What decides the sex of a Greek tortoise?

   On a bright May morning, the undergrowth rustles as a male Greek tortoise searches for a mate. With the air temperature around 27 °C (80 °F), his body has been warmed into activity and he hurries at about ¼ mph (0.4 km/h) up to a tortoise feeding on leaves and grass close by. He butts his domed, Sin (200mm) shell against the other's and takes a nip at its legs. A female ready for mating will stand still for him, but an unwilling female - or another male - will simply walk away. Mating is a difficult business for a tortoise, because the female's shell is slippery and very rounded. Success is generally marked by high-pitched calls from the male.
   The female lays about 12 hard-shelled eggs in a nest dug in the dusty soil. The white, oval eggs, about 1 in (25mm) across, take about three months to hatch, but the exact time depends on the soil temperature. A warmer temperature speeds up development, a cooler temperature slows it down, and extremes of temperature can kill the developing embryos altogether.
   The soil temperature governs more than hatching time. It determines sex. Eggs laid and buried in a temperature above 30 °C (86 °F) produce a higher proportion of females. Cooler temperatures favour males. Whatever their sex, the tiny, rounded babies tumble from the nest and scuttle off into the undergrowth, indepen­dent from the moment they hatch until they die — which may be more than 100 years later.