We can observe microscopic critters doing the very things that would have led to sex anytime we want to exercise a microscope on pond water. Many soft-bodied micros engage in genetic exchange through direct genetic manipulation that falls short of being procreative, but is very suggestive of sexual gamete exchange. Nice try, however, since these were not sexual creatures you need to show how such a thing happened. Further, since single-celled creatures are not sexual, and sexual creatures are multi-celled you first have to jump into multi-celled creatures (which do not exchange genes) or propose a way in which both multi-cellularity and sexual differentiation occurred in one gigantic jump. Sounds like a miracle to me.
Nice try, however, since these were not sexual creatures you need to show how such a thing happened. Further, since single-celled creatures are not sexual, and sexual creatures are multi-celled you first have to jump into multi-celled creatures (which do not exchange genes) or propose a way in which both multi-cellularity and sexual differentiation occurred in one gigantic jump. Sounds like a miracle to me. Sounds to me like sexuality is a fairly obvious way to regularize the process of genetic exchange we observe in, for example, mushrooms, as they change from a chemically co-ordinated community into a physically congruous creature.