Is it a boy or is it a girl? For baby sea turtles it’s not that cut and dry. Because they don’t have an X or Y chromosome, baby sea turtles’ sex is defined during development by the incubation environment. The nest’s thermal environment determines whether an embryo will develop as a male or female. Warmer sand temperatures produce more females and cooler sand temperatures produce more males. To make things even more complicated, in some species of sea turtles, their sexual anatomy is not physically apparent until about a decade or so when they approach sexual maturity.