Skip to comments.Debate Heats Up On Role Of Climate In Human Evolution
Posted on 11/03/2003 7:52:15 PM PST by blam
Contact: Ann Cairns
Geological Society of America
Debate heats up on role of climate in human evolution
Boulder, Colo.- Scientists at the Geological Society of America annual meeting in Seattle next week are taking a comprehensive new look at drivers of human evolution. It now appears that climate variability during the Plio-Pleistocene (approximately 6 million years in duration) played a hugely important role. Astronomically controlled climate forcing on scales ranging from 20,000 to 100,000 years down to El Niños (5-7 years) made a highly unpredictable environment in which generalists with intelligence, language, and creativity were best able to adapt. Traditional studies of human evolution have focused largely on finding and dating hominid fossils. Today the investigation is rapidly expanding with advances in DNA research and understanding of global climate change. The combination of archeological, geologic, and paleoclimatic evidence allows scientists to explore such tantalizing questions as:
What were the drivers that may have nudged hominids toward bi-pedalism? Why did only one species ultimately succeed at it? How might global climate change have influenced brain development, development of tools, and the exodus from Africa? How did glacial periods in Europe, Asia, and North America impact humans? "The answers to these questions will not all come from the bones, but from what was taking place in the environment in which they were found," says Gail Ashley, Dept. of Geological Sciences, Rutgers University.
Ashley and Craig Feibel of Rutgers have assembled an interdisciplinary group of distinguished scientists physical anthropologists, archaeologists, geologists, and paleoclimatologists for a Pardee Keynote Symposia, The Paleoenvironmental and Paleoclimatic Framework of Human Evolution. The symposium takes place at GSA on Monday, Nov. 3.
William Ruddiman, celebrated author of Earth's Climate: Past and Future, provides an overview of climate change over the last several million years, helping to separate fact from fiction.
Bernard Wood, a world-renowned physical anthropologist, discusses the hominin family "Tree of Life" and the challenges of working with the meager fossil record of human evolution spanning the last 7 million years.
Thure Cerling is a pioneer in using isotope records of bones and teeth. With co-authors Meave Leakey and John Harris he provides a comprehensive look at the impact of climate change on the biological record from one of richest fossil sites in the world (Lake Tukana, Kenya).
Jonathan Wynn unravels some of the paleoclimate puzzles from fossil soils at key sites in the "Cradle of Mankind" in East Africa. The soils provide clear documentation of extremely arid events. Prolonged droughts may have been a factor in triggering migrations of hominins out of Africa.
Julia Lee-Thorpe, a trail blazing geochemist, has taken a more personal approach to human evolution by examining hominin nutrition through analyses of tooth enamel. Diet is a direct record of available food resources and an indirect record of the environment in which the individual lived.
Andrew Hill, a globally recognized expert on the paleontological record in East Africa, reports on the latest findings from the superb paleoenvironmental record of the Tugen Hills, Kenya (site of the discovery of the 6 million-year-old "Millennium Man").
Gail Ashley speculates on the critical role of the availability of water in affecting human evolution, based on studies from Olduvai Gorge and other fossil localities. Dramatic fluctuations in climate (wet to dry) in East Africa may have been an important factor in affecting natural selection of species able to cope through arid periods.
David Lordkipanidze and Reid Ferring tell an exciting chapter on the "Out-of-Africa" story from Dmanisi, Republic of Georgia. The 1.8 million-year-old hominin remains are the first discoveries outside Africa to show clear affinities to early African Homo.
Rick Potts, author of the provocative book Humanity's Descent: The Consequences of Ecological Instability, contributes important new findings from China revealing the successful adaption of some hominin groups 400,000 years ago to climatic fluctuations and drastic environmental change.
James Dixon, a recognized authority on peopling of the Americas, provides the most recent chapter in the record of humans. Continental ice sheets, sea level changes and the presence of the Bering land bridge effectively controlled immigration from Asia to the New World.
Craig Feibel provides perspective on the physical environmental constraints in which human evolution took place. He examines the role of geologic factors such as plate tectonics, sea level change, and climate fluctuations in affecting selective pressure on hominins and thereby impacting how and where humans evolved. The Paleoenvironmental and Paleoclimatic Framework of Human Evolution Monday, Nov. 3, 8:00 a.m.-12:00 p.m., WSCTC Ballroom 6B
During the GSA Annual Meeting, Nov. 2-5, contact Ann Cairns at the GSA Newsroom, Washington State Convention Center and Trade Center, Seattle, for assistance and to arrange for interviews: 206-219-4615.
Geological Society of America 115th Annual Meeting Nov. 2-5, 2003 Washington State Convention and Trade Center Seattle, WA, USA
Geological Society of America www.geosociety.org
Yes it could. Which group do I ping? Both?
