The average score would not always be 100. Lots of factors. When i was at u neefoundland professors were always asking why newfie children tested out so high. Some would be cultural,.slme financial opplrtinity, enriched environment. Lots would be genetic..and what traits of intelligence the test was measuring. There are many types of intelligence that just dont get measured but are very important oe were to our ancestors..throwing a spear,.weaving a.waterproof basket, memorizing the genealogy of hundreds of generations. And the harsher the environment the more natural selection is going on. But it would not necessarily select for intelligence,,could be disease resistance, ability to conserve fat or whatever.