"Right. I understand that part. Same reason why professional cyclists wear helmets."
But this is simply not true. As a person who follows the sport of cycling I know that many professional cyclists will use helmets only during races (because they are required to), during training they won't.
My thought on this is that there is either something wrong with this chart or the IQ test that produced it. It is possible that in a perfect world where everyone had an equal opportunity, that the high IQ ppl would tend toward high education and science in particular, and that low IQ ppl would tend toward manual labor...
But I doubt it, and we don't even live in that would.
This chart is measuring something other than IQ, perhaps the amount of education in math...
It reminds me in an uneasy way of A Brave New World where ppl intended for menial work had their IQ lowered before birth by oxygen deprivation...