Long before our ancient fish ancestors had even vaguely considered that the dry land might be a place to colonize, they had the genetic switches ready to make limbs and digits — switches which still function on mammals today.


This research was prompted by the discovery of Tiktaalik — a walking fish discovered in 2004. Tktaalik had a limb structure remarkably similar to land mammals, prompting scientists to dig into just how far back our limb coding goes.

Researchers at the University of Chicago found that the genetic switch that activates limbs and digits in mammals currently goes back millions of years to ancient fish. How do scientists know these genes were present that long ago? The researchers found the genes that code for limbs in mice, chickens, frogs, zebrafish and skates — all of whom shared an ancestor around 400 million years ago.


The genetic switch is known as CsB, and what they found was that the mouse CsB could activate on the fins of the zebrafish, and that the fish CsB could activate on the limbs and digits of the mice (pictured above). Millions of years before mutant fishes developed limbs, that familiar pentadactyl array was waiting in the genes of early fish, ready to be activated. Who knows what waits in our genes now, getting ready to mutate us into something even weirder than we already are?