Humanity’s ability to alter nature, a characteristic of our species for thousands of years, has taken a big step forward. The ability to change the genetics of life to our liking was previously confined to domesticated creatures such as livestock and crops. It now extends throughout much of the biosphere, including ourselves. Genetic engineering on a planetary scale used to be the stuff of science-fiction dreams, and sometimes nightmares. But now the potential has arrived. For the first time, discussions about quickly transforming entire ecosystems are no longer hypothetical.