Asexual to sexual reproduction? How?

My assessment would be:In a hermaphroditic species it can be an advantage to be male. Males invest fewer resources in the reproductive process itself, so a successful male can produce more offspring than a hermaphrodite.But once there are a lot of males around it becomes an advantage to be female. When competition for the male half of the reproductive equation is fierce it can pay to stop competing in that arena and become purely female.So when the species is predominantly hermaphrodite there is an advantage to specialising in the male role. As the proportion of males goes up the advantage of performing as a male goes down, until it becomes worth ceasing to invest resources in it at all and specialise as a female. (And if the proportion fo males goes down the advantage of beign male goes back up).Of course this is hypothetical and I don't claim any special knwoeldge but this view is plausible based on what I do know.