pervert「逆さまにする」、-s「過去分詞格」から。
Perversions are defined as unnatural acts, acts contrary to nature, bestial, abominable, and detestable. Such laws are interpretable only in accordance with the ancient tradition of the English common law which ... is committed to the doctrine that no sexual activity is justifiable unless its objective is procreation. [A.C. Kinsey, et.al., "Sexual Behavior in the Human Male," 1948]