Well to be honest the iq test has always been kind of bullshit imo. It changes with your level of education. In HS mine was 120 and now it's 143 (edit: I actually took that test 4 years ago and 3 years ago I had a brain tumor that left me with seizures and I have definitely suffered cognitively because of that so its probably lower if my memory and focus are any indicator). The test itself doesn't even measure useful cognitively profound abilities and if it did we'd all be near the same. It measures everything as a flat value. There is no value for each type of cognitive ability and most of it is skills you've picked up through life and education.

So when you look back at our great grandparents, take me for example, I'm part native hawaiian and my great grandparents were literally living in a shack on the beach. Their lives consisted of catching fish and fruit and sugar cane farming I don't even know if they could read before my grandparents started school. So of course their iq is lower. I mean hell you can't even take the iq test if you can't read. So I don't think the brain changes that we have are responsible for our higher iq points. I think it's availability to information, the more you have and contemplate the smarter you'll be. Pretty straight forward I think. Higher nutrients and regularly available food is helpful as well obviously.