Showing posts with label genetic diversity. Show all posts

Thursday, 19 May 2016

Our Common Forefather: Just a Few Men Controlled Reproduction in Prehistory and Dominate World Genetics Today

Our Common Forefather

Just a Few Men Controlled Reproduction in Prehistory and Dominate World Genetics Today

Imaginative depiction of the Stone Age, by Viktor Vasnetsov. Source: Public Domain

A new genetic study of male ancestry shows there were periods in human prehistory when just a few elite men controlled reproduction. For example, one man about 190,000 years ago was the ancestor of 1,200 living men from 26 groups around the world whose genes were analyzed for the new study.

Who knows if that one man so long ago had great genes? Would the world have been different if it had been another man who had fathered much of the human race?

And one might also wonder just how many women this man had been with in his life. He lived at the dawn of the history of the Homo sapiens species, so perhaps just by dint of arithmetic and not necessarily by having many mates his genes came to dominate humanity.

But thousands of years later, genetic studies show, just a few men were responsible for much of the reproduction.

These tantalizing questions aren’t answered in the press release from the Wellcome Trust Sanger Institute reporting on a new study that found this ancient patriarch’s descendants are all over the world. Dr. Chris Tyler-Smith of the institute headed the study. An institute press release on the largest-ever study of the global genetic variation in the Y (male) chromosome states:

“The study … analysed sequence differences between the Y chromosomes of more than 1200 men from 26 populations around the world using data generated by the 1000 Genomes Project. Analysing the Y chromosomes of modern men can tell us about the lives of our ancestors. The Y chromosome is only passed from father to son and so is wholly linked to male characteristics and behaviours. The team used the data to build a tree of these 1200 Y chromosomes; it shows how they are all related to one another. As expected, they all descend from a single man who lived approximately 190,000 years ago.”

Another finding of the study is that one man who lived in Europe about 4,000 years ago is the ancestor of half of Western European men, Dr. Tyler-Smith told The Telegraph. “In Europe there was huge population expansion in just a few generations,” he told The Telegraph. “Genetics can’t tell us why it happened but we know that a tiny number of elite males were controlling reproduction and dominating the population. Half of the Western European population is descended from just one man.”

Time of haplogroup growth in different parts of the world.

World Map of Y-Chromosome Haplogroups - Dominant Haplogroups in Pre-Colonial Populations with Possible Migrations Routes. (CC BY SA 3.0)

Dr. Tyler-Smith says in the press release: “The best explanation is that they may have resulted from advances in technology that could be controlled by small groups of men. Wheeled transport, metal working and organised warfare are all candidate explanations that can now be investigated further.”

The study found an explosion in the population of males around 55,000 to 50,000 years ago in Asia and Europe and about 15,000 years ago in the Americas. Later rapid expansions of male populations happened in sub-Saharan Africa, Western Europe, South Asia, and East Asia between 8,000 and 4,000 years ago.

“The team believes the earlier population increases resulted from the first peopling by modern humans of vast continents, where plenty of resources were available,” the press release states.

Time of haplogroup growth in different parts of the world. (Wellcome Trust Sanger Institute)

Nearly a year ago scientists reported in the journal Nature that the majority of European men are descended from just a handful of Bronze Age male ancestors.

The presence of genetic material from just a few men in the Y chromosome sequence resulted from a population explosion several thousand years ago, researchers said. The team of scientists found that there was a huge increase in the population 2,000 to 4,000 years ago, in a band from Greece and the Balkans to the British Isles and Scandinavia.

The scientists in that study also speculated that perhaps cultural and technological changes were involved in the population explosions.

Bronze-Age warriors. (CC BY NC SA 2.0)

“The population expansion falls within the Bronze Age, which involved changes in burial practices, the spread of horse-riding and developments in weaponry. Dominant males linked with these cultures could be responsible for the Y chromosome patterns we see today,” Professor Mark Jobling of the University of Leicester said.

Most European Men are Descended from just Three Bronze Age Warlords, New Study Reveals

Bronze Age warriors on the lookout (Mike Bishop / Flickr)

The majority of European men are descended from just a handful of Bronze Age male ancestors, says a new genetic study in the journal Nature.

The presence of genetic material from just a few men in the Y chromosome sequence resulted from a population explosion several thousand years ago, researchers said. The team of scientists found that there was a huge increase in the population 2,000 to 4,000 years ago, in a band from Greece and the Balkans to the British Isles and Scandinavia.

