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05-30-2018, 08:08 PM
Generations of brutal wars between ancient clans caused a global COLLAPSE in the genetic diversity of men 7,000 years ago, say scientists
From around 7,000 years ago, something strange seems to have happened to men. Genetic records show that their diversity appeared to have collapsed entirely, and stayed that way for the next 2,000 years. So extreme was the collapse in the Y chromosome that it was as if there were only one man left to mate for every 17 women.
Now scientists think they know why. According to researchers at Stanford University, the collapse was the result of generations of war between clans, whose membership is determined by male ancestors. Pictured is a skeleton from 7,500 BC
Neolithic remains across Europe show tribes likely engaged in violent assaults involving clubs, axes, and arrows about 5,500 years ago.
The 'Neolithic Y-chromosome bottleneck' marks a time when human genetic diversity took a dramatic nosedive.
The slaughter was so severe the male population was decimated to one-twentieth of its original level.
However, by looking at genetic patterns in modern humans, researchers found that the decline was observed only in men - specifically on the Y chromosome, which fathers pass on to their sons.
'An abrupt population bottleneck specific to human males has been inferred across several Old World (Africa, Europe, Asia) populations 5000–7000 BP', researchers, led by Tian Chen Zeng, a Stanford undergraduate in sociology, wrote in their paper published in Nature.
This suggested large numbers of men were dying before having sex and producing children which led researchers to suggest it could a result of generations of warfare.
The team also thought the genetic bottleneck might have been compounded by changing social structures - specifically the creation of patrilineal clans.
After the onset of farming and herding around 12,000 years ago, societies grew increasingly organised around extended kinship groups, which were largely patrilineal.
This cultural fact has potentially significant biological consequences as it is key how clan members are related to each other.
While women may have married into a clan, men in such clans are all related through male ancestors.
This meant they tended to have the same Y chromosomes.
Researchers point out that if there are wars between the clans and wars repeatedly wiped out entire clans over time, they could also wipe out a good many male lineages and their unique Y chromosomes in the process.
This would therefore greatly reduce overall diversity.
The team looked at DNA patterns in modern humans, and their study did not touch on the methods of war that may have driven the Neolithic bottleneck.
http://i.dailymail.co.uk/i/pix/2018/01/23/15/48803F0D00000578-5302565-image-a-6_1516719977902.jpg
The Y chromosome is one of the sex chromosomes in animals and is responsible for the sex determination of unborn offspring. Previous research has suggested the Y chromosome has just 4.6 million years before it completely disappears
This may sound like a long time, but it isn't when you consider that life has existed on Earth for 3.5 billion years.
The early 'proto-Y' chromosome was originally the same size as the X chromosome and contained all the same genes.
However, Y chromosomes have a fundamental flaw, according to Dr Peter Ellis and Professor Darren Griffin from the University of Kent.
Unlike all other chromosomes, which we have two copies of in each of our cells, Y chromosomes are only ever present as a single copy, passed from fathers to their sons.
This means that genes on the Y chromosome cannot undergo genetic recombination, the 'shuffling' of genes that occurs in each generation which helps to eliminate damaging gene mutations.
Deprived of the benefits of recombination, Y chromosomal genes degenerate over time and are eventually lost from the genome.
Read more: http://www.dailymail.co.uk/sciencetech/article-5787203/The-end-men-Generations-war-blame-collapse-diversity-Y-chromosome.html#ixzz5H18z7rfv
From around 7,000 years ago, something strange seems to have happened to men. Genetic records show that their diversity appeared to have collapsed entirely, and stayed that way for the next 2,000 years. So extreme was the collapse in the Y chromosome that it was as if there were only one man left to mate for every 17 women.
Now scientists think they know why. According to researchers at Stanford University, the collapse was the result of generations of war between clans, whose membership is determined by male ancestors. Pictured is a skeleton from 7,500 BC
Neolithic remains across Europe show tribes likely engaged in violent assaults involving clubs, axes, and arrows about 5,500 years ago.
The 'Neolithic Y-chromosome bottleneck' marks a time when human genetic diversity took a dramatic nosedive.
The slaughter was so severe the male population was decimated to one-twentieth of its original level.
However, by looking at genetic patterns in modern humans, researchers found that the decline was observed only in men - specifically on the Y chromosome, which fathers pass on to their sons.
'An abrupt population bottleneck specific to human males has been inferred across several Old World (Africa, Europe, Asia) populations 5000–7000 BP', researchers, led by Tian Chen Zeng, a Stanford undergraduate in sociology, wrote in their paper published in Nature.
This suggested large numbers of men were dying before having sex and producing children which led researchers to suggest it could a result of generations of warfare.
The team also thought the genetic bottleneck might have been compounded by changing social structures - specifically the creation of patrilineal clans.
After the onset of farming and herding around 12,000 years ago, societies grew increasingly organised around extended kinship groups, which were largely patrilineal.
This cultural fact has potentially significant biological consequences as it is key how clan members are related to each other.
While women may have married into a clan, men in such clans are all related through male ancestors.
This meant they tended to have the same Y chromosomes.
Researchers point out that if there are wars between the clans and wars repeatedly wiped out entire clans over time, they could also wipe out a good many male lineages and their unique Y chromosomes in the process.
This would therefore greatly reduce overall diversity.
The team looked at DNA patterns in modern humans, and their study did not touch on the methods of war that may have driven the Neolithic bottleneck.
http://i.dailymail.co.uk/i/pix/2018/01/23/15/48803F0D00000578-5302565-image-a-6_1516719977902.jpg
The Y chromosome is one of the sex chromosomes in animals and is responsible for the sex determination of unborn offspring. Previous research has suggested the Y chromosome has just 4.6 million years before it completely disappears
This may sound like a long time, but it isn't when you consider that life has existed on Earth for 3.5 billion years.
The early 'proto-Y' chromosome was originally the same size as the X chromosome and contained all the same genes.
However, Y chromosomes have a fundamental flaw, according to Dr Peter Ellis and Professor Darren Griffin from the University of Kent.
Unlike all other chromosomes, which we have two copies of in each of our cells, Y chromosomes are only ever present as a single copy, passed from fathers to their sons.
This means that genes on the Y chromosome cannot undergo genetic recombination, the 'shuffling' of genes that occurs in each generation which helps to eliminate damaging gene mutations.
Deprived of the benefits of recombination, Y chromosomal genes degenerate over time and are eventually lost from the genome.
Read more: http://www.dailymail.co.uk/sciencetech/article-5787203/The-end-men-Generations-war-blame-collapse-diversity-Y-chromosome.html#ixzz5H18z7rfv