380 million years ago, Our Ancestors the fish began to colonize dry land, evolving into numerous vertebrate species equipped with hands and feet for locomotion. Understanding how these structures evolved remains one of the most hotly debated questions in evolutionary biology ; do fish have fingers ?
By comparing the genomes of mice and fish, an international research team led by Prof. Denis Duboule, holder of the Evolution of Development and Genomes chair at the Collège de France, first noted the presence in fish of a gigantic region of DNA that in mice helps to make fingers. The research team then used CRISPR molecular scissors to remove this piece of DNA from the fish, and surprisingly observed a loss of gene expression in the cloaca, even though the fins were unaffected.
This surprising result suggests that an important genetic system for the cloaca - the orifice where the intestinal, excretory and reproductive systems meet at their extremities in many species - has been reused in terrestrial vertebrates to develop fingers. " What the cloaca and fingers have in common is that they represent terminal parts, either the end of tubes in the digestive system, or the end of arms and legs. So they both mark the end of something ", says Aurélie Hintermann, first author of this publication (17 September 2025) in Nature magazine .
This study illustrates how evolution innovates, recycling the old to make the new. Rather than producing a new regulatory system for fingers, nature has hijacked an existing device, initially active in the cloaca.
