Iain Banks' Culture series (sci-fi novels) explores this subject in a way I enjoyed greatly. "Biologically, the Culture's citizens have been genetically enhanc

Iain Banks' Culture series (sci-fi novels) explores this subject in a way I enjoyed greatly. "Biologically, the Culture's citizens have been genetically enhanced to live for centuries, and have modified mental control over their physiology, including the ability to introduce a variety of psychoactive drugs into their systems, change biological sex, or switch off pain at will. Culture technology is able to transform individuals into vastly different body forms but, for unclear reasons, the Culture standard form remains fairly close to human."