Totally off-topic, but in your fair world wouldn't we also be able to have a perpetual motion machine?

Another effect that might play a small role here: the school year in the US typically ends in May, and school teachers might have tried to 'time' their pregnancy in order to have a baby after school let out for the summer, and so have at least three months with their baby before the next school year started.

This was the case in my family: my mother was a teacher, and both my sister and I were born in May, just as school let out (I'm speculating about cause and effect, however).

Off on a tangent... You mentioned Mathematica, I've found at my University that many students got their first introduction to programming there, and continue to use it in research, in tasks it is arguably not well suited for. Mathematica is a good way to visualize math, and perhaps a decent intro to programming, but I'm very surprised to frequently find it used for extensive Monte Carlo simulations where floating-point calculations would be much faster and sufficiently precise.