Subsistence farmers have low income. That is an incontrovertible fact, they are the people making around $2 a day in real terms. Interestingly, they're concentrated in the countries with low average IQs.>>10471658
Ah yes, the 'intelligence can be anything I define it to mean' fallacy. It reminds me of the IQ-denialists who maintain that Africans have a very good intelligence... for living in Africa, one of the more racist things I've heard.
How can you possibly say that because an engineer isn't a very good subsistence farmer, both are equally intelligent (or differently intelligent)? You don't need to be intelligent to work out subsistence farming, merely do what your parents did. I recognize that these people develop sophisticated knowledge of food-treatment, developing multi-stage processes to get the cyanide out of various plants. This still isn't intelligence, merely tribal group knowledge.
IQ is culture-blind, pattern recognition of simple shapes. The tests work and they measure abstract thought, which, as the last 5000 years have shown, is pretty damn important.