is oily skin associated with acne or is that simply estrogen, cortisol, inflammation causing acneIt is not clear from your syntax whether you are asking
1) "how do we know these are androgenic traits?"
or
2) "why have males developed these caracteristics?"
1) antropologic analysis, common observations, blood levels to physical traits linkage.
2) men have always been the one executing hard labor: developing a thick skin makes it harder for external threats to penetrate the dermis. Oily skin keeps the skin moisturized in tough weather.