I woke up this morning to the thought that yes the male female split in humans is all over the place, no doubt about that. Does this make our sexuality fluid tho? No, it doesn't seem to, not as an individual it doesn't. That isn't what we experience, is it. I can go to sleep with confidence that I am not going to wake up as a lesbian one morning. Let alone wake up as a man, gay or straight.
If you view humanity as one vast being then yes it is all over the place, but on an individual level it doesn't seem to be that way at all. Sure it develops as we mature right through our lives, but it doesn't change quarters.
I know this is true for straights but it also looks to me to be true for all of us, including bisexuals - I mean does anyone know anybody who really has gone from having same sex attraction to not having it?