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 track the emergence of a novel physical trait, the first step toward the creation of a new species. For the first time, researchers had direct access to the machinery of evolution and could actually watch it in the act. A new science, known as evolutionary developmental biology, or evo devo, was born.
One of the great triumphs of modern evolutionary science, evo devo addresses many of the key questions that were unanswerable when Charles Darwin published On the Origin of Species in 1859, and Carroll has become a leader in this nascent field. Now a professor of molecular biology and genetics at the University of Wisconsin, he continues to decode the genes that control life’s physical forms and to explore how mutations in those genes drive evolutionary change. These days, Carroll also devotes increasing energy to telling the public about his field’s remarkable discoveries through a series of books—Endless Forms Most Beautiful, The Making of the Fittest, and the brand-new Remarkable Creatures. He spoke with DISCOVER senior editor Pamela Weintraub about what his work has taught him about Darwin, the nature of evolution, and how life really works.
It has been 150 years since Charles Darwin proposed his theory of evolution in On the Origin of Species, yet in some ways the concept of evolution seems more controversial than ever today. Why do you think that is? It is a cultural issue, not a scientific one. On the science side our confidence grows yearly because we see independent lines of evidence converge. What we’ve learned from the fossil record is confirmed by the DNA record and confirmed again by embryology. But people have been raised to disbelieve evolution and to hold other ideas more precious than this knowledge. At the same time, we routinely rely on DNA to convict and exonerate criminals. We rely on DNA science for things like paternity. We rely on DNA science in the clinic to weigh our disease risks or maybe even to look at prognoses for things like cancer. DNA science surrounds us, but in this one realm we seem unwilling to accept its facts. Juries are willing to put people to death based upon the variations in DNA, but they’re not willing to understand the mechanism that creates that variation and shapes what makes humans different from other things. It’s a blindness. I think this is a phase that we’ll eventually get through. Other countries have come to peace with DNA. I don’t know how many decades or centuries it’s going to take us.
