Well i think humans have gotten smart enough to question their sexuality. In fact we have been doing it for years. In Rome it was commonplace for men to have a second (usually male) partner as what is more manly then marrying a man? In Mesopotamian mythology and underworld myths there have been asexual characters as well. Same with Greek mythology with many characters having gay relationships, we have been doing these things for centuries.

Nothing can truly be 100% anything. I believe that homosexuality is mostly nature, but there is some nurture involved.