Arthur Georges is an international expert on the evolution and ecology of reptile sex determination. His proposal that genetic and environmental sex determination represent ends of a continuum have revolutionized understanding of how the complex thermal environment of nests dictates sex in reptiles. His recent work on sex reversal reveals molecular mechanisms of temperature sex determination and provides astonishing insight into the evolution of TSD and GSD, and how environment interacts with genotype to determine sexual fate. His work redirected thinking on how climate change might impact reptiles with thermolabile sex, and stimulates a rethink on how reptiles survived past climate changes, and how human activities constrain their ability to respond to future challenges.