, everything I am about to say is provisional and subject to change as new evidence comes in.]
The dominant (for what it is worth) thought at the moment is at the time of Toba modern humans had at least reached India. The movement out of Africa wasn't radial, but channeled along the Indian Ocean coastlines. So the "inhabited world" was pretty small. The effects of Toba would have been severe across that area. The surviving population wouldn't have been spread evenly across that area, but clustered in isolated pockets, so you'd still have viability.
There are other explanations for that particular genetic bottleneck, but it is hard to see Toba not having a huge effect.
Of course, there could be multiple causes of the genetic bottleneck which occurred around the time of the Toba eruption.
With a human population stretching from Africa to India surely it could not have been reduced to 1000 breeding pairs as has been suggested by some experts.
You're right. The investigatiion is continuing.
The estimates for that bottleneck range from a 50-90% population drop. 1000 is the lower end of the range, and the human population was not large to begin with. I have no problem with the idea that a catastrophe on the scale of Toba could drastically reduce populations over an area that size, or even globally. It's not just the eruption itself, but the environmental and climatic aftermath. For example, a comparatively tiny eruption in 1815 (Mount Tambora) caused "the year without a summer." With Toba, we are conservatively looking at decades without a summer.
I spent some time at Lake Toba in my youth. The crator lake has an island with basic accommodations without electricity or sanitation. It felt very peaceful.
I accept what you say about volcanic devastation and would like to think of a population drop closer to 50 %
Joan, I may be overly optomistic, but I hope so. We definately have the ability to do so.
This is old news, apparently, but new to me. Last I heard, there was no DNA evidence that Homo Sapiens had interbred with Neanderthals. Seems in 2010 they found some in 1%-4% of the Eurasian human genome. Thought people here would find that interesting if they didn't know already.
Thank you for the National Geographic article dated 6 Oct 2010.
I've always thought of myself as a Neanderthal, anyway. It's interesting that not all human populations have Neanderthal genes too. You have and Nelson Mandela doesn't have Neanderthal genes according to this DNA research.
I know! Weird, huh?
I got my "no interbreeding" theory from Alice Roberts series you mentioned. Love her! Science is so sexy!!!
Do you think her 'no breeding' theory is based too much on a feminine perspective of mammal mating rather than considering a masculine perspective ? For example, in nature the male of many species competes with other males for access to females while the female can be selective in her choice of mating partner ?