[streptomycin]

It's roughly the same as the change that happened when we stopped using leaded gas, which seems to have had a huge affect on society. http://en.wikipedia.org/wiki/Tetraethyllead#Toxicity

Also it's just one relatively simple thing. Imagine we find several things that can all increase IQ by a couple points...

[cheatsheet]

I've never gotten my IQ tested, but when I read about studies like these - they usually demoralize me from fear of competitive behavior. I think this leads to low self esteem, and the imagining that I have a low IQ (high marks through schooling and post graduate education, MSc, possible imposter syndrome) as my default attitude. It can be a self defeating attitude, but what it usually does is make me argue with people about IQ tests, and explain why they are not necessarily indicative of intelligence, individually or globally.

I can imagine that merely the act of measuring IQ has significant effect on the population. I can not imagine a population that exists without it, but I imagine it would also have a huge effect on society, as you similarly hypothesize about the 1-3 point increase across the population globally.