When I contemplate ADHD, birds often come to mind, scanning their near field for potential dangers with almost extreme vigilance, changing their position and moving to safety at the slightest impulse.
In humans it will be very similar, especially in the hyperactive type, except that human culture offers an almost unbelievable variety of stimuli in addition to eating, digesting, reproducing and communicating about these things, and also requires adaptations that run counter to our natural impulses.
In many cases, people will intuitively choose the course of action with the highest dopamine yield, and in the end they will totally exhaust themselves because they will sooner or later overload the dopamine system due to the extreme availability of triggering stimuli.
ADHD is thus an adaptation to conditions, presumably a more archaic form of early man, mindfully moving in a dangerous wilderness and reacting to real dangers.
The fact that it is considered a maladaptation results from the fact that the cultural requirements cannot be fulfilled in the idealised sense by the ADHDer, sit still, be concentrated, behave conformably.