Last year more than 81,000 people were adopted in Japan, one of the highest rates in the world. But, amazingly, over 90% of those adopted were adults. The practice of adopting men in their 20s and 30s is used to rescue biologically ill-fated families and ensure a business heir, says Vikas Mehrotra, of the University of Alberta, the paper’s lead author. “We haven’t come across this custom in any other part of the world.”