What distinguishes humans from monkeys, besides a large brain and upright walking? In a new study, scientists found that humans have far fewer DNA mutations than their closest living relatives. It turns out that our evolution is about a third slower. The scientific publication "Wiedenskub" tells about new discoveries made thanks to this research.
What makes humans different from monkeys?
You may have asked this question before. Big brain? Walking upright? Thumbs up?
Maybe. But it looks like there is more. In a new study, Danish scientists have found that humans have far fewer DNA mutations than our closest living relatives, the great apes.
That is, our genes are not so different from our parental ones, as is the case in great apes.
“A human baby is born with fewer mutations than a baby chimpanzee. Our evolution is about a third slower than that of other primates,”Mikkel Heide Schierup, professor at the Center for Bioinformatics at Aarhus University and co-author of the new study, told Wiedenskub.
Together with geneticist Christina Hvilsom of Copenhagen Zoo and Aarhus University bioinformatist Søren Besenbacher, he compared the frequency of human mutations to that of chimpanzees, gorillas and orangutans.
The results indicate that the human mutation rate has dropped dramatically over the past millions of years. The study was recently published in the scientific journal Nature Ecology and Evolution.
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More and more mutations occur over time
Mutations happen when our cells divide. For example, try to take a close look at your hands.
Maybe there are more wrinkles there than before? It should be. Daily activities and ultraviolet radiation from the sun are constantly destroying our cells. Fortunately, cells regenerate on their own.
“In 99.9% of cases, they are restored without errors. But over time, more and more errors, also called mutations, will appear during recovery,”says Mikkel Heide Schirup.
Mutations show how we evolved
In the case of mutations that occur in the fetus in the uterus, we are talking about changes that occur during cell division and are not inherited from the mother or father.
In this case, however, it is wrong to call them all errors, says Mikkel Heide Schirup. Mutations can be beneficial, harmful, or irrelevant.
“Many mutations do not appear in any way, and it is they that we use to determine the time of origin of the species. Most of the harmful mutations quickly disappear, and a small number of beneficial ones spread and give the species new properties,”says Mikkel Heide Schirup.
Mutations can tell when a person appeared
According to Mikkel Heide Schirup, different mutation rates can be used to determine when the ancestors of humans and great apes split and became different species.
If you look at the frequency of human mutations, it turns out that you have to go back about 10 million years to get to the time when we parted with chimpanzees.
“But when you consider that the mutation rate in chimpanzees is higher than ours, it turns out that humans diverged from chimpanzees about 6.6 million years ago, and this is much better consistent with the fossil finds that we have,” says Mikkel Heide Schirup.
Scientists can figure this out by looking for mutations in the chimpanzee's genome and comparing them to the number of mutations they pass on over a generation. Chimpanzee mutation rates are consistent with fossil findings.
For example, in the period from 2001 to 2002 in the Chad Desert in Africa, several fossils were found of the early Sahelanthropus tchadensis great ape, considered the common ancestor of humans and chimpanzees. Sahelanthropus lived seven million years ago.
Scientist: a very interesting study
Evolutionary biologist Morten Allentoft of the National Museum of Natural History read this study. And he's inspired.
“This is a serious study with a very interesting approach. They calculated the common genome of several families of monkeys, which provided an impressive amount of data,”he told Wiedenskub.
“For some time there was confusion about the strange discrepancy between the mutation frequency in the human genome and the age of the fossils when it came to our evolutionary division with great apes. Instead of studying humans, the researchers here turned the problem around and studied our closest relatives. And now they are finding data that is just consistent with the fossil finds."
"Therefore, we humans are the strangest monkey in this context."
Researchers: something could have happened during the exodus from Africa
According to Mikkel Heide Schirup, it is difficult to understand when a person's mutation frequency began to drop. But he suggests that this happened relatively recently. Perhaps only 200-300 thousand years ago.
Morten Allentoft agrees with Mikkel Heide Schirup that it appears that mutation rates in humans have declined relatively recently. And by "recently" is meant a range within the last million years.
“It probably happened on the last stretch of the branch. If this happened earlier, then the picture would not be consistent with the age of the fossils, because we would have to separate earlier than the period that some of the finds are dated, but we believe that these are our common ancestors,”he says.
It is unknown why we have fewer mutations
however, it is difficult to say what could be the cause of the decrease in mutation rates. Perhaps this is a change in the environment and living conditions, Morten Allentoft suggests.
“We left Africa and took over the entire globe. We were influenced by all sorts of environmental factors that might not affect other great apes. Nobody knows how all this could affect the rate of mutations."
“Lots of things can make a difference,” says Mikkel Heide Schirup. "Both environmental and biological factors, such as the fact that we later grow up and have children."
Human mutation frequency is studied mainly in Europeans
The next step in the study, among other things, will be to examine the mutation rates among more monkeys to provide a more accurate estimate. Also, the researchers are going to include in their work another large apes - the bonobos.
In addition, the researchers must test the mutation rates in more different people, says Mikkel Heide Schirup.
“Unfortunately, we collected information on the frequency of mutations mainly on the material of the European population, so now we need to find out if the picture could be different in other parts of the world,” says Mikkel Heide Schirup.
Morten Allentoft agrees that this should be the next step.
“It will be interesting to see if the mutation rates are different, for example, among the indigenous people of the Amazon or Africa. Perhaps this will give us information about where and when in our evolutionary history this indicator decreased and whether it happened after the exodus from Africa."
Found more mutations than expected
The new study looked at a total of ten monkey families of mother, father, and cubs: seven chimpanzee families, two gorilla families and one orangutan family.
The researchers documented a number of new mutations, finding genetic variants that were only present in the child and not in the parents.
This was done by a genome sequencing technique used to determine the DNA of an organism.
In all families, the researchers found more mutations in the young than expected based on the data on mutations in humans.
Scientists also drew on materials from previous studies that examined the frequency of mutations in humans.
Asbjørn Mølgaard Sørensen