dberne:

does not mean there is no problem. Sickle cell anemia comes immediately to mind. Having one but not two genes protects in malaria. But having two genes results in a severe illness that often shortens life. The genetics behind ADHD are poorly umderstood. A "mild" case may indeed be advantageous, but a more severe case would not. Imagine being inattentive to the environment when the environment has big hungry creatures ready to harm you (e.g. "Watch out for that snake!")

You kind of misunderstand how ADHD (or attention in general) actually works. A person with ADHD is actually going to be more attentive to dangers and opportunities in the natural environment than a neurotypical person. People with ADHD may have a hard time concentrating on lectures or on typing up quarterly reports, but in active sports or in nature, they can do very well. A person with ADHD will see that snake in the grass or the big predator in the tree before you do.

ADHD brains are very well adapted for a hunter-gatherer lifestyle. In fact, that's what all human brains are adapted for. The kind of lifestyle we live in industrialized countries today is actually harmful to us in many ways because it doesn't "mesh" very well with the human cognitive makeup.

Our physical and mental evolution has not kept up with the pace of change in our technology and society. There are ways to change our lifestyles to be more friendly to our brains, but it requires us to realize that the way we live is not "normal" as far as our biology is concerned.