About 54 million years ago, a semiaquatic deerlike creature headed into the water for good, giving rise to whales and their relatives. The newly sequenced genome of the minke whale, a baleen whale found worldwide, tells the story of how stressful this move to live underwater was. An international team has decoded the genomes of four minke whales, a fin whale, a bottlenose dolphin, and a finless porpoise, comparing these cetaceans’ genes to the equivalent genes in other mammals. It found whale-specific mutations in genes important for the regulation of salt and of blood pressure and for antioxidants that get rid of charged oxygen molecules that can harm cells. These molecules increase in number as the whale uses up its oxygen supply during dives. Whales also had larger numbers of related genes, called gene families, for dealing with sustained dives, the team reports online today in Nature Genetics. Overall, 1156 gene families had expanded, and several increased the number of enzymes that help the whale cope with low-to-no oxygen conditions. A few of those expanded families are also expanded in naked mole rats, which live underground where oxygen is scarce. But the numbers of genes for body hair and for taste and smell had decreased. And of course, there were genes and gene families that help explain why whales look the way they do.