Can animals change sex?

Can animals change from male to female and female to male? Which animals change sex and why? How are changes in the environment causing more animals to change sex? For free home activities sign-up at www.WhoSmarted.com   See omnystudio.com/listener for privacy information. See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.