Off the coast of American Samoa, the tropical sun beats down on a shallow tidal lagoon, heating the water to a sizzling 35 °C for a few hours each day. Such temperatures would kill off most coral reefs, and yet the Samoan lagoon hosts courtyards of antler-like branching corals and mound corals the size of refrigerators. “The fact that they're there means they've adapted to survive,” says Steve Palumbi, a marine biologist at Stanford University in California. “The real question is: how did they do that and can all corals do that?”Palumbi is just starting to understand how these Samoan corals thrive in such extreme conditions. And he thinks he might be able to harness that ability to create a reef of hardy coral with a chance of surviving the hot seas that are expected to result from climate change. Starting in August, he and his team are going to try to plant “the smartest future reef we can imagine”.Palumbi is part of a small group of coral researchers around the world tackling such issues to throw threatened reefs a lifeline. Their ultimate intent is to launch a programme of 'human-assisted evolution', creating resistant corals in controlled nurseries and planting them in areas that have been — or will be — hard-hit by changing conditions. “It's a brave new world of working with corals in this way,” says Ruth Gates, a marine biologist at the University of Hawaii at Manoa who, along with coral geneticist Madeleine van Oppen at the Australian Institute of Marine Science in Townsville, is helping to pioneer the field.The work is not without controversy. Although no one is yet attempting to create genetically modified corals, some researchers are concerned that human-assisted evolution goes too far down the slippery slope of altering natural systems. “If you're basically farming a reef, you've taken a natural habitat and you've converted it,” says Steve Vollmer, a coral geneticist at Northeastern University's Marine Science Center in Nahant, Massachusetts, who feels that more needs to be known before embarking on such programmes. “It's like going to the Midwest and taking grasslands and making it into soy. There are huge implications to doing this.”