How turning down the heat makes a baby turtle male. Duke Today, May 10, 2018. Scientists have started to crack the 50-year-old puzzle of how temperature turns baby turtles male or female. In a study in the journal Science, researchers show that cooler egg incubation temperatures turn up a key gene called Kdm6b in the turtle’s immature sex organs. This in turn acts as a biological “on” switch, activating other genes that allow testes to develop without altering the underlying genetic code. Picked up by Science News and BBC News.