Even though researchers in other areas widely appreciated the breakthroughs in Drosophila development, they questioned the relevance of the information to vertebrate development. Vertebrates, as chordates, were thought to have branched from arthropods long ago and last shared a very simple common ancestor in the pre-Cambrian era (about 540 million years ago). The two groups were thought to have evolved their segmentation and heads independently. One of the first significant similarities between vertebrate and fly development came from work on homeotic genes, now called Hox genes. As mentioned before, the Hox genes are expressed in eight broad bands or spatial compartments in the anteroposterior dimension of the body shortly after gastrulation but prior to organogenesis and cytodifferentiation. Their encoded products make each spatial compartment different from the others.
The study of the eight Hox genes of Drosophila was primarily pioneered by E. Lewis from 1940 to 1970. For his work in that area, he shared the Nobel Prize