Evolution of human sexes?

Question

I say that XX--->XXY--->XY. If so, how?

How do you say that XXY are infertile? If they are infertile, what is the reason that they are otherwise healthy. Are they ordained just to live as for no reason? You can argue that only a sexually healthy individual can reproduce. But what if that they are all really fertile but ordained as virtually sterile by priest community in the name of gods? They can also produce sperms, by chance, normal ones, X or Y. My viewpoint: Asexual XX ---> (A)sexual XXY x Asexual XX ---> Sexual XX & Sexual XY... Why can't XXYs be remnants of sexual evolution. XXys can be unnoticed in animals other than human beings. Maleness and femaleness are just cases of dosages of Xs, as XX, XY, XXX, XXY,XYY,... We talk about a mother amoeba giving 2 daughter amoebae but why don't we argue XXYs as an intervening sequence for sexual evolution in all sexually reproducing animals? I just say that Y got added to XX as XXY ...?

Answer 1

Actually, you cannot get an XYY, it isn't possible. An XXY is formed when the sperm of an X and a Y invade an egg. The physiology of 'why' an X is an X and a Y is a Y is only recently been discovered and can be googled. As far as infertility goes, it all depends on whether the XXY has ovaries or not, and if so, if the eggs are fertile. It has nothing to do with social stigma, especially since many XXY's don't even know they are XXY's. There are more XX's that show masculine traits than XXY's that exhibit similar traits, because there are more XX's than XXY's.

Answer 2

Sexual reproduction evolved long before humans. Humans just it from the existing mammals they evolved from and they probably took it from other vertebrates they evolved from.

XXY humans (Kleinfelter's Syndroms) are infertile so it couldn't have evolved that way.