I wonder if the Flynn effect could be more about our cultural environment then our chemical environment.
In 1900 lots of people lived with low access to information or highly sensory stimulating environments. By 1950 there was a lot more stimulus and info. TV, comic books, color movies, rock & roll, fear of nuclear armageddon. By 2000 we're overloaded. Cable TV, computers, cheap and rapid long distance communication, fear of climate armageddon. Maybe the cognitive load has just become too much. Two beers might make you better at darts, but 20 won't.
In 1900 lots of people lived with low access to information or highly sensory stimulating environments. By 1950 there was a lot more stimulus and info. TV, comic books, color movies, rock & roll, fear of nuclear armageddon. By 2000 we're overloaded. Cable TV, computers, cheap and rapid long distance communication, fear of climate armageddon. Maybe the cognitive load has just become too much. Two beers might make you better at darts, but 20 won't.