The article linked above is where I should've emphasized this:
"Westerns have lost 14 IQ points on average since the Victorian age, according to a study published by the University of Amsterdam last year.
Jan te Nijenhuis thinks this could be because intelligent women tend to have less children than women who are not as clever, The Huffington Post reported.
The perceived link between IQ and fertility is a very contentious one.
Dr Nijenhuis studied the results of 14 intelligence studies conducted between 1884 and 2004 to come to his conclusion.
Each study measured peoples' reaction times - how long they took to press a button after being prompted.
It is claimed that reaction time mirrors mental processing speed - so it reflects intelligence.
They found that visual reaction times averaged 194 milliseconds in the late 19th Century, but in 2004, they had increased to 275 milliseconds.
This would suggest that people have become less intelligent, they said."
That's not really how we measure IQ though. Although reaction time is a measurement there are verbal, spatial and mathmatical skills emphasised in the standard test (Stanford-Binley test). I don't know much about IQ but I took that test twice with years in between with a psychologist. I got 98 and 101 in the tests and with a +/- 5 margin it means my IQ is somewhere between 96 and 103. Which is in the "normal" IQ spectrum.