The fact of gaining feminine features. The phenomenon manifests itself at the individual level, and at the historical level as well. At the individual level it turns a man to a shemale
or a ladyboy
and he ends up gay or not (he can also remain hetero and be attracted to he-females, or be bi). At the historical level it has to do with the emergence of feminine priorities in the world, and with the global increase of the ordinary (rather than political) power of women.