Beringia...Land of the Mammoth Hunters!
A Rich Collection of Fossils from Fonelas P-1, SpainOpen Access Anthropology Papers over at the American Museum of Natural History October 31, 2007...3:09 pm Peopling of the Americas: mtDNA tells us of the Beringian Standstill Jump to Comments A new study of over 600 mtDNAs from 20 American and 26 Asian populations is shedding some unique insight on how the Americas were peopled. As you may have been taught, it was thought that the Americas were founded by a not so diverse founding population or two. Before this paper, only about 70 left their genetic print in modern descendants, a very small but effective founder population.
But, there are new results, which were published almost two months ago, that show that there was much more genetic diversity in the founder population than was previously thought. I didn’t catch it until I saw both Razib and Science Daily report on it a couple days ago.
The paper, “Beringian Standstill and Spread of Native American Founders,” was published in the freely accessible PLoS One. Beringia is a fancy way of naming the Bering Land Straight that once connected the north east Asia continent to north west America continent.
One of the more interesting lines of evidence they found from their sequence comparison and their revised phylogenetic map is that the ancestral population literally chilled out in Beringia for a long time. The authors estimate about 15,000 years. That’s long enough so that specific mutations accumulated which separated the New World founder lineages from the Asian sister-clades.
The other more interesting thing that was uncovered was that the founding haplotypes are uniformly distributed across North and South America. They do not show a nested structure from north to south. That means that after what the authors are terming the Beringian standstill and what I’m calling the Beringian chillout, the initial North to South migration was very swift. It was not a gradual diffusion.
And as Razib pointed out in his post, during the last 30,000 years, there was a lot more bouncing back and forth from Northeast Asia and North America. The analysis shows that there was a series of back migrations to Northeast Asia as well as forward migrations to the Americas from Beringia, “more recent bi-directional gene flow between Siberia and the North American Arctic.”
Overall, this study tells us a lot on how people were moving about in the northern hemisphere. But what about oceanic travel, and the recent chicken population genetic similarities? They seem to have made some cultural if not genetic contribution to populations here.
Related sidenote, I like how this study one ups an older PLoS paper, which I reffered to above (the 70 people one). If you want, check out that paper, “On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas.”
But, there are new results, which were published almost two months ago, that show that there was much more genetic diversity in the founder population than was previously thought. I didn’t catch it until I saw both Razib and Science Daily report on it a couple days ago.
The paper, “Beringian Standstill and Spread of Native American Founders,” was published in the freely accessible PLoS One. Beringia is a fancy way of naming the Bering Land Straight that once connected the north east Asia continent to north west America continent.
One of the more interesting lines of evidence they found from their sequence comparison and their revised phylogenetic map is that the ancestral population literally chilled out in Beringia for a long time. The authors estimate about 15,000 years. That’s long enough so that specific mutations accumulated which separated the New World founder lineages from the Asian sister-clades.
The other more interesting thing that was uncovered was that the founding haplotypes are uniformly distributed across North and South America. They do not show a nested structure from north to south. That means that after what the authors are terming the Beringian standstill and what I’m calling the Beringian chillout, the initial North to South migration was very swift. It was not a gradual diffusion.
And as Razib pointed out in his post, during the last 30,000 years, there was a lot more bouncing back and forth from Northeast Asia and North America. The analysis shows that there was a series of back migrations to Northeast Asia as well as forward migrations to the Americas from Beringia, “more recent bi-directional gene flow between Siberia and the North American Arctic.”
Overall, this study tells us a lot on how people were moving about in the northern hemisphere. But what about oceanic travel, and the recent chicken population genetic similarities? They seem to have made some cultural if not genetic contribution to populations here.
Related sidenote, I like how this study one ups an older PLoS paper, which I reffered to above (the 70 people one). If you want, check out that paper, “On the Number of New World Founders: A Population Genetic Portrait of the Peopling of the Americas.”
Megafauna of Ice Age Washington
The Japan Times
November 15, 2001
By SUSAN OKIE
The Washington Post
Megafauna extinction mystery
WASHINGTON — As recently as 20,000 years ago, North America had an array of large mammals to rival the spectacular wildlife of modern Africa. Mammoths bigger than African elephants, as well as smaller, pointy-toothed mastodons, ranged from Alaska to Central America. Herds of horses and camels roamed the grasslands, while ground sloths the size of oxen lived in the forests and bear-size beavers built dams in streams. By about 10,000 years ago, all these animals — and others, such as saber-toothed cats and giant bears — were gone. Some 70 North American species disappeared, three-quarters of them large mammals. Why? The question has fascinated archaeologists, geologists, biologists and anthropologists for decades. One long-popular theory holds that the Clovis people, Stone Age immigrants from Asia who appeared in North America about 11,000 years ago, swept across the continent and hunted most of its large mammals to extinction. But proponents of alternative theories suggest that the animals died of natural causes. According to one view, rapid climate shifts at the end of the Ice Age altered the pattern of North American vegetation, shrinking the habitats of the big mammals until they became extinct. Another scenario casts human immigrants (or perhaps animals or insects they brought with them) as unwitting deliverers of a killer virus that devastated the continent's wildlife.
