New Studies Clash with Previous Analyses On the Life and Fate of Neanderthals
Two new studies have emerged in the past week claiming to provide more details than ever about the Neanderthal’s genetic contribution to the modern population plus a new theory on how it eventually lost out to modern humans.
Science Daily reports that a new study suggests that Neanderthal-Denisovan lineage nearly went extinct after separating from modern humans. The new study’s finds challenge the conventional wisdom about modern humans, Neanderthals and Denisovans.
The Economic Times among others has reported on a different study that has found that later in the evolutionary time line, contrary to earlier theory, similarity of diet is responsible for the downfall of Neanderthals in favor of homo sapiens.
New Method for Analyzing Archaic DNA – Against Conventional Wisdom
A University of Utah-led team has developed a new method for analyzing archaic DNA in order to reconstruct early history of archaic human populations. The new study found that the Neanderthal-Denisovan lineage nearly went extinct after separating from modern humans. Almost three hundred generations later, Neanderthals and Denisovans separated from each other. That calculates at nearly 744,000 years ago, much earlier than any other estimation of the split. "If Neanderthals and Denisovans had separated later, then there ought to be more sites at which the mutation is present in the two archaic samples, but is absent from modern samples," Alan Rogers, professor in the Department of Anthropology and lead author of the study, said as Science Daily reports.
These population trees with embedded gene trees show how mutations can generate nucleotide site patterns. The four branch tips of each gene tree represent genetic samples from four populations: modern Africans, modern Eurasians, Neanderthals, and Denisovans. In the left tree, the mutation (shown in blue) is shared by the Eurasian, Neanderthal and Denisovan genomes. In the right tree, the mutation (shown in red) is shared by the Eurasian and Neanderthal genomes. (Credit: Alan Rogers, University of Utah)
The diagram shows a first separation into African/Eurasia strands and Neanderthal/Denisovan. The mutation gene detected then later becomes present in the previously separate Neanderthal and Eurasia populations.
Next the researchers claim, the global Neanderthal population grew to tens of thousands of individuals living in fragmented, remote populations dispersed across Eurasia. "This hypothesis is against conventional wisdom, but it makes more sense than the conventional wisdom," said Rogers.
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Neanderthal man at the Natural History Museum London (CC BY-NC-ND 2.0)
Non-Traditional Evolutionary Story
Previous scientific calculations of the Neanderthal population size were very small, nearly a thousand individuals. "There's a rich Neanderthal fossil record. There are lots of Neanderthal sites," Rogers says as Science Daily reports. And added, "It's hard to imagine that there would be so many of them if there were only 1,000 individuals in the whole world."
For that matter, a 2015 study correlates with the new finds, as it indicated that the initial estimates underrepresent the number of individuals if the Neanderthal population was subdivided into remote, regional groups. The Utah team now claims that this explains the inconsistency between previous estimates and their own much larger estimate of Neanderthal population size. "Looking at the data that shows how related everything was, the model was not predicting the gene patterns that we were seeing. We needed a different model and, therefore, a different evolutionary story,“ Ryan Bohlender, post-doctoral fellow at the M. D. Anderson Cancer Center at the University of Texas, and co-author of the study stated as Science Daily reports. Furthermore, the team developed an improved statistical method, called legofit that accounts for multiple populations in the gene pool, which appears to support previous estimates of gene flow from Neanderthals into modern Eurasians.
Neanderthal mother and child (Anthropos Pavilion, Brno, Czech Republic) (CC BY-NC 2.0)
A Family Affair in DNA
Natural mutations occur in the 3.5 billion or so nucleotide sites present in the human genome and these mutations get passed down in the DNA of a family, making the lineage trackable. It is not an exact science, but from this data scientists can estimate with some degree of accuracy when groups diverged or split from each other genetically, providing evolutionary history hundreds of thousands of years in the past. These clues to changing populations are small, but they are traceable.
“You're trying to find a fingerprint of these ancient humans in other populations. It's a small percentage of the genome, but it's there," Rogers tells Science Daily.
Using this fresh approach, the team from University of Utah compared the genomes of four human populations: Modern Eurasians, modern Africans, Neanderthals and Denisovans. The modern samples came from Phase I of the 1000-Genomes project and the archaic samples came from the Max Planck Institute for Evolutionary Anthropology. The studied a few million nucleotide sites that shared a gene mutation in two or three human groups, and established 10 distinct nucleotide site patterns. From this they could draw their new conclusions.
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What Caused the Extinction of Neanderthals?
Interestingly, in a separate study conducted by scientists from the Senckenberg Centre in Tübingen, southwest Germany, suggests that the “battle” for food (consisting mainly of mammoth and plants) between early modern humans and Neanderthals led to the extinction of the Neanderthals. Previous research suggested that early modern humans had a more varied diet than the Neanderthals, indicating they fished for their food and did hunting and gathering across the plains. "Many studies examine the question of what led to this displacement -- one hypothesis postulates that the diet of the anatomically modern humans was more diverse and flexible and often included fish," added Herve Bocherens from the University of Tubingen. The theory followed that their more diverse diet allowed them to survive when the Neanderthals could not.
However, the finding of the more recent Senckenburg study disputes this.
"According to our results, Neanderthals and the early modern humans were in direct competition in regard to their diet, as well -- and it appears that the Neanderthals drew the short straw in this contest," said Dorothee Drucker, biogeologist from the University of Tubingen in Germany, as The Economic Times report.
Pleistocene of Northern Spain showing woolly mammoth, cave lions eating a reindeer, tarpans, and woolly rhinoceros. (CC BY 2.5)
For the study, the scientists examined the dietary habits of early modern man on the basis of the oldest known fossils from the Buran Kaya caves on the Crimean Peninsula in the Ukraine. Next, they measured the percentage of stable carbon and nitrogen isotopes in the bones of the early humans and the locally present potential prey animals such as Saiga, horse, and deer. “The results revealed a very high proportion of the nitrogen isotope 15N in early modern humans, which originate primarily from the consumption of mammoths,” Bocherens told The Economic Times.
This makes the diet of the early humans and Neanderthals more similar than was thought, meaning they were competing for the same food. This competition was ultimately won by the early humans, the researchers conclude. Early humans didn’t survive by being able to exploit different food sources but by winning the competition for food that they all sought. The question of exactly how they were more successful opens a fresh argument that will definitely cause a buzz and debate within scientific circles.
Top image: Weakened Neanderthal amongst plant foodstuff (CC BY-NC-ND 2.0)