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Hi Sara - I think you are trying to make the question too complicated. Some species have extremely different morphology between males and females and others are very similar. If the genes that give different morphology/behaviour give that individual a better chance of breeding than others in the same niche then it has a greater chance of passing that trait on to its offspring... and so on. We don't wonder how a male Pheasant could have evolved to be such a different colour to the females ... and in the same way some flies have different behaviour that helps their genes continue. :)

Also remember that "species" is a human concept but in almost every species the individuals are not clones, they have slightly different genes that express slightly different traits ... but they all share a common ancestor that would look virtually indistinguishable from the current generation.