It takes something extra (androgens) for males to differentiate as male around the
sixth week of embryonic
development. Once androgens (most notably, testosterone) kick in, the vagina seals up and your penis and testicles form. That line is the scar left behind when everything seals up. BTW: all birds and reptiles are just the opposite: male is the default setting.
So you see, whether biologically female or male, we're all the same under the skin. Dr.