Centuries ago, wives were sometimes blamed for their inability to produce a male heir for their husbands. However, today we know that:
◦ it is the father who determines the gender of a child based on the chromosome he contributes.
◦ female children are heartier in utero and at birth and have a greater chance of surviving to their first birthday.
◦ the probability of having a female child is greater than that of having a male.
◦ the probability of bearing a son increases with second and subsequent births.