Quoted: Biologist Sean B. Carroll of the University of Wisconsin-Madison, author of The Making of the Fittest (W.W. Norton & Co.) and other popular books on evolution, says evolutionary leftovers are born of a “use it or lose it” system.
For example, he says, we carry damaged versions of genes for dozens of smell receptors that give mice and other mammals far sharper noses. “Our repertoire of smell-receptor genes has gone to pot,” Carroll says.