This emphasis on bestiality being a actions rather then to be a doable sexual orientation can almost certainly be traced again to your seminal function of Alfred Kinsey. In his vintage 1948 e-book with Wardell Pomeroy and Clyde Martin, Sexual Actions inside the Human Male (W. B. Saunders), Kinsey https://dick43543.tinyblogging.com/the-smart-trick-of-dick-that-nobody-is-discussing-72103361