I get a lot of emails. Most can be casually filed away, but among the spam and fluff from PR agencies, there are occasionally some absolute gems. And so it was that on August 21st, one Paul Sanders saw fit to send me four photos of a chicken.

Several months back, I wrote a piece about chickens that caught Paul’s eye. In a new paper, Mike Clinton’s group at the University of Edinburgh had found that these everyday birds have an amazing secret – every single cell in their bodies is either male or female. Each one has its own sexual identity, which is very different from the way that sex is determined in mammals.

Sanders grew up on