Genes are the only heritable component of this hairball. And therefore dictate to the maximum extent possible the result. Genes that are able to exert better control over the hairball will yield higher IQs.

Also technically there is only the environment, once the genes are instantiated they become part of the environment too. The digital information of heritability is the only thing that can exert systematic control.

We use linear methods to establish heritability. While the actual process is most decidedly nonlinear and subject to chaos.