Europe in the late bronze age of about 1100 BC. (Map by Xoil, Wikimedia Commons)

Popular Archaeology reported on the study, saying the researchers from the University of Leicester in England, headed by Professor Mark Jobling, determined the origin of DNA sequences of a big part of the Y chromosome in 334 men from 17 populations in Europe and the Middle East. They found three very young branches of DNA account for Y chromosomes of 64 percent of the men who gave genetic material for the study. The team used new methods for analyzing DNA variation to give a less biased picture of diversity and to give a better estimate of timing of population variations.

"The population expansion falls within the Bronze Age, which involved changes in burial practices, the spread of horse-riding and developments in weaponry. Dominant males linked with these cultures could be responsible for the Y chromosome patterns we see today,” Jobling told Popular Archaeology.

Research into Europeans' genetic heritage had previously focused on Old Stone Age (Paleolithic) or New Stone Age (Neolithic) ancestor-farmers of about 10,000 years ago.

The principal author of the study in Nature, Chiara Batini of the University of Leicester, said: "Given the cultural complexity of the Bronze Age, it's difficult to link a particular event to the population growth that we infer. But Y-chromosome DNA sequences from skeletal remains are becoming available, and this will help us to understand what happened, and when."

A finding by researchers from Harvard Univerity in Boston found in 2014 that the European population was descended from three tribes where there was intermarrying. This study too was in the journal Nature.

The BBC, reporting on the study, said the modern European gene pool developed from the three populations within the past 7,000 years.

“Blue-eyed, swarthy hunters mingled with brown-eyed, pale skinned farmers as the latter swept into Europe from the Near East. But another, mysterious population with Siberian affinities also contributed to the genetic landscape of the continent. ... Multiple lines of evidence suggested this new way of life was spread by a wave of migrants, who interbred with the indigenous European hunter-gatherers they encountered on the way,” the BBC wrote.

The study found humans arrived in Europe about 45,000 years ago. These people were replaced by others who arrived from the Near East and the Levant about 7,000 years ago, researchers who examined ancient and modern DNA found. Researches from Harvard found most modern Europeans have a mixture of early European farmer DNA, western European hunter-gatherer DNA and some northern Eurasian ancestry.

For this study the researchers studied DNA in ancient bones of seven Scandinavian hunter-gatherers, one from Luxembourg and an ancient farmer from the area of Stuttgart, Germany and compared it to the genomes of 2,000 modern people around the world. So this was different than the more recent study by the University of Leicester, which examined just modern DNA of living men.

From Ancient Origins @ http://www.ancient-origins.net/news-evolution-human-origins/just-few-men-controlled-reproduction-prehistory-and-dominate-world-020821?nopaging=1#sthash.oCzKaQxQ.dpuf and http://www.ancient-origins.net/news-evolution-human-origins/most-european-men-are-descended-just-three-bronze-age-warlords-new-020361?nopaging=1#sthash.qTvxcVBJ.dpuf

For more hidden history see http://nexusilluminati.blogspot.com/search/label/hidden%20history

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Wednesday, 23 September 2015

Humans LOST DNA as they evolved: Early species had the equivalent of thousands more genes than we do now

Humans LOST DNA as they evolved:

Early species had the equivalent of thousands more genes than we do now

Early human species are thought to have lost DNA as they migrated around the globe and their populations became constrained. Neanderthals, like the one illustrated above, and Denisovans had around 104,000 base pairs in their DNA that are now abscent from the genomes of modern humans

Geneticists analysed the DNA of 125 human populations around the world
They then estimated how much DNA has been lost since we split from apes
They calculated humans have lost 40.7 million base pairs as we evolved
The study also found large segments of DNA from an extinct early human species called Denisovans in the genomes of people from south Pacific

By Richard Gray

Humankind likes to believe it sits at the top of the evolutionary tree because of its complexity, but our success may be down to us actually losing some of our DNA.

Geneticists have discovered that modern humans actually possess far less genetic information in our cells than their ancestral cousins. They estimate since early humans split from the common ancestor we shared with our closest living relatives, chimpanzees, we have lost 40.7 million base pairs.

Scientists have created the most detailed map of human genetic diversity by sampling DNA from 125 populations round the world, shown on the map above. They found indigenous people from the South Pacific had a high levels of a section of DNA from an extinct human species, the Deniosvans, shown by the pies above

These basic biochemical units are what make up DNA strands and group together to encode genes.

Researchers say around half of these genetic sequences appear to have been repeated sections of DNA, but 27.96 million base pairs lost were unique.

This could have been the equivalent of thousands of genes, although much of the DNA could have had no function.

HUMANS HAVE 'PRIMATIVE' HANDS

Humans like to think of themselves as the peak of the evolutionary tree, honed by millions of years of evolution that sets us apart from our closest animal cousins.

But research suggests one part of our body – our hands – are actually more primitive than those of chimpanzees.

