Scientists stunned by the solution to the mystery of the origin of fingers in humans

An international group of researchers has proposed an unexpected explanation for the origin of fingers in terrestrial animals. Their appearance is not directly related to fish fins, but to the "repurposing" of an ancient genome region that originally controlled the development of the cloaca - an organ where digestive, excretory and reproductive systems converge. The work is published in the journal Nature.

About 380 million years ago, ancestors of modern fish began to adapt to land. One of the main questions in evolutionary biology remains how limbs with fingers appeared: are they a modification of fins or a fundamentally new structure?

To answer this, scientists studied not only the genes themselves, but also extensive non-coding DNA regions - so-called regulatory landscapes that control the activation and deactivation of genes. Comparing mouse and fish genomes, researchers found a common region associated with finger development in mammals. When this region was removed in fish using CRISPR/Cas9 technology, the genes stopped working not in the fins, but in the cloaca.

"What's common between the cloaca and fingers is that they are always at the ends - whether it's the end of the digestive system tube or the end of a limb. Evolution simply used an already existing mechanism in a new context," explained study co-author, biologist Aurelie Hintermann.

This involves regulatory landscapes that control the activity of Hox genes - the so-called "architects" of the organism that set the body's structural plan.

"This is a striking example of how evolution works: the new is born from the old," noted Professor Denis Duboule. "Instead of creating a new regulatory mechanism for fingers, nature repurposed one that already existed."

Thus, it was not so much the coding genes themselves, but the architecture of their regulation that became the driver of evolutionary changes. According to the authors, understanding such "repurposing" will help to better explain how modern terrestrial animals, including humans, evolved from fish.