As a disorder, ADHD has both environmental and genetic/structural causes. Diet, parenting techniques, classroom design, these factors interact with the structural differences I've highlighted elsewhere.
Maybe they are an evolutionary adaptation, hell, they have to be. But human programming is overrated. We can and should train ourselves away from our programming, especially when it is causing real trouble in our lives. What are parents supposed to do? Have their kid drop out of public school or simply not learn anything? Quit their jobs and home school? We have to be realistic. The most realistic solution to ADHD is a two-pronged approach, medication and lifestyle changes, and it should be based on actual observations of a child's behavior, in accordance with ICD-10 criteria.
A good parent does what will make their kid succeed in the world as it is, not simply according to the world as they want it to be.