You can hold on to your butts thanks to DNA that evolved in fish

There were some indications that the same thing is true in fish, where the elimination of equivalent hox genes also interfered with the formation of the rays at the ends of fins. This would suggest that digits formed by elaborating on a genetic system that already existed in order to produce fins.

However, when a US-French team started looking at the regulation of one set of hox genes in the limbs, things turned out to be a bit more complicated. The hox gene clusters have two…