A new research has found evidence to suggest that climate change, rather than hunting, was the main factor that drove the woolly mammoth to extinction.
A DNA analysis shows that the number of creatures began to decrease much earlier than previously thought as the world’s climate changed.
The study also shows that there was a distinct population of mammoth in Europe that died out around 30,000 years ago.
The results have published in the Proceedings of the Royal Society B.
The view many researchers had about woolly mammoths is that they were a hardy, abundant species that thrived during their time on the planet.
But according to the scientist who led the research, Dr. Love Dalen of the Swedish Museum of Natural History, the study shifts that view.
Dr. Love Dalen worked with researchers in London to analyze DNA samples from 300 specimens from woolly mammoths collected by themselves and other groups in earlier studies
The scientists were able to work out how many mammoths existed at any given time from the samples as well as tracing their migration patterns. They looked at the genetic diversity in their samples – the less diverse the lower the population.
Climate change, rather than hunting, was the main factor that drove the woolly mammoth to extinction
They found that the species nearly went extinct 120,000 years ago when the world warmed up for a while. Numbers are thought to have dropped from several million to tens of thousands but numbers recovered as the planet entered another ice age.
The researchers also found that the decline that led to their eventual extinction began 20,000 years ago when the Ice Age was at its height, rather than 14,000 years ago when the world began to warm again as previously thought.
They speculate that it was so cold that the grass on which they fed became scarce. The decline was spurred on as the Ice Age ended, possibly because the grassland on which the creatures thrived was replaced by forests in the south and tundra in the north.
The reason they died out has been a matter of considerable scientific debate. Some have argued that humans hunted them to extinction while others have said that changes in the climate was the main factor.
A criticism of the climate extinction argument is that the world warmed well before the creatures became extinct and so that could not have been the cause.
The new results show that mammoths did indeed nearly go extinct between Ice Ages and so backs the view that climate change was the principal cause for their demise.
These results back a computer simulation of conditions at the time carried out by researchers at Durham University in 2010.
And of course other animals, including humans, became more active after the Ice Age and so competition with other species and hunting may also have been a factor in their extinction, though not the principle cause, argues Prof. Adrian Lister of the NHM.
“During the last ice age, between about 50,000 and 20,000 years ago, there were substantial movements of mammoth populations – European populations being replaced by waves of migration from the east, for example,” he said.
“But from about 20,000 years ago onwards, the population started the dramatic decline that led to its extinction, first on the mainland about 10,000 years ago, and finally on some outlying Arctic islands. The pattern seems to fit forcing by natural climate change: any role of humans in the process has yet to be demonstrated.”
New details have been revealed after DNA analysis was performed on what could be described as the world’s oldest murder case of Otzi the “Iceman”, whose 5,300-year-old body was discovered frozen in the Italian Alps in 1991.
Otzi’s full genome has now been reported in Nature Communications.
DNA analysis reveals that Otzi had brown eyes, “O” blood type, was lactose intolerant, and was predisposed to heart disease.
They also show him to be the first documented case of infection by a Lyme disease bacterium.
Analysis of series of anomalies in the Iceman’s DNA also revealed him to be more closely related to modern inhabitants of Corsica and Sardinia than to populations in the Alps, where he was unearthed.
The study reveals the fuller genetic picture as laid out in the nuclei of Otzi’s cells.
This nuclear DNA is both rarer and typically less well-preserved than the DNA within mitochondria, the cell’s “power plants”, which also contain DNA.
Otzi’s mitochondrial DNA had already revealed some hints of his origins when it was fully sequenced in 2008.
Albert Zink, from the Eurac Institute for Mummies and the Iceman in Bolzano, Italy, said the nuclear DNA study was a great leap forward in one of the most widely studied specimens in science.
“We’ve been studying the Iceman for 20 years. We know so many things about him – where he lived, how he died – but very little was known about his genetics, the genetic information he was carrying around,” Albert Zink said.
A reconstruction shows how Otzi the Iceman may have looked like before an arrow felled him
Otzi was carrying around a “haplotype” that showed his ancestors most likely migrated from the Middle East as the practice of formal agriculture became more widespread.
It is probably this period of transition to an agrarian society that explains Otzi’s lactose intolerance.
Prof. Albert Zink said that next-generation “whole-genome” sequencing techniques made the analysis possible.
“Whole-genome sequencing allows you to sequence the whole DNA out of one sample; that wasn’t possible before in the same way.
“This was really exciting and I think it’s just the start for a longer study on this level. We still would like to learn more from this data – we’ve only just started to analyse it.”
A new study suggests that Neanderthals were already on the verge of extinction in Europe by the time modern humans arrived on the scene.
The study used DNA analysis which revealed 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 recolonized 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).
A new study suggests that Neanderthals were already on the verge of extinction in Europe by the time modern humans arrived on the scene
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 Neanderthals 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 characterized 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.