A tiny genetic alteration may have let vertebrates leave the sea

ABOUT 370m years ago, in the latter part of the Devonian period, the ancestor of all land vertebrates stepped out of the ocean and began to take advantage of the untapped riches found ashore. This was a big step, both literally and metaphorically, and evolutionary biologists have long assumed that bringing about the anatomical shift from functional fin to proto-leg which enabled it to happen required a fortuitous coincidence of several genetic mutations. This, though, may not be the case. A paper just published in , by Brent Hawkins, Katrin Henke and Matthew Harris of Harvard University, suggests the process was propelled by a single genetic change of the smallest sort possible.The better to understand the origin of tetrapods, as land vertebrates are known collectively to zoologists, the trio were looking at what happened to zebrafish (a common subject of experiments in developmental biology because they are small, transparent and breed prolifically) when they made minor tweaks to those fishes’ genes. Searching through more than 10,000 mutated specimens they noticed that one group of mutants sported an unusual pattern of bones in their pectoral fins. Instead of having four, they had six.