Correction Appended

By reconstructing ancient genes from long-extinct animals, scientists have for the first time demonstrated the step-by-step progression of how evolution created a new piece of molecular machinery by reusing and modifying existing parts.

The researchers say the findings, published today in the journal Science, offer a counterargument to doubters of evolution who question how a progression of small changes could produce the intricate mechanisms found in living cells.

"The evolution of complexity is a longstanding issue in evolutionary biology," said Joseph W. Thornton, professor of biology at the University of Oregon and lead author of the paper. "We wanted to understand how this system evolved at the molecular level. There's no scientific controversy over whether this system evolved. The question for scientists is how it evolved, and that's what our study showed."

Charles Darwin wrote in The Origin of Species, "If it would be demonstrated that any complex organ existed which could not possibly have formed by numerous, successive, slight modifications, my theory would absolutely break down."