The so-called "marriage-squeeze". Earlier research has found a correlation between the sex-ratio (for age of marriage) and the amount of the dowry. 
A changing sex-ratio is often the result of a change in birth rate: men of a certain birth-cohort often marry women of a later birth-cohort.

And I really did copy/paste this to print it!

Here in Europe journalists and other experts have a straightforward explanation for the schoolshootings in the US: the right to own arms. Of course I believe all what these experts tell us. But then i have to conclude that the right to own arms in the US is limited to males. Is this really so? ;-0 
(BTW the big schoolshootings in Europe are always a little bit forgotten by our experts...)