An image of a Neanderthal woman at the National Archaeological Museum of Madrid. New research suggests that only a 2% decrease of the fertility rates would have driven the Neanderthals to extinction.
Neanderthals would have become extinct as a result of a slight decrease of the fertility rates, a new study found.
The last of the Neanderthals, the closest extinct relatives of modern humans, disappeared from Europe around 40,000 years ago. Earlier research estimated that at its peak, the entire Neanderthal population in Europe and Asia was relatively small, a total of 70,000.
Scientists have long debated the question of whether the spread of modern humans around the world, helped kill Neanderthals, either directly through conflict and indirectly through the spread of the disease.
“The disappearance of the Neanderthal population is an exciting topic, imagine a group of people who lived thousands of years and is very well adapted to its environment, and then disappears,” study senior author Silvana Condemi, a paleoanthropologist at Aix-Marseille University in Marseille, France, told Science. “For a long time it was thought that Homo sapiens had just killed the Neanderthals. Today, thanks to the results of the genetic analysis, we know that encounters between Neanderthals and sapiens were not always so cruel, and that incestuous place — even today, people have the genes of Neanderthal origin.” [Top 10 Mysteries of the First Humans]
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Instead of investigating why the Neanderthals disappeared, “we have looked for the ‘how’ of their demise,” Condemi said. Specifically, the scientists generated computer models that examined how Neanderthal populations may decline and extinction over time in response to a variety of factors, such as war, epidemics, and impaired fertility, or the survival of men and women of different ages.
“Very quickly, we found something unexpected — this disappearance, which extends over a very long period of time, can not be explained by a catastrophic event,” Condemi said. Computer models that assumed that modern humans killed off Neanderthals by war or epidemics found that these factors would have driven the Neanderthals to extinction much faster than the 4,000 to 10,000 years in the archaeological finds, during which modern man and the Neanderthals were known included in Europe, the researchers said.
The scientists also found that neither an increase in juvenile or adult survival, nor a strong decrease of the birth rates, were likely causes for the long decline seen in the Neanderthals. Instead, they discovered that the extinction of the Neanderthals was possible within 10,000 years, and a 2.7% decline in the fertility rates of young Neanderthal man-women — first-time mothers less than 20 years old and within 4,000 years with an 8% decline of the birth-rate in the same group.
“The disappearance of the Neanderthals was probably due to a slight decline in fertility among the youngest women,” Condemi said. “This is a phenomenon that is limited in size so that about the time, had an impact.”
A variety of factors could have reduced these fertility rates. Condemi noted that pregnancies among young, first-time mothers are on average more risky than the second or subsequent pregnancies. A minimum of calories, it is necessary for the maintenance of pregnancy, and a reduction of food, and therefore calories, it is harmful to the pregnancy.”
The neanderthals disappeared in a time of climate change. Environmental fluctuations can lead to a slight decrease in food, and in turn “may explain a reduction of the fertility,” Condemi said.
Condemi noted that prior work has suggested that the modern man “as the average number of births drops to a level of 1.3 among the women of the world, our species would disappear in 300 years. This is an unlikely model, but the results are very, very fast!”
The scientists detailed their findings online May 29 in the journal PLOS ONE.
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Originally published on Live Science.