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TOPIC: Homo Sapiens


L

Posts: 131433
Date:
Missing Link
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Fossil hunters in Ethiopia have unearthed an ancient skull, which they say could be a "missing link" between Homo erectus and modern people.

The cranium was found in two pieces and is believed by its discoverers to be between 500,000 and 250,000 years old.

The project's director, Dr Sileshi Semaw, said the fossilised specimen came from "a very significant time" in human evolutionary history.
It was found at Gawis in Ethiopia's north-eastern Afar region.
Stone tools and fossilised animals including two types of pigs, zebras, elephants, antelopes, cats, and rodents were also found at the site.
The face and cranium of the fossil are recognisably different from those of modern humans, but the specimen bears unmistakable anatomical evidence that it belongs to the modern human ancestral line.

Scientists conducting surveys in the Gawis River drainage basin found the skull in a small gully.
Gawis is situated near Hadar, where palaeoanthropologist Donald Johanson found the 3.2-million-year-old remains of "Lucy", the partial skeleton of a hominid belonging to the species Australopithecus afarensis, in 1974.

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L

Posts: 131433
Date:
RE: Homo Sapiens
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A new analysis of radiocarbon data shows that the ancestors of modern man moved into and across Europe faster than previously thought.

The process may only have taken 5,000 years to colonise Europe from Africa according to scientist Paul Mellars from Cambridge University.

"The same chronological pattern points to a substantially shorter period of chronological and demographic overlap between the earliest ... modern humans and the last survivors of the preceding Neanderthal populations" - Paul Mellars .

The reassessment is based on advances in eliminating modern carbon contamination from ancient bone fragments and recalibration of fluctuations in the pattern of the earth's original carbon 14 content.
Previously it was thought that this spread took place between 43,000 and 36,000 years ago, but the re-evaluated data suggests that it actually happened between 46,000 and 41,000 years ago.

"Evidently the native Neanderthal populations of Europe succumbed much more rapidly to competition from the expanding biologically and behaviourally modern populations than previous estimates have generally assumed" - Paul Mellars .

The invasion could have been helped by a major change in the climate which modern man would have been technologically and culturally better equipped to deal with than Neanderthals.

"There are increasing indications that over many areas of Europe, the final demise of the Neanderthal populations may have coincided with the sudden onset of very much colder and drier climatic conditions. This could have delivered the coup de grace to the Neanderthals in many parts of western and central Europe in their economic and demographic competition with the incoming modern groups" - Paul Mellars.

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L

Posts: 131433
Date:
Human Migration
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A new, more robust analysis of recently derived human gene trees by Alan R. Templeton, Ph.D, of Washington University in St Louis, shows three distinct major waves of human migration out of Africa instead of just two, and statistically refutes –strongly – the 'Out of Africa' replacement theory.

That theory holds that populations of Homo sapiens left Africa 100,000 years ago and wiped out existing populations of humans. Templeton has shown that the African populations interbred with the Eurasian populations – thus, making love, not war.

"The 'Out of Africa' replacement theory has always been a big controversy. I set up a null hypothesis and the program rejected that hypothesis using the new data with a probability level of 10 to the minus 17th. In science, you don't get any more conclusive than that. It says that the hypothesis of no interbreeding is so grossly incompatible with the data, that you can reject it" - Alan R. Templeton.

Templeton's analysis is considered to be the only definitive statistical test to refute the theory, dominant in human evolution science for more than two decades.

"Not only does the new analysis reject the theory, it demolishes it" - Alan R. Templeton.

Templeton published his results in the Yearbook of Physical Anthropology, 2005.
He used a computer program called GEODIS, which he created in 1995 and later modified with the help of David Posada, Ph.D., and Keith Crandall, Ph.D. at Brigham Young University, to determine genetic relationships among and within populations based on an examination of specific haplotypes, clusters of genes that are inherited as a unit.
In 2002, Templeton analysed ten different haplotype trees and performed phylogeographic analyses that reconstructed the history of the species through space and time.
Three years later, he had 25 regions to analyse and the data provided molecular evidence of a third migration, this one the oldest, back to 1.9 million years ago.

