Clinicians describe the deep, narrow interests in autism as “obsessions,” but a more positive description might be “areas of expertise.” Sometimes the area of expertise a person with autism focuses on appears not to be very useful (e.g., geometric shapes, or the texture of different woods). Sometimes the area of expertise is slightly more useful, though of limited interest to others (e.g., train timetables, or flags of the world). But sometimes the area of expertise can make a real social contribution (such as fixing machines, or solving mathematical problems, or debugging computer software).
My guess is that in autism, something is turned off that should be turned on. This allows the rest — in particular, the rest of what motivates us — to be seen more clearly. Everyone has a tendency toward expertise, says my theory of human evolution. Why everyone? Because everyone suffers from procrastination and the tendency toward expertise is the tendency that causes procrastination: It’s harder to do something new than to do what you did yesterday. Back in the Stone Age, this tendency toward expertise caused different people to do different hobbies, and become good at them. This was the beginning of occupational specialization.