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http://www.sciam.com/article.cfm?id=regulating-evolution

Switches within DNA that govern when and where genes are turned on enable genomes to generate the great diversity of animal forms from very similar sets of genes

KEY CONCEPTS

- Because genes encode instructions for building animal bodies, biologists once expected to find significant genetic differences among animals, reflecing their great diversity of forms. Instead very dissimilar animals have turned out to have very similar genes.

- Mutations in DNA "switches" that control body-shaping genes, rather than in the genes themselves, have been a significant source of evolving differences among animals.

- If humans want to understand what distinguishes animals, including ourselves, from one another, we have to look beyond genes.

At first glance, the list of animals could suggest any zoo. There's an elephant, an armadillo, an opossum, a dolphin, a sloth, a hedgehog, big and small bats, a couple of shrews, some fish, a macaque, an orangutan, a chimpanzee and a gorilla—to name a few of the more familiar creatures. But this menagerie is not at all like any zoo that has been constructed before. There are no cages, no concession stands and, in fact, no animals. It is a "virtual" zoo that contains only the DNA sequences of those animals—the hundreds of millions to billions of letters of DNA code that make up the genetic recipe for each species.

The most excited visitors to this new molecular zoo are evolutionary biologists, because within it lies a massive and detailed record of evolution. For many decades, scientists have longed to understand how the great diversity of species has arisen. We have known for half a century that changes in physical traits, from body color to brain size, stem from changes in DNA. Determining precisely what changes to the vast expanse of DNA sequences are responsible for giving animals their unique appearance was out of reach until recently, however.

Biologists are now deciphering the DNA record to locate the instructions that make assorted species of flies, fish or finches look different from one another and that make us humans different from chimpanzees. This quest has led to a profound change in our perspective. For most of the past 40 years or so, researchers have focused most of their attention on genes—the nucleotide sequences in DNA that encode the amino acid chains that form proteins. But to our surprise, it has turned out that differences in appearance are deceiving: very different animals have very similar sets of genes. By following the trail of evolution, devices are being found within DNA—genetic "switches"—that do not encode any proteins but that regulate when and where genes are used. Changes in these switches are crucial to the evolution of anatomy and provide new insights into how the seemingly endless forms of the animal kingdom have evolved.

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