"This time frame corresponds extremely well with the fossil record, which shows Homo erectus expanding out of Africa then" - Alan R. Templeton.

Another novel find is that populations of Homo erectus in Eurasia had recurrent genetic interchange with African populations 1.5 million years ago, much earlier than previously thought, and that these populations persisted instead of going extinct, which some human evolution researchers thought had occurred. The new data confirm an expansion out of Africa to 700,000 years ago that was detected in the 2002 analysis.

"Both (the 1.9 million and 700,000 year) expansions coincide with recent paleoclimatic data that indicate periods of very high rainfall in eastern Africa, making what is now the Sahara Desert a savannah. That makes the timing very amenable for movements of large populations through the area" - Alan R. Templeton.

Templeton said that the fossil record indicates a significant change in brain size for modern humans at 700,000 years ago as well as the adaptation and expansion of a new stone tool culture first found in Africa and later at 700,000 years expanded throughout Eurasia.

"By the time you're done with this phase you can be 99 percent confident that there was recurrent genetic interchange between African and Eurasian populations. So the idea of pure, distinct races in humans does not exist. We humans don't have a tree relationship, rather a trellis. We 're intertwined"- Alan R. Templeton.

Source : Washington University in St. Louis

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L

Posts: 131433
Date:
Toba Supervolcano
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Toba is a supervolcano in the middle of the Indonesia island of Sumatra.
A large lake, 100km long and 30 km wide, now sits in the calderas.
the Dutch geologist van Bemmelen, in 1949, first found that Lake Toba was surrounded by a vast layer of ignimbrite rocks.
Later researchers found rhyolite ash similar to that in the ignimbrite around Toba in Malaysia and 3000 km away in India. The total amount of volcanic material ejected was found to be about 2,800 cubic kilometres.
The eruption may have release as much as 10^12 kg of sulphuric acid, an order of magnitude more than Laki in 1783 and Tambora in 1815, two of the greatest Holocene eruptions.
After the eruption, the magma chamber collapsed to form a caldera, which filled with water.


Location: 98°49'24" 2°34'54"

The Toba eruption was dated at 73,000 ± 4000 years ago. It had a Volcanic Explosivity Index of 8, making it the most recent eruption of a supervolcano and probably the greatest eruption in the last two million years.
Such a huge eruption probably lasted nearly two weeks. Very few plants or animals in Indonesia would have survived, and it is possible that the eruption caused a planet-wide die-off.
The Toba eruption led to a decrease in the average global temperatures by 3 to 3.5 degrees Celsius for several years. This massive environmental change is believed to have created population bottlenecks in the various human species that existed at the time
Geological evidence and computed models support the plausibility of a human catastrophe.
Genetic evidence based on mitochondrial DNA, suggests that all humans alive today are descended from a very small population, perhaps around 1,000 individuals. Using the average rates of genetic mutation, some geneticists have estimated that this population lived at a time coinciding with the Toba event.


Grey area Present-day topographic depression
Gold area Updomed areas
1 Sibandung caldera: made 73,000 years ago by the Toba YTT event (Young Toba Ash)
2 Haranggaol caldera: made 500,000 years ago by the Toba MTT event (Middle Toba Ash)
3 Sibandung caldera: made 800,000 years ago by the Toba OTT event (Old Toba Ash)


The MTT and OTT events were not as large as the YTT event of 73,000 years ago
but were still major eruptions of at least VEI 7.
V1 Tandukbenua (Sipisopiso) - young dacit-andesite volcano
V2 Pusubukit volcano - young dacit-andesite volcano
D1 Pardepur dacite domes
D2 Tuk-tuk rhyolite dome
HS Hot springs



Today, lake Toba is surrounded by two small, active volcanos as well as several updomed areas and hot springs. These features indicate that there is activity below the surface and that pressure is rising. Samosir island, too, is evidence for upthrust from below. Seismic readings indicate that two broad regions interpreted to be magma reservoirs lie below the depression.
The volcanoes Pusubukit and Pardepur, lie above the large southern chamber and each have roots that extends to mantle depths.

