lets step into our time machine back to tenth grade biology, to a little thing called the punnett square. it state that even a hermys possibility of male and female reproduction is 50/50 to give it maximum reproductive chanves. because after all charles darwin stated that the species that is doing the best is the one that has the most surviving offspring
but we aren't speaking of a true hermaphrodite here, we are speaking of an "intersexed" plant. a true hermie has both male and female flowers; an intersexed plant on the other hand, is a female which, usually later in flowering, will throw out one to a few "naners"; which are not seperate male flowers, instead they are single pollen stipules which come out of calyxes (the vag). dig around; some more experienced people than i were talking about it in advanced cult. saying that almost
all females will intersex if left flowering too long....self preservation maybe??
edit* also, this would still fit into your darwin survival example: if the plant were to pollinate itself with a little ?female? pollen, then it would still ensure survival; possibly even better survival due to the fact that next growing season there would be many more females around; if there is one male around that year, it could, in theory, pollinate all of those females, resulting in more seeds for the third season than would have been there had the first one not produced only female seed. hope that makes sense to you, but just my thoughts