Unless circumstances never change, there's always value to a population in having a spectrum for any trait. It's also likely that the specific characteristics t

Unless circumstances never change, there's always value to a population in having a spectrum for any trait. It's also likely that the specific characteristics that best position individuals for success as modern white collar workers were optimal for 99% of the evolutionary timeline of human existence. If mild to moderate ADHD offers an advantage in a high mortality setting, the loss of individuals with more extreme symptoms isn't going to make much of a difference in selection pressure. (sickle cell anemia is an extreme example of this)