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DNA mutations may happen slower than thought; species split may have happened further back
Putting our DNA clocks back
One of the most important tools in evolutionary biology over the last thirty or so years has been the development of the ‘molecular clock’, which is a technique for measuring how long ago two organisms (or taxa or species) separated on the ‘tree of life’. This approach has been incredibly powerful, and underlies much of our understanding of the rate of evolution, linking fossil and molecular data – all the figures from the excellent Timetree.org are based on the molecular clock. But now it appears that in our lineage at least, the clock may not have been ticking quite so fast as we thought, and some recalibration is going to be necessary.
...
A review by Aylwun Scally and Richard Durbin, recently published in Nature Reviews Genetics, reveals that over the last decade, nine studies have come out with substantially lower mutation rates, suggesting our clocks have been running far too fast. These studies have looked at mutation rates across the whole genome, and have focused on particular genes, including one study of over 14,000 people. They all suggest that the actual mutation rate is about half that previously estimated. To put this into perspective, a study of 78 families from Iceland (mother, father, child) found that on average, a baby has 36 spontaneous mutations that are not present in either parent. Depending on where you grew up – presence of natural radiation etc – the number of spontaneous mutations in your genes is probably not too far different.
So what happens when this new, lower, figure is plugged into our estimates of divergence times for the various twigs and branches on the tangled bank of recent human evolution? Because the clock is now thought to be ticking more slowly than we originally estimated, the divergence times are being put back. So, for example, the human/Neanderthal split was estimated at between 272,000-435,000 years ago. The new figure would appear to be something more like 400,000-600,000 years.
This removes an odd discrepancy, as previous estimates of human/Neanderthal divergence using mitochondrial DNA (mtDNA is found in the tiny mitochondria of our cells, which are inherited maternally, and which are involved only in the generation of energy) had come up with a figure 0f 500,000-600,000 years ago. So both nuclear DNA and mtDNA now give a similar estimate – we split from our Neanderthal cousins about half a million years ago. Not that that stopped us mating with them and getting some of their genes… In terms of the time when we left Africa (based on genetic differences between non-African and African populations), that figure used to be put at around 70,000 years ago; it now appears to have been substantially earlier, perhaps 90,000-130,000 years ago.
http://whyevolutionistrue.wordpress.com/2012/10/14/putting-our-dna-clocks-back/
One of the most important tools in evolutionary biology over the last thirty or so years has been the development of the ‘molecular clock’, which is a technique for measuring how long ago two organisms (or taxa or species) separated on the ‘tree of life’. This approach has been incredibly powerful, and underlies much of our understanding of the rate of evolution, linking fossil and molecular data – all the figures from the excellent Timetree.org are based on the molecular clock. But now it appears that in our lineage at least, the clock may not have been ticking quite so fast as we thought, and some recalibration is going to be necessary.
...
A review by Aylwun Scally and Richard Durbin, recently published in Nature Reviews Genetics, reveals that over the last decade, nine studies have come out with substantially lower mutation rates, suggesting our clocks have been running far too fast. These studies have looked at mutation rates across the whole genome, and have focused on particular genes, including one study of over 14,000 people. They all suggest that the actual mutation rate is about half that previously estimated. To put this into perspective, a study of 78 families from Iceland (mother, father, child) found that on average, a baby has 36 spontaneous mutations that are not present in either parent. Depending on where you grew up – presence of natural radiation etc – the number of spontaneous mutations in your genes is probably not too far different.
So what happens when this new, lower, figure is plugged into our estimates of divergence times for the various twigs and branches on the tangled bank of recent human evolution? Because the clock is now thought to be ticking more slowly than we originally estimated, the divergence times are being put back. So, for example, the human/Neanderthal split was estimated at between 272,000-435,000 years ago. The new figure would appear to be something more like 400,000-600,000 years.
This removes an odd discrepancy, as previous estimates of human/Neanderthal divergence using mitochondrial DNA (mtDNA is found in the tiny mitochondria of our cells, which are inherited maternally, and which are involved only in the generation of energy) had come up with a figure 0f 500,000-600,000 years ago. So both nuclear DNA and mtDNA now give a similar estimate – we split from our Neanderthal cousins about half a million years ago. Not that that stopped us mating with them and getting some of their genes… In terms of the time when we left Africa (based on genetic differences between non-African and African populations), that figure used to be put at around 70,000 years ago; it now appears to have been substantially earlier, perhaps 90,000-130,000 years ago.
http://whyevolutionistrue.wordpress.com/2012/10/14/putting-our-dna-clocks-back/
