>Sex isn't always a win; some species reproduce by selfing and some
>of those seem to have been around for quite a while.
And some switch mid-stream [many, in fact, are fish], depending on their
circumstances. A brief, brisk treatment is the section `Why Be a
Hermaphrodite?' in George C. Williams' accessible little book PLAN &
PURPOSE IN NATURE (Science Masters series, 1996). He notes: `there are two
kinds of herm., the *simultaneous* and the *sequential*.... As a general
rule, an org, will be a simul. herm. if the adaptations for one sexual
function can also serve the other...' In the sequ. varieties, `change
always conforms to what is called the *size advantage* model'. Male-first
herm.s use *scramble competition*, while female-first herm.s always use
*contest competition*. I have a complete proof and explication of all
this, but the margins of my emailer are too small to give them.
Damien Broderick