The basic idea could be expressed as follows: give the exact same amount of water, sunlight, nutrients, etc. to two different trees, and the amount of fruit they will produce will depend entirely on their genes.
Likewise, make sure every kid has food, clean water, a home, medical care, schooling, etc. and then their differences in intelligence will depend entirely on their genes.
A perfect meritocracy would replace cultural class with biological caste.
It's a seductive argument, that overlooks, I think, an important factor:
Different organisms have different optimal environments for their best performance.
Let's go back to the tree analogy. If you equalize their environments, then their output (fruit) will depend entirely on their genetic input (genes). But what environment should be chosen?
A desert plant is ruined by too much water, a jungle one by too little.
It is far from an obvious proposition that the "ideal environment" as currently envisioned by Western social policy makers is indeed the optimal one for all members of our species.
A Norwegian and a Nigerian will both suffer if they are exposed to the sun too much or too little, but their optimal "sun exposure" points are different; a Pygmy and an Eskimo will die of starvation with too little food and of a variety of ailments with too much, but their optimal "daily colorie intake" points are different. Even members of the same population differ in what is good for them.
In Aristotelian terminology, "mean is best", but "mean" is not the same for all, and what is an excess for one is a deficiency for another.
It could be argued that current affluent societies do not enforce particular environments, but give the freedom to their members to choose their own. In a truly affluent society where anyone has the means to adopt whatever lifestyle is best for them, it will be the case that variation in any particular trait (e.g., intelligence) will depend on one's genes: Norwegians, Nigerians, Pygmies, and Eskimos may choose what is good for them, they are not forced to live in a suboptimal environment
That, however, is a mixed blessing because a free society is also a very particular kind of society that is not necessarily best for all. It could very well be that some organisms reach their optimum performance under compulsion, and I see no reason to think that kids (or adults) become excellent by doing what they want and not by following the instructions of those who know better.
For example, kids learn to read and do multiplications by being forced to do a lot of tedious repetition. In a free society, an adult is largely free from compulsion, but that does not mean that he will choose to do what is best for himself.
In a free and affluent society everyone has the potential of having the best possible physique and the best possible cognitive ability that their genotype will allow: "money is no object." But, as we well know, few people use their freedom to achieve their full potential.
- Fix the genes (as in clones or identical twins) and all variation is due to the environment
- Fix the environment and all variation is due to genes
- The eugenicist's dream is to "improve the genes" -- but "better genes" for what environment?
- The social engineer's dream is to "improve the environment" -- but "better environment" for which genetic natures?