I agree. I think the cold taught us how to plan and have a concept of the future. Those who didn't plan when things were good(warm), didn't survive when things were bad(cold).
Gods, Graves, Glyphs
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Keep that up and we'll make an anthropologist outta you.
Evolution is not science, it is the ignorant religion of the God haters. Objective science proves that creation is undeniable fact.
Nah, that's archaeology. Anthropologists mostly think about what archaeologists find.
My mother used to sing that song to me when I was young.
Evolution is science. Biologists refer to human evolution frequently. Christians who understand biology don't have a problem with this theory.
It is those folks who demand that science be curtailed are the God-haters. I know you don't have a dinosaur in your basement, or are in possession of a 12 billion year-old human fossil.
However, I agree that creation is a fact.
Or, you planned and lived with it. The cold is also why we have white people...vitamin 'D' and all.
I have edited your post for clarity.
The theory was that a long time ago, there was no Isthmus of Panama, and some ocean current flowed through the gap between North and South America from the Atlantic to the Pacific Ocean.
When the Isthmus of Panama rose from the sea, this current was deflected back into the Atlantic, toward Africa. As a result, Africa became cooler and more humid, somehow favoring the rise of homo sapiens.
I think that was in the millions of years ago...not positive though. (I would like to know if you find out for sure...I could work with that, lol)
That's going to come as a big surprise to the scientists who publish and submit articles to scientific journals such as:
...or those scientists who publish such papers as:
Tracing the LINEs of human evolution (Igor Ovchinnikov, Adrienne Rubin, and Gary D. Swergold) [Excellent paper]And so on and so on.
Alu Insertion Polymorphisms and Human Evolution: Evidence for a Larger Population Size in Africa (Mark Stoneking, Jennifer J. Fontius, Stephanie L. Clifford, Himla Soodyall, Santosh S. Arcot, Nilmani Saha, Trefor Jenkins, Mohammad A. Tahir, Prescott L. Deininger, and Mark A. Batzer)
Evolution is not science,
Of course it is, but you're welcome to try to offer an argument why you think it isn't, if you actually have one.
it is the ignorant religion of the God haters.
That's going to come as a big surprise to the millions of Christians who accept evolution.
Objective science proves that creation is undeniable fact.
Ooh, this ought to be interesting -- why don't you provide us some specific examples of the "objective science" which "proves" that creation is an "undeniable fact"?
See any book by Elaine Goodman, The Aquatic Ape, Descent from Woman, etc.
Conversely, in extant primitive societies there hasn't been the environmental pressure over time to enforce change. Their technology required few tweakings and cultural practices remained essentially static.
It seems to me that we've discussed this before.
By Kathy A. Svitil
DISCOVER Vol. 17 No. 04 | April 1996 | Ancient Life
When the Isthmus of Panama rose from the sea, it may have changed the climate of Africa--and encouraged the evolution of humans.
The emergence of the Isthmus of Panama has been credited with many milestones in Earths history. When it rose from the sea some 3 million years ago, the isthmus provided a bridge for the migration of animals between North and South America, forever changing the fauna of both continents. It also blocked a current that once flowed west from Africa to Asia, diverting it northward to strengthen the Gulf Stream. Now Steven Stanley, a paleobiologist at Johns Hopkins, says that that change in currents may be behind yet another major event: the evolution of humans. When the isthmus rearranged the ocean, he says, it triggered a series of ice ages that in turn had a crucial impact on the evolution of hominids in Africa.
Stanleys hypothesis, which he describes in a new book called Children of the Ice Age, is based on ideas developed by a number of oceanographers over the past decade, notably Wallace Broecker of the Lamont-Doherty Earth Observatory. Broecker has called attention to the climatological implications of a fundamental difference between the Atlantic and the Pacific: the Atlantic is much saltier. The difference arises in part because of the dry trade winds that blow west off the Sahara Desert, evaporating water off the ocean and leaving salt behind. The trade winds are thirsty, and they pick up a lot of moisture from the Atlantic, says Stanley. Much of that moisture is carried over into the Pacific and drops into the ocean. So the salinity is quite low on the Pacific side of the Isthmus of Panama, but very high on the Atlantic side.
The result is a global system of ocean currents called the conveyor belt. As salty water moves north in the Atlantic--carried by the Gulf Stream, for instance--it gets colder. The combination of extra saltiness and cold temperatures makes the water especially dense--and especially prone to sinking. In the vicinity of Iceland the salty water sinks to the ocean floor. From there it spreads southward to Antarctica, converges with another sinking current, and loops through the Indian Ocean and into the Pacific. There the water wells back up to the surface and slowly returns to the Atlantic around the tips of South America and Africa.
