A new international study published this week in Nature challenges long-held beliefs about the evolutionary origins of fingers. Researchers at the University of Geneva and the Collège de France have identified a surprising link between finger growth and the formation of the cloaca in fish, offering a novel viewpoint on the transition of life from water to land. The work, utilizing both zebrafish and mice, reveals that the same genetic programming responsible for cloaca development is repurposed to form our digits – a counterintuitive discovery with implications for understanding vertebrate evolution.
Where do our fingers come from? How did they emerge during evolution? Researchers at the University of Geneva and the Collège de France have now answered this long-standing question in biology in a surprising way. (Originally published October 12, 2025)
The origin of fingers has puzzled the scientific community for over a century, largely because it’s intrinsically linked to one of the most fascinating mysteries in the history of life: the transition from water to land around 380 million years ago. How did our fish ancestors evolve into the diverse array of vertebrate species we see today, equipped with both lungs for breathing air and limbs ending in fingers for terrestrial movement? How did evolution transform fish fins into articulated extremities capable of grasping?
The prevailing theory suggested that fingers are simply anatomical extensions of fish fin rays. An alternative hypothesis proposed that fingers were entirely new structures, “invented” by life as it adapted to life on land. However, a new international study, published September 17 in Nature, challenges both of these ideas.
Fingers, and the extremities they comprise, have a surprising and previously unknown origin – a repurposed ancient genetic program involved in the formation of the cloaca. This is the common posterior opening for the digestive, urinary, and reproductive systems in fish.
A Counterintuitive Discovery
By comparing embryos of zebrafish and mice, researchers discovered that the Hox genes – often referred to as the architect genes or master regulators of limb formation in mice – are the same genes that orchestrate cloaca development in fish. Using CRISPR gene-editing technology, they confirmed that mice lacking these regulatory genes developed finger malformations, while zebrafish exhibited cloaca abnormalities. This finding underscores the power of genetic tools in unraveling evolutionary mysteries.
“The commonality between the cloaca and the fingers,” explained Aurélie Hintermann, a co-author of the study, in a University of Geneva press release, is that they both represent terminal parts. Whether it’s the end of the digestive tube or the end of the feet and hands – that is, the fingers – both mark the end of something.”
Professor Denis Duboule, from the Collège de France and a leading researcher on the study, added: “The fact that the same genes are involved is a striking example of how evolution innovates by recycling the old to create the new. Rather than building a new regulatory system for fingers, nature repurposed an existing mechanism initially active in the cloaca.”
The findings offer a new perspective on the strategies employed by life: reuse and recycle rather than reinvent. It also serves as a humbling reminder that the very structures we rely on – our fingers – share a common developmental origin with the cloaca of fish.
