I did mention nature. However, if one never encounters their particular kink (trigger) at an impressionable time in their lives (timing) how would it form? We are programmed to enjoy sex (hormonal) and hormones influence us (pituitary gland/hypothalamus) via a complex interaction of epigenetics, ecological, social, historical, socioeconomic, nutritional, cognitive/motor functions.... it boggles the mind. Plus, we can build tolerance (physically and psychologically). If you're interested in the subject, search Dr. R. Sapolsky on YouTube. He was my inspiration and one of my professors. He really has a way with the subject. He was the chief reason I went the bio/psych rout. You can also look into chaos theory and [strange] attractors as they pertain to biological systems. Really heady stuff.