The entire conveyor belt, the theory goes, is driven by the sinking of water in the Atlantic, and ultimately by the salinity difference between the Atlantic and the Pacific. (The water of the North Pacific gets just as cold as the Atlantic in winter, Stanley says, but it doesnt sink, because the Pacific is less salty, and therefore more buoyant.) And before the Isthmus of Panama formed, Stanley argues, the conveyor belt didnt exist. Atlantic water flowed directly into the Pacific between the Americas, reducing the salinity difference. The water that then flowed into the North Atlantic, however, wasnt salty enough to sink into the deep ocean; instead it continued northward to the Arctic. Therein lies the key, in Stanleys view, to how the isthmus may have affected human evolution.
As long as North Atlantic waters flowed into the Arctic, he says, they kept it relatively warm--warm enough, for instance, that marine species from temperate climes, like the blue mussel, could use the Arctic to migrate from the Pacific to the Atlantic. After the isthmus formed, however, the conveyor belt denied the Arctic those warm waters, and because the sun strikes at such a low angle up there, Stanley says, it got very cold. Pack ice soon formed, which reflected the suns rays, chilling the region still further. Soon the influence of the frigid north spread inexorably south, as did the glaciers, and the Ice Age began--a long period of waxing and waning ice sheets from which we have yet to emerge.
The impact of the Ice Age was most strongly felt in the higher latitudes, but it also made Africa colder, windier, and drier. Many researchers have suspected that these changes spurred the evolution of Australopithecus, the earliest hominid. As Africa cooled and dried, this school of thought contends, the habitat of Australopithecus changed. Before the Ice Age began, there was probably a very broad zone of open forests on the fringe of the rain forest that was accessible to Australopithecus, Stanley says. When the world cooled off, however, the rain forest shrank, while desert and grassland regions expanded. Thats a big problem if youre an australopithecine living a semiarboreal life in a forest habitat. It must have been a tremendous crisis, Stanley says. Australopithecus had to survive on the ground and evolve mechanisms that would allow it to do so. Sometime after 3 million years ago, it branched into two lineages--strong-jawed Paranthropus and big-brained Homo.
As it happens, there is now strong evidence linking that evolutionary split to a climate change in Africa. The evidence was reported last year by paleoclimatologist Peter deMenocal of Lamont-Doherty, who studied marine sediment cores drilled off the African coast. The cores contain dust blown off the neighboring continent, so they provide a record of how dry it was there when each layer of sediment was laid down--a colder, drier climate made for more dust. Over the past few million years, the African climate has oscillated continually between periods that were relatively cold and dry and ones that were warmer and wetter. But around 2.8 million years ago, the sediment cores show a pronounced change. The duration of the cold-warm cycles increased, from an average of around 23,000 years to 41,000 years. And judging from the increased amount of dust in the sediment, the cold periods got markedly colder and drier.
Whats more, says deMenocal, the sediment cores show the same chilling effect two more times in African history--and each time coinciding with a milestone in human evolution. The next change happened 1.7 million years ago--just about when Homo erectus, a direct ancestor of humans, appeared. The colds got colder, the winds got windier, and the dries got drier, says deMenocal. And then 1 million years ago the duration of these events became longer again--100,000 years instead of 41,000 years--while the colds got colder still, and the dries even drier. At around that time Paranthropus, presumably unable to survive a more hostile environment, died out, leaving the field to Homo erectus.
The lengths of the individual cold-warm cycles in Africa reflect the influence on Earths climate of another factor besides the oceanic conveyor belt--the periodic changes in the orientations of Earths axis that are known as Milankovitch cycles. The axis wobbles like a tops, tracing out a circle against the stars every 23,000 years; meanwhile the angle at which it is tilted from the vertical oscillates every 41,000 years, from 21.5 degrees to 24.5 degrees and back. (Right now it is 23.5 degrees.)
DeMenocals sediment cores suggest that 2.8 million years ago, the tilt cycle took over dominance of the African climate from the wobble cycle--and made the climate more extreme. When the tilt angle is low, less sunlight hits the high latitudes of the Northern Hemisphere in summer, less ice melts, and ice sheets expand. That is just what Stanley says happened when the Isthmus of Panama formed and ocean currents stopped warming the Arctic.
The rise of the isthmus, says Stanley, may have made Earth more susceptible to the tilt cycle and may have conspired with it to allow ice sheets to spread over the Northern Hemisphere. The effects of those ice sheets were soon felt in Africa. Its a jolting notion of how the human genus evolved, Stanley says. The uplift of this skinny little neck of land between the Americas set in motion an enormous oceanographic change that allowed the Arctic to cool; that had an enormous effect in Africa, by drying the climate and leading to the evolution of Homo. In other words, we would not exist if this little neck of land had not risen up across the ocean from where our ancestors lived.
Calling something science does not make it science (perhaps 'orwellian science')
If the ancient Egyptians had not been conquered from the outside, their lifestyle and belief systems would probably have gone unchanged for millennia as long as the Nile continued to inundate.
You check out history.
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