 These chemicals block the conversion of testosterone to estradiol during development so each sex offspring can be produced at all temperatures.They found that hatching temperatures that naturally produce each sex maximized fitness of each sex, which provides the substantial empirical evidence in support of the Charnov & Bull model for reptiles.Spencer and Janzen (2014) found further support for the Charnov-Bull model by incubating painted turtles ("Chrysemys picta") at different temperatures and measuring various characteristics indicative of fitness.