I should really be sleeping. LOL. But really very interesting MSU, thanks.
Better than a National Geographic article LOL
On social insects, I was an ant fanatic once. I built several antfarms and read all I can about them. This brought back a LOT of memories. hehe. Just something to add I guess. In primitive ants, females are less differentiated from each other. The ponerines I think, and bulldog ants. In which, every female is fertile, and there is no queen-worker differentiation in the females. I'm not sure about wasps and bees, but I think the solitary ones also have males which do not die immediately after mating (the males in more advanced social insects often die after the 'nuptial flight' because of devolution of their feeding capability anyway - they can't eat by themselves).
Also that of limpets and groupers which change their sexes as they age. In these instances, sex is determined by environmental factors rather than heredity, do all of them have more or less the same types of chromosomes in each individual? i.e. no male-determining/female-determining chromosome, and the sex determination is based on switching certain genes off and on either by will or by environmental factors.
Thus differing from sexually dimorphic species which have gender specific chromosomes are doing this by the fact that the gender determining chromosome is somehow 'dominant' over the other. Like Y in humans since Kleinfelter's are always male and Turner's female. Though again, as you said, birds and reptiles do seem to be based on the presence of 2 Z's. Bleh too complicated. Don't answer that, they're more like rhetorical questions LOL
And yeah I do see the role of sexual dimorphism in evolution. Secondary sexual characteristics for example. How they develop would be pretty interesting to study, especially in species in which males and females vary greatly in their form. (Birds of Paradise, Peafowl, Anglerfish, Siamese Fighting Fish, Swordtails, etc.)
Hm... even plants are sexually dimorphic at times, but in a different way than animals, so not probably something inherited from the same primeval ancestor with dimorphism, different evolutionary paths I guess. So younger than protozoans, fungi, and molds.
I googled a bit. And it seems rotifers show sexual dimorphism already. So pretty ancient indeed.
Anyway, have to sleep. Thanks for the interesting posts! ^_^