http://www.unz.com/jthompson/the-7-tribes-of-intellect/
Tribe 1 “High Risk”
These are the least able 5% of the population. In a town of 10,000 persons these would constitute 500 citizens. Learning is slow, so all intellectual achievements take a fair bit of time. Since all lifespans are finite, and for this group lifespans are shorter than average, many skills are effectively out of reach because it is very unlikely that they will ever be learnt. Of course, some learning always takes place, because everyone can learn, but in their case the pace must be slow, the materials simple, and the steps carefully supervised.
Lifespans are more than 21% shorter than average, and they are more than 50% more likely to be suffering psychological difficulties than average. They are most at risk of all health problems, and all the problems of life.
These people are “high risk” because they make unforced errors and because they are at risk of being exploited by the unscrupulous...
Tribe 2 “Uphill Battle”
These are the next 20% of the population in terms of ability. They would be 2,000 citizens in the town of 10,000 inhabitants. Learning is somewhat faster, and achievements are of better quality. Learning varies from the slow pace, simple materials and careful supervision already mentioned previously, to very explicit, hands-on training. They tend to credulity, belief in god and superstition. They can locate the intersection of two streets on a map, identify two features in a newspaper sports story, perhaps calculate the total cost of purchases listed in a catalogue, and draw inferences from two identifiable facts and deal with some distractors.
Vocabularies are somewhat larger, computation includes some multiplication and division. In terms of reading they will enjoy a little more depth in terms of content. Employment opportunities include simple assembly and packaging tasks, food preparation, assistant roles in caring professions. They can use some checklists, and procedural guides. The armed services will probably not recruit them, because many of them will take too long to train.