Critics began to challenge the validity of the IQ in the 1950s and ’60s. They noted that the IQ tests were racially and culturally biased.
Exposure to leaded petrol as a child has been linked to an average IQ drop of 2.6 points among US adults, increasing to 5.9 points among those born in the mid-to-late 1960s
The idea that some racial groups are, on average, smarter than others is without a doubt among the most discussed (and debunked) “taboos” in American intellectual history. It is an argument that has been advanced since the days of slavery, one that helped push through the draconian Immigration Act of 1924, and one that set off a scientific firestorm in the late 60s that’s hardly flagged since.
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