When Sean Carroll was a graduate student at Tufts School of Medicine in Boston, he found himself seduced by spectacular new studies of the humble fruit fly. That work, which eventually won a Nobel Prize for its principals, showed that modifying a single gene during a fly’s embryonic development could transform the insect’s body plan: Instead of becoming an antenna, a body extension could develop into a leg. Carroll continued to study these genes and, some years later, found that they were not restricted to fruit flies; they turned out to be part of a master tool kit that sculpts the body structures of all animals, ranging from humans to nematode worms.
The discovery of this small set of universal body-building genes gave Carroll and others a fresh way to explore the inner workings of evolution. By observing how the genes changed during the course of embryonic development, scientists could ...
