Is it normal to lose genre-specific arousal due to desensitization/boredom?
The title is a mouthful, so I'll just clarify a bit.
Desensitization is a psychological term which refers to a loss in responsiveness (or in this case arousal) from repeated "stimuli" (pmo). By "genre-specific" I'm referring to porn genres and sexuality.
I've masturbated quite heavily over the past 6-8 years, but during this time the type of porn which aroused me has made quite a massive shift. At first the typical straight/lesbian stuff was enough to get me pumped up, and that lasted for about 2/3 of this period. Then, I could tell my interest was decreasing, so I began exploring more and more novel/strange types of porn (shemale, gay etc) which turned me on a lot more. I still masturbate to straight stuff about 50% of the time, but it just doesn't do it for me anymore.
Is this normal? Is it possible that heavy exposure to vanilla porn has warped or altered my sexual preferences, or am I just expressing uncovered/innate sexual tastes?