I think it's not just biological. Or rather that biology is affected by upbringing. Classical conditioning and all that. If you are traumatised by certain people as a kid, seeing someone who reminds you of your abuser can cause your whole body to seize up and feel sick. That's a biological reaction. But it's not one you were born with. It's one you developed through your interactions with the environment. Why can't attraction be the same way? A mixture of preprogrammed feelings you were born to have (like being straight or gay) and associations you developed through your life experiences?