The Human Population Explosion 40,000 Years Ago --New Theories on Why (Today's Most Popular)
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March 11, 2013

The Human Population Explosion 40,000 Years Ago --New Theories on Why (Today's Most Popular)

 

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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. Research completed in fall of 2012 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," said 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 DNAinformation 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," said 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?"

For more information: Genome Res. 2012 doi:10.1101/gr.143198.112 Journal reference: Genome Research

The Daily Galaxy via Wellcome Trust Sanger Institute

Image credit: With thanks to bbc.co.uk

Comments

If every person has two parents, and then four grandparents, and then eight grandparents, etc. It is almost incomprehensible what the human population would have been just thirty or forty thousand years ago!

I wonder why the common belief is that everything emerged from Africa, since on the rest of the continents had the same conditions ?!

It took them tens of thousands of years to adapt to the mountainous, forested surroundings on the inner continents.

Epigenetics put a lie to this time-dependent adaptation.
time of first expansion: Neanders: 200,000 ya
time of second expansion: CroMagnon 100,000 ya
during this 100,000 span between the Neanders are faulted due to lack of innovation, which, it is claimed, the CroMagnon had.
50,000 ya show massive intellectual advance everywhere.
Why is it surprising to see fertility rocket?

There was a very significant archaeological event. 40,000 years ago we first start to see spear heads, sowing needles, fish hooks and fishing nets. People lived near the water. They followed the rivers like the Yellow River in China and the Euphrates River in Mesopotamia. These were the cradle of civilizations. This is where the Neanderthals went extinct and the Modern Humans exploded. You can find artifacts up to 300 miles from where they were made.

Life lives by itself. Humans reproduced following their own lusts, their own desires, freely, in a constant fight for resources, better partners, and so on. It was a constant adventure to live in this world. Much different environment we see today...


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