I got my original answer from
All humans begin life in the womb as females. If no Y chromosome is present in the foetus, then the embryo will continue to develop as and be born as a female. If there is a Y chromosome present in the embryo, the male sex hormone testosterone restricts the full development of breasts to just nipples, the labia fuse to become the scrotum and clitoris develops fully to become a penis. If the Y chromosome prevails in producing a male, this is not done without a fight. Male babies are weaker as a result than female ones, occounting for the slightly higher death rate in male babies.
Are you really a bio major? thats pretty cool that you learn that in bio though.