There's reason to believe that the combined effect from all these different gene variants is approximately linear. Effects caused by multiple variants interacti

There's reason to believe that the combined effect from all these different gene variants is approximately linear. Effects caused by multiple variants interacting are difficult for natural selection to operate on because of the way sexual reproduction works. See section 3.1 of this paper, "On the genetic architecture of intelligence and other quantitative traits": https://arxiv.org/abs/1408.3421 https://arxiv.org/abs/1408.3421