[IvyMike]

First of all, there's not enough data to be statistically significant in any of my ramblings, so it's all kind of hand-wavy and I apologize for that.

But my general feeling is that there used to be a few "powerhouse" countries and institutions that dominated, but that has been changing for many years. There's a lot more diversity these days. So I think kiyoto's point speaks to the changes there.

In 1950, it would have been pretty inconceivable that a woman from Iran would have had the access and opportunities to contribute to mathematics in a way that would have earned a Fields medal; in 2014, it's a first-time feat; hopefully, in the future, it quickly becomes mundane.

[conjectures]

"not enough data to be statistically significant"

^suspect this is incorrect.