We don’t wish to alarm you, but your mutations just aren’t what they were a million years ago. Sorry.
By comparing genetic changes in the offspring of various primates, researchers have determined the mutation rate of humans has slowed since we parted ways. X-Men franchise fans might be disappointed, but the results could clear up some questions about our past.
We’ve been fascinated with our own genetic material for as long as we’ve been able to study it, and have done a pretty thorough job of not only mapping our genes, but working out the rates at which they change.
“Over the past six years, several large studies have done this for humans, so we have extensive knowledge about the number of new mutations that occur in humans every year,” says population geneticist Søren Besenbacher from Aarhus University.
“Until now, however, there have not been any good estimates of mutation rates in our closest primate relatives.”
Researchers from Aarhus University and Copenhagen Zoo collected genetic information from the parents and offspring of chimpanzees, gorillas, and orangutans to compare their mutation rates with our own.
An analysis of their DNA sequences revealed the number of new mutations that appeared in each generation, allowing the team to compare figures across diverse branches of the primate family tree.
Compared with similar data collected on humans, and accounting for relative differences in the ages of the parents, the mutation rate in each of the ten ape families studied averaged out at around 150 percent greater than our own.
The results also suggest this slowdown started relatively recently in our history, perhaps as little as 400,000 years ago, not long before our ancestors qualified as modern humans.
This change has some pretty significant consequences when it comes to using our genes as a tape measure for mapping our evolutionary past.
Like the ticking of a metronome, we can use the ‘beats per minute’ of mutating DNA to figure out when two related species were last members of the same band.
If we go by the modern human beat, the last ancestor we had in common with our closest cousin, the chimpanzee, existed around 10 million years ago. Indeed, one study pinpoints our split at around 13 million years in the past.
Other genetic measures, though, could suggest a split closer to 4 million years. Just to add to the confusion, the fossil record disagrees with both estimates, suggesting a split closer to 8 million years ago.
The new results could help clarify this discrepancy, leaning towards a separation of around 6 to 7 million years.
“The times of speciation we can now calculate on the basis of the new rate fit in much better with the speciation times we would expect from the dated fossils of human ancestors that we know of,” says senior researcher Mikkel Heide Schierup from Aarhus University.
It could also prompt us to rethink the divergence of Neanderthal and modern human ancestors, requiring us to recalculate estimates based on a slightly higher mutation rate than we currently do.
Just what might have caused this slowdown is anybody’s guess. The researchers speculate it could have something to do with our late-onset puberty and longer generation spans. Or changes in environment and lifestyle.
It’s unlikely to have affected the rate at which our genes spread and help us adapt – our evolution has been barrelling along at break neck speeds.
Knowing more about the relationship between genetic change and adaptation could do more than help us understand our own history. It could spell out the future for the entire branch of our family tree.
“All species of great apes are endangered in the wild,” says Copenhagen Zoo’s Christina Hvilsom.
“With more accurate dating of how populations have changed in relation to climate over time, we can get a picture of how species could cope with future climate change.”
This research was published in Nature Ecology & Evolution.