Essential genes are often thought to be frozen in evolutionary time — evolving only very slowly if at all, because changing or dying would lead to the death of the organism. 100s of millions of years of evolution separate insects and mammals, but experiments show that the Hox genes guiding the development of the body plans in Drosophila fruit flies and mice can be swapped without a hitch because they are so similar. This remarkable evolutionary conservation is a foundational concept in genome research.

But a new study turns this rationale for genetic conservation on its head. Researchers at the Fred Hutchinson Cancer Research Center in Seattle reported last week in eLife that a large class of genes in fruit flies are both essential for survival and evolving extremely rapidly. In fact, the scientists’ analysis suggests that the genes’ ability to keep changing is the key to their essential nature. “Not only is this questioning the dogma, it is blowing the dogma out of the water

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