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