Leaded gas? Can’t be that, because the numbers went down between the first two generations in the 20th century, and leaded gas wasn’t outlawed until the late 20th century. But it’s still probably environmental, perhaps something like childhood nutrition.
Leaded gas?Can’t be that, because the numbers went down between the first two generations in the 20th century, and leaded gas wasn’t outlawed until the late 20th century. But it’s still probably environmental, perhaps something like childhood nutrition.