My default presumption on nature vs. nurture is that the environment counts for a lot. I usually start off assuming that nature and nurture each account for about half.
On the other hand, numerous intensive students of the scientific studies scoff at my baseline assumption that the environment is responsible for 50% of the variance, arguing for genetics being responsible for 60% to 80% of variation.
Am I just being cautious?
But I suspect that if you can look across history as well as geography, environmental changes can be substantial. For example, South Koreans today score dramatically higher than their grandparents on both IQ and height.
My rough guess, inspired by James Flynn’s discovery of the Flynn Effect, is that the environment often matters more across time than across space, which makes it harder to research because few researchers can wait around for a new historic era to see if that turned out to matter.
To take one example, we can study identical and fraternal twins raised apart in space. Usually, the results of twin studies suggest nature matters more than the conventional wisdom would suggest and nurture matters less.
But … until cloning comes along, we can’t study twins raised apart in time. My suspicion at this point is that it does matter what historical epoch you are nurtured in. But I don’t know how to test that.