Analysis of the anatomy of the hands of living and extinct apes has revealed that human hands have actually evolved little since we shared a common ancestor with chimpanzees.

Chimps by contrast have developed elongated fingers to help make them better suited to life in the trees.

Human hands have retained their relatively long thumbs in relation to their index fingers, making them much more similar to the appendages of gorillas.

The dexterity of the human hand has long been believed to be what sets us apart from our animal cousins and lies behind our success as a species.

It was also long thought that our use of tools was partly responsible for our unique hands.

The new findings, however, suggest the proportions of the human hand appears to have been in place long before we separated from chimpanzees and bonobos, from the genus Pan, around five million years ago.

By analysing the DNA of 125 human populations around the world, the scientists have produced the most detailed map of human genetic diversity yet produced.

They found humans appear to have lost around 15.8 million base pairs after separating from apes early in our evolutionary history in Africa, around 13 million years ago.

As humans then dispersed and spread around the world, they shed a further 12.16 million unique pieces of DNA.

This suggests trimming down sections of DNA have been just as important in human evolution as the reordering and development of new genes has.

Writing in the journal Science, the researchers, led by Professor Evan Eichler, a geneticist at the University of Washington in Seattle, said dramatic losses in human population after leaving Africa played a role in the loss of much of this DNA.

They said: 'The breadth of the dataset allowed us to reconstruct the structure and content of the ancestral human genome prior to human migration and subsequent gene loss.

'As expected, Africans were more likely to show evidence of these ancestral sequences compared to non-African populations, as the latter have experienced more population bottlenecks and thus retained less of the ancestral human diversity.'

The human genome has around three billion base pairs, which reside in 23 chromosomes in the heart of almost every cell in our body.

The average gene in the human genome is around 765 base pairs long, meaning humans could have lost the equivalent of up to 37,000 genes since splitting from our ape cousins.

The international team of researchers, from 39 different institutes, analysed the DNA of 236 people from 125 different human populations.

They then compared these to the geneomes from chimpanzees, organgutans and ancient human species like the Neanderthals and Denisovans.

Their results have helped to highlight the complexity of human migration around the world, as our ancestors at times interbred with other human species or were forced to indulge in inbreeding.

The map above shows the 125 populations sampled by the researchers for the study and how they relate to each other, as illustrated by the coloured markers

The researchers found a segment of DNA in the genome of Denisovans that is duplicated (shown left) and this appears to have occurred around 440,000 years ago before interbreeding occurred with modern humans in Oceanic populations that are indigenous to the South Pacific islands

They focused particularly on sections of DNA known as 'copy number variants' – alterations which lead to a variation in the number of copies of DNA sections.

They found there were large duplicated segment of DNA from the extinct Denisovans can now be found in Oceanic populations, such as the islands of the South Pacific.

This suggests there was a period of intense interbreeding between the Denisovans and modern humans around 40,000 years ago.

The researchers estimate that the duplicated segment of DNA, which is found in the Denisovan chromosome 16, occured around 440,000 years ago.

They found Neanderthals and Denisovans had around 104,000 base pairs in their genomes that are not found in modern humans.

However, modern humans have around 33,300 base pairs not found in Neanderthals or Denisovans, suggesting these extinct species had also lost significant portions of DNA.

This genetic tree shows the relationships between different human populations according to the deletions found in their genomes. The extinct Neandethals and Denisovans sit far out on their own, as shown above

Studying these differences could also help to provide clues to how modern humans managed to survive and flourish while other species of human died out.

Surprisingly, the results also suggest that DNA deletions are more reflective of selection in our evolutionary history, whereas duplications of DNA sequences highlight genetic subpopulations.

Writing in the journal, the researchers said: 'Both deletion and duplication analyses consistently distinguish African, Oceanic, and Amerindian human populations.

'Africans show the greatest deletion and duplication diversity and have the lowest rate of fixed deletions with respect to ancestral human insertion sequences.

'Oceanic and Amerindian, in contrast, show greater copy number variation differentiation, likely as a result of longer periods of genetic isolation and founder effects.

'Among the Oceanic, the Papuan–Bougainville group stands out in sharing more derived copy number variation alleles (genes) in common with Denisova, including a massive interspersed duplication that rose to high frequency over a short period of time.'

The researchers found we have lost around 40.7 million base pairs from our genomes since early human ancestors split from apes around 13 million years ago.

See : Global diversity, population stratification, and selection of human copy number variation

From the Daily Mail @ http://www.dailymail.co.uk/sciencetech/article-3187857/Humans-LOST-DNA-evolved-Early-species-equivalent-thousands-genes-now.html

For more information about (terrestrial) human origins see http://nexusilluminati.blogspot.com/search/label/human%20origins