There's preliminary evidence for weak but steady selection against cognitive ability and/or educational attainment over the past century.

http://biorxiv.org/content/early/2016/05/05/037929

http://www.pnas.org/content/113/24/6647/F2.expansion.html

http://www.sciencedirect.com/science/article/pii/S0160289615...

https://jasoncollins.org/2016/07/22/kaufmanns-shall-the-reli...

The main driving factor seems to be educated people (and women in particular; some studies have found positive selection for men) not having children.