Sci-fi can be succinctly defined as speculation, whether based on established scientific facts or on logical pseudo-facts consistent with the framework of the fiction in question, involving smelly green pimply aliens furiously raping or eating, or both, beautiful naked bare-breasted chicks, covering them in slime, red, oozing, living slime, dribbling from every horrific orifice, squeezing out between bulbous pulpy lips onto the sensuous velvety skin of the writhing sweating slave-girls, their bodies cut and bruised by knotted whips brandished by giant blond vast-biceped androids called Simon, and written in the Gothic mode.
Galen explains clearly, if less succinctly, in De Causis Procatarcticis (2nd c. A.D.), VI. 63–65:
Phrenology's fundamental assumptions remained constant throughout the history of the movement. They were succinctly stated by George Combe as consisting of the folowing three "fundamental principles': (1) That the brain is the organ of the mind:;; (2) That the brain is the aggregate of several parts, each subserving a distinct mental faculty; (3) That the size of the cerebral organ is, ceteris paribus, an index of power or energy of function.
Put succinctly, the question is this: How does a generation with absolute knowledge of felching, donkey punching, and the dirty sanchez maintain healthy sex lives?