The equal number of male and female human babies is primarily due to the mechanism by which sex in humans is determined. Females have two X chromosomes, and males have one X and one Y. Since each human zygote will always get an X from its mother, and it has a 50 percent chance of getting an X from its father, it will have a 50 percent chance of being female. Likewise, each human zygote will have a 50 percent chance of getting a Y chromosome from its father and have a 50 percent chance of being male. Thus, the one-to-one ratio of males to females in humans.