November 15, 2001
By SUSAN OKIE
The Washington Post
Megafauna extinction mystery
WASHINGTON — As recently as 20,000 years ago, North America had an array of large mammals to rival the spectacular wildlife of modern Africa. Mammoths bigger than African elephants, as well as smaller, pointy-toothed mastodons, ranged from Alaska to Central America. Herds of horses and camels roamed the grasslands, while ground sloths the size of oxen lived in the forests and bear-size beavers built dams in streams. By about 10,000 years ago, all these animals — and others, such as saber-toothed cats and giant bears — were gone. Some 70 North American species disappeared, three-quarters of them large mammals. Why? The question has fascinated archaeologists, geologists, biologists and anthropologists for decades. One long-popular theory holds that the Clovis people, Stone Age immigrants from Asia who appeared in North America about 11,000 years ago, swept across the continent and hunted most of its large mammals to extinction. But proponents of alternative theories suggest that the animals died of natural causes. According to one view, rapid climate shifts at the end of the Ice Age altered the pattern of North American vegetation, shrinking the habitats of the big mammals until they became extinct. Another scenario casts human immigrants (or perhaps animals or insects they brought with them) as unwitting deliverers of a killer virus that devastated the continent's wildlife.
Above: A Giant Tree Sloth
Did hunters wipe out the American megafauna?
Did climate change do it?
Or was it a plague?
Scientists are limited by what can be proved through examinations of fossils and stone spear points. Fossils can't tell precisely when animal populations died out, although they can suggest an approximate chronology. In rare cases, genetic or immunological tests on well-preserved soft tissues may yield evidence of infectious diseases. Paul Martin, professor emeritus of geosciences at the University of Arizona in Tucson, is the most vigorous proponent of the "overkill" theory. Because so many species of large American mammals disappeared about 11,000 years ago, he argues, over-hunting by the new arrivals is the most plausible explanation. There are abundant examples of extinction occurring soon after humans arrived on islands, apparently caused by hunting, and Martin believes the same thing could have happened continent-wide. "People can do it really fast and it won't leave much evidence behind," he said. The Clovis people "found a favorable environment. Their numbers would increase without serious limit, at a really rapid rate. Within 1,000 years, our species had swept through the Americas." But critics say that if Clovis hunters killed off the mammals, there should be more fossil evidence of the deed. Clovis people's stone weapon points have been found in association with mammoths, mastodons and bison but not with other mammals, noted Russell Graham, chief curator at the Denver Museum of Nature and Science.
Did climate change do it?
Or was it a plague?
Scientists are limited by what can be proved through examinations of fossils and stone spear points. Fossils can't tell precisely when animal populations died out, although they can suggest an approximate chronology. In rare cases, genetic or immunological tests on well-preserved soft tissues may yield evidence of infectious diseases. Paul Martin, professor emeritus of geosciences at the University of Arizona in Tucson, is the most vigorous proponent of the "overkill" theory. Because so many species of large American mammals disappeared about 11,000 years ago, he argues, over-hunting by the new arrivals is the most plausible explanation. There are abundant examples of extinction occurring soon after humans arrived on islands, apparently caused by hunting, and Martin believes the same thing could have happened continent-wide. "People can do it really fast and it won't leave much evidence behind," he said. The Clovis people "found a favorable environment. Their numbers would increase without serious limit, at a really rapid rate. Within 1,000 years, our species had swept through the Americas." But critics say that if Clovis hunters killed off the mammals, there should be more fossil evidence of the deed. Clovis people's stone weapon points have been found in association with mammoths, mastodons and bison but not with other mammals, noted Russell Graham, chief curator at the Denver Museum of Nature and Science.
