In the 1980s, researchers discovered a series of genes called Hox genes that set the identity of segments of insect bodies from head to tail. Mutations to Hox genes can put an entire leg where an antenna should sprout out (right) and produce other equally grotesque transformations.
Interestingly, insects and humans also inherited Hox genes. In us, these genes control the development of our head-to-tail anatomy as embryos. Similar genes controlling the eyes of insects and our own eyes have also been discovered. (Our version of the gene can be inserted in a fly and still trigger the building of an insect eye!) It now appears that some 600 million years ago, a common ancestor of most animals on Earth today acquired a “genetic toolkit” of these body-building genes. Although the structures that these genes build have changed, the genes have been conserved. It is a discovery that would have delighted Darwin — and astonished him greatly.