From the records it seems that Toba produces major eruptions every 300-400,000 years and that it will erupt again

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L

Posts: 131433
Date:
Homo Sapiens
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Scientists have identified a major climate crisis that struck Africa about 70,000 years ago and which may have changed the course of human history.


Tanganyika

The evidence comes from sediments drilled up from the beds of Lake Malawi and Tanganyika in East Africa, and from Lake Bosumtwi in Ghana.
It shows equatorial Africa experienced a prolonged period of drought.
It is possible, this was the reason some of the first humans left Africa to populate the globe.
Certainly, those who remained on the continent at that time would have had to be extremely resilient to make it through such hard times.

"This was a profound impact on the landscape. So it must have had a major impact, not just on humans but on all species in equatorial Africa at this time" - Christopher Scholz, Syracuse University, US.

Dr Scholz presented data from the drilling project here at the Fall Meeting of the American Geophysical Union.
The cores reveal that prior to 75,000 years ago, Lake Malawi, which is currently an inland sea some 550km long and 700m deep, was reduced to a couple of pools no more than 10km across and 200m deep.
Lake Bosumtwi, currently a 10km-wide lake that fills an old space impact crater, lost all of its water.

The 1.07 million year old Bosumtwi impact structure is surrounded by a circular depression and an outer ridge of diameter 20 km, and was caused by a 10^8 ton iron meteorite.

Only a prolonged continent-wide drought could have had this effect.

What makes the timing so fascinating is that it ties in with the "Eve hypothesis" of human evolution.
Genetic studies suggest modern humans are descended from a very small group, no bigger than 10,000 individuals who lived in East Africa at the time of this crisis.
Immediately after the drought ended, human populations started to expand rapidly - and many of our ancestors began moving out of Africa and into the Middle East, Asia and Europe.
Scientists are increasingly convinced that tragedies in the deep past have shaped human evolution.
The intriguing thought is that we owe our existence to a small band of survivors who clung on to life during a crisis of epic proportions or who simply decided they had to move to find water.

"We think there may be a connection between this climatic release - that is the rise in lake levels following this major desiccation event - and the order of magnitude increase in early modern humans. And, also, there may be a connection with the exodus of early modern humans out of Africa and this climatic release. There's been recognition that speciation of hominids is controlled by environmental factors - whether that's long-term changes in aridfication in Africa or perhaps the dramatic increase in variability in environmental conditions, such as in precipitation, temperature, and so forth" - Christopher Scholz.

So what caused the climate change?
A likely culprit is the Toba supervolcano in Indonesia that exploded 74,000 years ago.
Volcanic ash can affect the global climate. The fine ash and sulphur dioxide blasted into the stratosphere reflects solar radiation back into space and stops sunlight reaching the planet. This has a cooling effect on the Earth.

By comparing the amount of ash ejected by past volcanoes with their effect on the Earth's temperature, we can estimate the impact of the Toba eruption on the global climate .

"We can see this kind of plot predicts that the Toba eruption was so large that the temperature change after Toba in degrees Celsius would have been about a 5 degree global temperature drop, very significant, very severe global cooling. Five degrees globally would translate into 15 degrees or so of summer cooling in the temperate to high latitudes. The effects on agriculture, on the growth of plants, on life in the oceans would be catastrophic."

Lynn Jorde and Henry Harpending are scientists specialising in human genetics. By looking at mitochondrial DNA they noticed that there should be a wider range of genetic variation.

"Mutations in the mitochondria take place with clock like regularly, so the number of mutations give us a clock essentially that we can use to approximately date the major event. In the case of a population bottleneck we think that this would have occurred roughly 70-80,000 years ago, give or take some number of thousands of years. So then the real question is: what could have caused such a reduction, an extreme reduction, in the human population down to as few as 5 or 10,000 individuals?"

However, it should be noted that temperatures at other times during the last ice age fell far lower and did not come close to wiping out humankind; and the exact age of the bottleneck is poorly constrained so that linking it to the Toba eruption is speculative.

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