Climate was probably paramount...
according to Graham, who presented new evidence to support his position last week at the Geological Society of America's annual meeting in Boston. "I would argue that [mammoths' and mastodons'] ranges were already collapsing" because of climate change when the Clovis hunters showed up, he said. "I think they would have gone extinct without people." Donald Grayson, an anthropology professor at the University of Washington, agrees. He points to recent archaeological evidence from Monte Verde, Chile, that humans had settled in the Americas about 13,000 years ago, well before the Clovis people arrived and the major wave of mammalian extinction occurred. Grayson said that at the end of the Ice Age, the melting of the glaciers that had covered Canada and the northern United States caused dramatic alterations in climate and vegetation.
according to Graham, who presented new evidence to support his position last week at the Geological Society of America's annual meeting in Boston. "I would argue that [mammoths' and mastodons'] ranges were already collapsing" because of climate change when the Clovis hunters showed up, he said. "I think they would have gone extinct without people." Donald Grayson, an anthropology professor at the University of Washington, agrees. He points to recent archaeological evidence from Monte Verde, Chile, that humans had settled in the Americas about 13,000 years ago, well before the Clovis people arrived and the major wave of mammalian extinction occurred. Grayson said that at the end of the Ice Age, the melting of the glaciers that had covered Canada and the northern United States caused dramatic alterations in climate and vegetation.
Above: An American Mastodon
In the continent's interior, the climate became more extreme.
Landscapes that had contained a patchwork of trees and pasture became more homogenous — either all forest or all grassland. "There were complex combinations of plants that you don't find after that period of time," he said. Many animals shifted their ranges in response to changing habitat. By constructing computer maps of the distribution of mammal fossils from different time periods, Graham sees evidence that the ranges of species like the Columbia mammoth and the Shasta ground sloth were steadily shrinking for thousands of years before they became extinct. "Large animals require larger geographic ranges, and as you reduce the geographic range, the probability of extinction goes up exponentially," he said. "With small distributions, local effects like fire, disease and competition become very important." But if climate change was severe enough to cause a wave of extinction in the Americas, it should have caused the same phenomenon globally, argues Ross MacPhee, curator of vertebrate zoology at New York's American Museum of Natural History. Yet most other regions were spared, even the nearby West Indies.
Landscapes that had contained a patchwork of trees and pasture became more homogenous — either all forest or all grassland. "There were complex combinations of plants that you don't find after that period of time," he said. Many animals shifted their ranges in response to changing habitat. By constructing computer maps of the distribution of mammal fossils from different time periods, Graham sees evidence that the ranges of species like the Columbia mammoth and the Shasta ground sloth were steadily shrinking for thousands of years before they became extinct. "Large animals require larger geographic ranges, and as you reduce the geographic range, the probability of extinction goes up exponentially," he said. "With small distributions, local effects like fire, disease and competition become very important." But if climate change was severe enough to cause a wave of extinction in the Americas, it should have caused the same phenomenon globally, argues Ross MacPhee, curator of vertebrate zoology at New York's American Museum of Natural History. Yet most other regions were spared, even the nearby West Indies.
Above: A Smilodon
"Why weren't things falling down in droves in Africa?" he asked.
Like Martin, MacPhee is struck by the fact that extinction in the Americas and several other places seems to have closely followed the arrival of humans. But he doubts that over-hunting is the explanation, noting that no whale or seal species has been driven to extinction in the past 200 years despite extreme over-hunting. Instead, MacPhee is betting that a virus or other microbe new to the Americas arrived with human settlers and killed off many mammal species that had no natural resistance. He points to the devastation caused later among Native Americans by smallpox, measles and other "European" infections. "Nothing in nature is able to cause such levels of havoc except emerging diseases," MacPhee said. "It was either the humans themselves that were vectors, or parasites of humans, or it could have been parasites of animals that came in with humans."To fulfill MacPhee's "hyperdisease hypothesis," a new infection would have had to spread quickly among individuals of all ages and sexes, and would have been able to cross species barriers. He suspects it would have spread through the air. Candidates might include influenza and rinderpest, a disease of cattle that also affects deer, antelope and related species. MacPhee is searching for evidence of such infections in frozen tissue from mammoths, ground sloths and other beasts that died out at the end of the Ice Age. An infected animal's immune system would make antibodies against the invading virus, chemicals that might be detectable. If antibody tests are positive, MacPhee plans to search for viral genetic material. "No extinction is a simple matter. There's always an environment in which it happens," said MacPhee. "I need to show and convince people that disease by itself could be considered a primary factor, rather than a secondary or negligible one."
