pprof’s 2008 website

Imagine a world inhabited by male and female beings. Imagine a world where these male and female beings, at a certain point in their lives, form some sort of stable relationship and have little babies - male and female - born to them. So far, it sounds rather dull, but…

These male and female beings differ from us in that it is not merely the women who carry the babies. In fact, in this world, the baby’s sex is identical with that of the parent that carries the baby. Women only give birth to little baby girls and men only give birth to little baby boys. Also, when a man and a woman have sex, each of them is equally likely to get pregnant.

Now, if this world was us, how many boys would be born each year? What would the proportion be between the number of girls and boys? How many single fathers would there be? Would people care more about who they sleep with? Would guys have abortions more often than girls?