Why are the IQ's Mensa levels when unlike mensa we don't have a cutoff? This is a *strong* self-selection effect.
Hunter-gathering probably needed skills that are harder to AI-replace *for the common individual* even if farmer societies can use their greater numbers to accumulate more technology. This is because farmer societies move around less and have more specialized labor, making life require more narrower tasks and less general problem solving. That latter is what we call "intelligence". The 21st century is reversing this trend rapidly with automation.
Farming existed almost all over the world for long enough for natural selection to matter but not enough for our DNA and cultures to completely "forget" life as a hunter gatherer. Modern society is (most likely) a mix of ~10 hunter-gather phenotypes to ~90 farmers. The farmer phenotype has a lot of less interest in asking "why". The "intelligence" difference between a person who asked "why" since age 3 and one who didn't is a result of massive differences in training. Same with any other talent such as violin.
No non-human animal species with a well-studied intelligence had a sudden transition in the "window" of ~10000 years ago that drastically changed the skills needed to get by.
The sample size isn't big enough: nearby countries are too strongly coupled with each-other. Regions are closer to independent. But the only major regions were Europe, Middle East, East Asia, India, West Africa, East Africa, South Africa, and several in the new world. It's hard to form statistics around such a small number.
Of these, four enjoyed "top of the world" civilization status at some point in time: the Middle East + North Africa, Europe, China, and India. Mesoamerica lived independently until it got destroyed by Europe, so it is hard to place in a global hierarchy. This list is pretty random; there is no evidence for or against an "avoidance of the equator".
And it keeps moving. After the industrial revolution, the "top of the world" in terms of innovation moved from England to New York (Edison days) and most recently into the Silicon Valley.
But why does the king of the hill keep changing? So what breaks the technology/resource extraction/warfare feedback? It's basically crumbling infrastructure combined with regulatory capture at all levels of institutions. The trouble is the timescales are now so fast that the silicon valley is already elderly. There are 5 gas-tank apps. Many startups use the same recycled formula with social media, block-chains, "Uber for X", etc rather than addressing new problems. We already have to go to wherever is "next" (which may or may not be in the same physical area) if we want to use our skills in a young blossoming community.
How are measuring intelligence? Most of the WAIS puts machines far, far ahead of humans. This includes block design, arithmetic, digit symbol, anything that tests memory, etc.
Why do we care about intelligence? We actually care about "mental skills humans have that machines can't yet replace". Measuring this doesn't seem easy, especially if the WAIS favors machines so much.