“The implications of introducing a second intelligent species onto Earth are far-reaching enough to deserve hard thinking.”1 So ended The Economist magazine’s review of Nick Bostrom’s Superintelligence. Most would interpret this as a classic example of British understatement. Surely, you might think, the great minds of today are already doing this hard thinking—engaging in serious debate, weighing up the risks and benefits, seeking solutions, ferreting out loopholes in solutions, and so on. Not yet, as far as I am aware.”