There are certain afflictions so common that one can't help but think they must have some evolutionary benefit. The most commonly cited example of this phenomenon is sickle cell anemia. When the gene for this disease is present only in recessive (heterozygotic) form, it provides protection against malaria. However, when the gene is inherited from both parents, the homozygotic condition results in the red blood cells assuming a sickle shape which can lead to all sorts of unhealthy complications.
There are other syndromes which are so common that one has to think they, in one way or other, must have conferred some evolutionary benefit.
Two such are Attention Deficit Disorder and Attention Deficit Hyperactivity Disorder. These are so widespread that one would think they must have some potential benefit. Otherwise they would have disappeared long ago.
(I sometimes think I suffer from it; in school I always had a hard time keeping my mind on whatever the professor was droning on about. I have that trouble in ordinary conversations now. And, come to think of it, this blog-without-a-unifying-theme may actually be ADD writ large.)
So -- when your attention races from one thing to another, what is the benefit?
After giving the matter some thought -- for as long as I could concentrate on the subject, anyway -- I've come to the conclusion that it's tied into alertness. If you concentrate too much on just one thing, you may be less likely to notice when a lion is sneaking up from behind to ambush you. You actually want your attention to be easily distracted by whatever is happening in your vicinity, whether that be a potential predator like a lion or potential prey like a careless deer.
Having ADD may also have helped one to be well-rounded in a way that would have helped you survive back in the hunting and gathering days. To thrive in that environment, you must be interested in finding out about all sorts of things: how to hunt, how to trap, how to avoid dangerous animals, which plants are edible, how to find a potable water source, how to make clothes out of animal skins, etc. These weren't fun hobbies, but necessities. If you were incredibly good at knowing which plants were edible, but at nothing else, you would not have lived to pass on your genes.
Being a specialist today can result in making a good living; in the old days it might have meant not living at all.
One of the most charming guys I know has a pretty obvious case of ADD. He knows a lot about a variety of subjects, and expresses great enthusiasm about many of them, which is part of his charm. A wide-ranging curiosity is supposed to correlate highly with intelligence; but he wasn't a particularly good student, undoubtedly because of his ADD. He once told me that he ranked towards the bottom of his engineering class; he said this in a mildly mournful way, as if this proved that he wasn't that smart. But one of the first things you notice about him is that he's always very much aware of whatever is going on around him, much more so than most people. I would be willing to bet that he has more general knowledge, and probably a higher IQ, than most of the students who ranked ahead of him. And survival at any time over the past four million years of human evolution -- right up until around two or three hundred years ago -- had less to do with getting all A's and more to do with familiarity with a wide range of survival skills.
The nature channels often show lion cubs gamboling about, play-fighting with each other, exploring, chasing after rodents, and so on. The narrator will usually point out that this is how the young animals learn and prepare themselves for their adulthood. The way these cubs are constantly on the move, you might almost say they had ADHD. But it's also clear how this benefits them: while curiosity may have killed the cat, a lack of curiosity might well eventually kill it too. In a real life situation, you actually learn and observe more by being active -- maybe even hyperactive.
Similarly, the instinct in young boys to be like the proverbial cat which wants to be on the other side of every door seems to be, well, instinctual. This is how young boys -- and to a lesser extent, young girls, who are diagnosed less often with ADD -- have always learned. At least up until the past few hundred years.
We didn't evolve for four million years to sit in a classroom for seven hours a day, five days a week. In fact, we evolved to do all sorts of things -- such as rape and murder and steal -- which aren't exactly condoned behaviors today. But when trying to explain human behavior, it's always more helpful to think in terms of the four million years we spent hunting and gathering rather than the few hundred years we've spent in an industrial/technological society.
Anyway, that's all the attention I can devote to that subject.