In this episode, Dr. Huberman discusses how hormones such as testosterone and estrogen and their derivatives impact the early development of the brain and body and their maturation. He reviews published data on environmental factors shown to powerfully alter hormone pathways in animals and humans and the effects of cannabis, alcohol and cell phones on testes, sperm, ovaries and hormones. He describes the predictable relationship between genes, beard growth and balding patterns, and the importance of estrogen for brain development in people of all chromosomal sexes. Finally, Dr. Huberman discuss how the hormones we are exposed to in the womb shape the relative length of our finger digits, the sounds our ears make (yes, you read that correctly), and how those correlate with people’s self-reports of their sexual preferences. As always, basic information and tools are discussed.