25 November 2022

Evolution and genes

Geneticists have identified the key DNA sites for the development of our species

Sergey Vasiliev, Naked Science

In comparison with their closest relatives, chimpanzees and other representatives of the hominid family, humans are distinguished by a particularly large brain and a short intestine. These traits are considered not only extremely important for our species, but also mutually opposite: both the brain and the intestine consume huge amounts of resources, and the body cannot afford to develop both.

It seems that the choice in favor of the brain was made shortly after seven million years ago, after the separation of the line of our direct ancestors from other great apes, but before diverging from the line of Neanderthals. Such conclusions were reached by geneticists from the American Duke University, whose article was published in the latest issue of the journal Cell (Mangan et al., Adaptive sequence divergence forged new neurodevelopmental enhancers in humans).

As a rule, the search for genetic features specific to our species is focused on genes — DNA sections that encode proteins. However, the DNA of humans and their closest relatives, chimpanzees, differ too little, and the genes are almost identical. The main difference is due to non-coding DNA regions that can perform other important functions, primarily regulatory ones, controlling the work of chromatin and the genes themselves.

It was on such sites that the geneticists from the Craig Lowe team concentrated. They found a number of fragments that changed rapidly after the divergence of our ancient ancestors from chimpanzees about 7.4 million years ago. Scientists called them HAQERS (Human Ancestor Rapidly Evolved Regions — "rapidly developed regions of the human ancestor") and showed that they are involved in the development of the body, primarily the brain and intestines. Being located close to the corresponding genes, they regulate their work in the right place and at the right time.


Fluorescent tags demonstrate the activity of genes in the cortex of the developing mouse brain. On the left — with the "ancient" HAQER0059, on the right — with the modern, human / © Riley Mangan, Duke University

"We see that not one mutation has given us a big brain and not one has changed the intestines: it was a lot of changes that took place for a while," explains Professor Low. "We see a lot of regulatory elements that act in these tissues, determining which genes will be expressed and with what activity."

The role of HAQERS was also confirmed in experiments. To do this, scientists used laboratory mice that had one of these fragments, HAQER0059, inserted into the cerebral cortex at the intrauterine stage of development. One group of animals received HAQER0059 of modern humans, the other — a reconstructed version that was present in DNA more than six million years ago. Indeed, the modern HAQER0059 dramatically enhanced the work of the genes responsible for the development of a powerful cortex.

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