ALL humans start out as female.

Ewww Biology. The first subject I dropped upon reaching grade 8 back then. 

A few weeks after fertilization, the initial appearance of the human fetal genitalia is basically feminine: a pair of "urogenital folds" with a small protuberance in the middle, and the urethra behind the protuberance.

In typical fetal development, the presence of the SRY gene causes the fetal gonads to become testes; the absence of it allows the gonads to continue to develop into ovaries. Thereafter, the development of the internal reproductive organs and the external genitalia is determined by hormones produced by fetal gonads (ovaries or testes) and the cells' response to them.

If the fetus has testes, and if the testes produce testosterone, and if the cells of the genitals respond to the testosterone, the outer urogenital folds swell and fuse in the midline to produce the scrotum; the protuberance grows larger and straighter to form the penis; the inner urogenital swellings swell, wrap around the penis, and fuse in the midline to form the penile urethra.

If testosterone is not present, normal female development continues, with the development of a perineal urethra and the formation of a uterus, clitoris and vagina.

The M�llerian ducts, which are paired ducts of the embryo which empty into the cloaca, and which develop into the upper vagina, cervix, uterus and oviducts; in the male they disappear except for the vestigial vagina masculina and the appendix testis.

Because of their common origin in fetal anatomy, a number of male and female anatomical features are said to be homologous; for example, the clitoris and penis are homologous with one another, as are Skene's glands in females and the prostate gland in males.

Most of the time, the result of fetal genital development follows the stereotypical male or stereotypical female development path. However, in a small but significant minority of cases, the path of development follows an intermediate or other pathway, leading to what are called "ambiguous genitalia", one condition of those known as intersexuality.

salams,

StarWish624 wrote: Before this, they are female, as the "X" chromosome is 3 to 1( XX/XY), over the "Y" in a male.

You're such a frikin ignorant!

The mother has XX, and passes one of them on to her oocyte (egg cells). In this case it's a 100% sure it's gonna be a X.
The father has XY, and he too passes one of them on to his spermatocyte... Here it's 50/50 whether the spermatocyte will contain an X or Y (meaning that males decide the sex of their offspring).

The 1 (SINGLE) X from the oocyte then splices with the X or Y from the spermatocyte to create the zygote... Now the Zygote will either be male or female, even though they will undergo exactly the same procedures for the first few weeks. But the sex of the fetus was decided even before the spermatocyte entered the oocyte - it was destiny, you might say.

Now even though this doesn't explain nipples... Well nipples are "created" long after the first few different changes between male and female fetuses begin, so there's really no explanation for their being present, other then they are a useless relic from the obsolete females.

And no, humans probably WON'T develop BACK into 1 sex... Actually more likely to develop into MORE sexes (1 species of fungi has over 200 sexes, now THAT'S what I call a tough dating scene ^^)
Now, one of the reasons for deteriorating sperm quality in men, is our worsened enviroments... Even seat heating in your car is "killing your troopers".

Now back to you StarWish... If you EVER speak on a biological matter without doing research first (NO! Asking 1 friend does NOT count - If he's a moron then you become one too!)
- else I'm gonna have to beat you down with a old peanut cracker