Like Martin, MacPhee is struck by the fact that extinction in the Americas and several other places seems to have closely followed the arrival of humans. But he doubts that over-hunting is the explanation, noting that no whale or seal species has been driven to extinction in the past 200 years despite extreme over-hunting. Instead, MacPhee is betting that a virus or other microbe new to the Americas arrived with human settlers and killed off many mammal species that had no natural resistance. He points to the devastation caused later among Native Americans by smallpox, measles and other "European" infections. "Nothing in nature is able to cause such levels of havoc except emerging diseases," MacPhee said. "It was either the humans themselves that were vectors, or parasites of humans, or it could have been parasites of animals that came in with humans."To fulfill MacPhee's "hyperdisease hypothesis," a new infection would have had to spread quickly among individuals of all ages and sexes, and would have been able to cross species barriers. He suspects it would have spread through the air. Candidates might include influenza and rinderpest, a disease of cattle that also affects deer, antelope and related species. MacPhee is searching for evidence of such infections in frozen tissue from mammoths, ground sloths and other beasts that died out at the end of the Ice Age. An infected animal's immune system would make antibodies against the invading virus, chemicals that might be detectable. If antibody tests are positive, MacPhee plans to search for viral genetic material. "No extinction is a simple matter. There's always an environment in which it happens," said MacPhee. "I need to show and convince people that disease by itself could be considered a primary factor, rather than a secondary or negligible one."
The Pleistocene Era
The Pleistocene1.8 million to ~10,000 years agoThis mammoth, found in deposits in Russia, was one of the largest land mammals of the Pleistocene, the time period that spanned from 1.8 million to ~10,000 years ago. Pleistocene biotas were extremely close to modern ones — many genera and even species of Pleistocene conifers, mosses, flowering plants, insects, mollusks, birds, mammals, and others survive to this day. Yet the Pleistocene was also characterized by the presence of distinctive large land mammals and birds. Mammoths and their cousins the mastodons, longhorned bison, sabre-toothed cats, giant ground sloths, and many other large mammals characterized Pleistocene habitats in North America, Asia, and Europe. Native horses and camels galloped across the plains of North America. Great teratorn birds with 25-foot wingspans stalked prey. Around the end of the Pleistocene, all these creatures went extinct (the horses living in North America today are all descendants of animals brought from Europe in historic times).
It was during the Pleistocene that the most recent episodes of global cooling, or ice ages, took place. Much of the world's temperate zones were alternately covered by glaciers during cool periods and uncovered during the warmer interglacial periods when the glaciers retreated. Did this cause the Pleistocene extinctions? It doesn't seem likely; the large mammals of the Pleistocene weathered several climate shifts.
The Pleistocene also saw the evolution and expansion of our own species, Homo sapiens, and by the close of the Pleistocene, humans had spread through most of the world. According to a controversial theory, first proposed in the 1960s, human hunting around the close of the Pleistocene caused or contributed to the extinction of many of the Pleistocene large mammals. It is true that the extinction of large animals on different continents appears to correlate with the arrival of humans, but questions remain as to whether early human hunters were sufficiently numerous and technologically advanced to wipe out whole species. It has also been hypothesized that some disease wiped out species after species in the Pleistocene. The issue remains unsolved; perhaps the real cause of the Pleistocene extinction was a combination of these factors.
Many paleontologists study Pleistocene fossils in order to understand the climates of the past. The Pleistocene was not only a time during which climates and temperatures shifted dramatically; Pleistocene fossils are often abundant, well-preserved, and can be dated very precisely. Some, such as diatoms, foraminifera, and plant pollen, are both abundant and highly informative about paleoclimates. Today, there is concern about future climate change (e.g. global warming) and how it will affect us. Paleontologists who work on Pleistocene fossils are providing a growing amount of data on the effect of climate change on the Earth's biota, making it possible to understand the effects of future climate change.
It was during the Pleistocene that the most recent episodes of global cooling, or ice ages, took place. Much of the world's temperate zones were alternately covered by glaciers during cool periods and uncovered during the warmer interglacial periods when the glaciers retreated. Did this cause the Pleistocene extinctions? It doesn't seem likely; the large mammals of the Pleistocene weathered several climate shifts.
The Pleistocene also saw the evolution and expansion of our own species, Homo sapiens, and by the close of the Pleistocene, humans had spread through most of the world. According to a controversial theory, first proposed in the 1960s, human hunting around the close of the Pleistocene caused or contributed to the extinction of many of the Pleistocene large mammals. It is true that the extinction of large animals on different continents appears to correlate with the arrival of humans, but questions remain as to whether early human hunters were sufficiently numerous and technologically advanced to wipe out whole species. It has also been hypothesized that some disease wiped out species after species in the Pleistocene. The issue remains unsolved; perhaps the real cause of the Pleistocene extinction was a combination of these factors.
Many paleontologists study Pleistocene fossils in order to understand the climates of the past. The Pleistocene was not only a time during which climates and temperatures shifted dramatically; Pleistocene fossils are often abundant, well-preserved, and can be dated very precisely. Some, such as diatoms, foraminifera, and plant pollen, are both abundant and highly informative about paleoclimates. Today, there is concern about future climate change (e.g. global warming) and how it will affect us. Paleontologists who work on Pleistocene fossils are providing a growing amount of data on the effect of climate change on the Earth's biota, making it possible to understand the effects of future climate change.