In some species, low temperatures produce mainly females, and high temperatures produce mostly males. Apparently, in animals where both occur, certain incubation temperatures can "reverse" the genotypic sex of an embryo.
Sunderland MA : Sinauer Associates; Bibcode : Sci
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We also examined the gonadal expression of the three primary, catalytically active DNA methyltransferase enzymes and show that they are present during critical stages of gonadal development. An alternative hypothesis of adaptive significance was proposed by Bulmer and Bull in  and supported by the work of Pen et al.
Sunderland MA : Sinauer Associates; Annual Review of Genetics. ScienceDaily, 31 July Temperature-dependent sex determination in three reptile species: the American alligator Alligator mississippiensisthe red-eared slider turtle Trachemys scripta elegansand the alligator snapping turtle Macroclemys temminckii.
Over the next two decades, scientists worked to test mechanisms of sex differentiation in more species and to pinpoint pivotal temperatures, which are species-specific temperature ranges in which males and females are produced in equal number.
The warming of the habitats of species exhibiting TSD are beginning to affect their behavior and may soon start affecting their physiology. While aromatase activity remains low for much of development in individuals that exhibit TSD, during the thermosensitive period, variations in temperature increase the activity of aromatase.
It has been proposed  that temperature acts on genes coding for such steroidogenic enzymes , and testing of homologous GSD pathways has provided a genic starting point. The adaptive significance of TSD is currently not well understood.