I think its a matter if nurture instead of nature. Sexual fetishes usually happen when someone identifies something in our childhood as arousing usually associated with some sort of bonding or trauma. I think people probably had these fetishes as society started becoming more structured. Personally I think fetishism started in the ranks of monarchy, where more privilidged people had time to induldge in different practices as everything for these people weren’t as survival/hardship focused as peasants would endure. For instance, a boy growing up might have tickled her sisters or babysitters more often as they had more time being attended to, thus they developed these fetishes psycologically. Anyway those are just my own weird thoughts. Take them with a grain of salt.