Posted on 10/31/2012 1:10:13 AM PDT by LibWhacker
DNA sequencing of 36 complete Y chromosomes has uncovered a previously unknown population explosion that occurred 40 to 50 thousand years ago, between the first expansion of modern humans out of Africa 60 to 70 thousand years ago and the Neolithic expansions of people in several parts of the world starting 10 thousand years ago. This is the first time researchers have used the information from large-scale DNA sequencing to create an accurate family tree of the Y chromosome, from which the inferences about human population history could be made.
"We have always considered the expansion of humans out of Africa as being the largest population expansion of modern humans, but our research questions this theory," says Ms Wei Wei, first author from the Wellcome Trust Sanger Institute and the West China University of Medical Sciences. "The out-of-Africa expansion, which happened approximately 60,000 years ago, was extremely large in geographical terms with humans spreading around the globe. Now we've found a second wave of expansion that is much larger in terms of human population growth and occurred over a very short period, somewhere between 40,000 to 50,000 years ago."
There is no obvious archaeological event that would explain why this sudden expansion in the human population occurred. One possible theory is that during the original out-of-Africa expansion, humans moved along the coastlines of the world, settling as they went. Their origins and genetic makeup would mean that these people were suited to coastal life, but not to the demands of living inland. This would have prevented large population growth as the coasts could only sustain a certain number of people.
"We think this second, previously unknown population boom, may have occurred as humans adapted to their new environment after the first out-of-Africa expansion," says Dr Qasim Ayub, lead author from the Wellcome Trust Sanger institute. "We think that when humans moved from the horn of Africa to Asia, Australia and eventually Europe, they remained in small groups by the coasts. It took them tens of thousands of years to adapt to the mountainous, forested surroundings on the inner continents.
However, once their genetic makeup was suited to these new environments, the population increased extremely rapidly as the groups travelled inland and took advantage of the abundance of space and food." The work highlights how it is now possible to obtain new biological insights from existing DNA sequencing data sets, and the value of sharing data. The majority of the DNA information used for this study was obtained from freely-available online data-sets.
Since the Y chromosome is found only in men, its history and evolution are easy to study and interpret. This study also highlights how information generated by other genetic studies, in this case by the company Complete Genomics, can be used to investigate human genetic archaeology. The lengths between the branches and the length of each branch on the Y chromosome family tree provide insights into the evolution of the human population. The closer the branches are, the more rapidly the population was expanding and separating, most likely into different geographic areas. The longer the branch length, the greater the time that group of people have been separated from the other groups.
"We have provided a nearly ten-fold increase in the number of genetic markers found on Y chromosomes and discovered new historical insights into the evolution of modern humans using DNA sequencing information from just 36 men," says Dr Chris Tyler-Smith, lead author from the Wellcome Trust Sanger Institute. "We now want to look at ten times this number of Y chromosomes in data from the 1000 Genomes Project. Who knows what we will find then?"
Most major cities and most of the world's population still lives along the coasts.
It could be something as simple as the development of improved hide tanning methods and better shoes.
I know that may seem a stretch, but new horizons become available to those who adapt, and the most simple seeming technologies often make that possible.
Walmart ran out of $9 birth control?
From memory:
1) "domesticated dogs" were present about 100,000 years ago
2) A population bust—which left only 10,000 humans—occurred around the time of this population "explosion".
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| GGG managers are SunkenCiv, StayAt HomeMother & Ernest_at_the_Beach | |
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Thanks LibWhacker.[snip] DNA sequencing of 36 complete Y chromosomes has uncovered a previously unknown population explosion that occurred 40 to 50 thousand years ago, between the first expansion of modern humans out of Africa 60 to 70 thousand years ago and the Neolithic expansions of people in several parts of the world starting 10 thousand years ago. This is the first time researchers have used the information from large-scale DNA sequencing to create an accurate family tree of the Y chromosome, from which the inferences about human population history could be made. [/snip]That entire paragraph is nonsense -- there isn't any way to show temporal origin using DNA, just as it isn't possible to show ancient geographic origins using DNA. |
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The “bust” happened around 70,000 years ago, because of the explosion of the Toba supervolcano in Indonesia. The “boom” was 30,000 years later. 40,000 years ago probably correlates with the invention of boats/rafts (opening up the interiors of continents via rivers) and maybe improvements in hunting technology.
I'll put my money on some sort of climate warming.
Couldn’t have been rafts, more people would have survived the flood...
Genetic makeup doesn't change. Either they were homo sapiens or they weren't. Adaptation to a new environment does not require genetic change.
He doesn’t figure into population, he only has one child, and no known desire for the kind of sex that produces children.
Environmental differences are the most likely explanation for genetic diversity between populations adapted for different geographic areas.
Populations from Norway are not light skinned for fun, but because of the absolute necessity of capturing sunlight on the skin (instead of filtering it out) in order to synthesize vitamin D.
But their (Norwegians) genetic makeup did not change. Those who were fairer skinned performed better so they had more and healthier children (and thus the population as a whole became more fair skinned).
Some random population didn’t just grow a new gene for fair skin. That capability was always there in the dna. Their genetic makeup did not change. (see what I mean?)
Any allele that led to lighter skin already in the population was favored and increased in frequency within the population - that IS a change in the genetic makeup of the population. ( for example: A herd of cattle where only one in one hundred is red color has a different genetic makeup from a herd of cattle where 75 out of a hundred are red color - even if the gene for red color is the same in both herds)
Any spontaneous mutation that disabled genes that would lead to very dark skin was favored and much more likely to become ‘fixed’ in the population and even to achieve near universal ‘penetrance’.
And that is just skin color.
There are also changes in lanky/stocky - those from equatorial climes tend to be lanky and those from polar climes tend to be stocky.
There are changes in lactose tolerance - people from Northern Europe and some African tribes have (different) mutations in the region that would otherwise shut down the gene for lactase (the enzyme that digests lactose) after infancy.
The noses of Africans tend to be wide to better get rid of heat.
The noses of Europeans tend to be narrow to better conserve heat.
Etc, etc, etc.
All of those constitute a change/difference in genetic makeup of populations.
I always thought it was the invention of new technologies.
Using an atlatl a man can chunk a dart 100 yards or so. Add a poison, e.g., aconite from monkshood flowers and you can kill megafauna such as mammoths, giant sloths, sabertooth tigers, etc.
With an easy, plentiful food source people could multiply rapidly as they ranged farther and farther to find new herds.
That’s why the megafauna died out while smaller, more nimble game, e.g., deer, survived. Atlatls are not accurate enough to kill deer at long range.
The way it is phrased the author is saying that people evolved to adapt to that environment. They did not. Those who were already more capable (that is, those who already had the preferred genetic code for that environment prospered while the other didn't. Mankind did not evolve, the capability for those environments was there from the start.)
First that IS a genetic change in a population, and second it is only half of the equation. New and useful variations arise in populations all the time. Lactose tolerance for example.
NO it is not a genetic change. it is a change in the preponderance (sorry but I can’t think of the proper word for it right now) of a gene which was always present in the general population. The genes did not change, there was no evolution.
My whole point here is that the human genome already contained all the genetic variation required to adapt to any place on earth.
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