"Fisheries are known to exert selective pressure on fish. In some cases this has led to the evolution of smaller fish. This was thought to be a slow process. “Previous workers have concluded that evolutionary changes are only observable on a longer timescale, of decades,” Árnason says. “The changes we observe are much more rapid.” The A gene is being driven out simply because of where those fish choose to live, says Árnason. Such inadvertent, rapid selective pressure may drive some fisheries to crash. “Man the hunter has become a mechanised techno-beast,” the team writes. “Modern fisheries are uncontrolled experiments in evolution.” Worryingly, the researchers found that cod in the Icelandic fishery are becoming sexually mature while still smaller and younger. Something similar occurred in Newfoundland cod just before that fishery crashed. “We think this too is an evolutionary response to the selective pressure of fisheries,” says Árnason." - Steven Perez from Bookmarklet