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"It seems ... almost as if genes need certain ideal conditions and sufficient time in order to fully express themselves."

Actually the situation, re intelligence as well as other things, is more subtle still. The presumption inherent in "fully express themselves" is that genes code for phenotypic characteristics (such as level of "intelligence") and hence one may only see their "full" effects under some particular set of optimal envrionmental conditions. In practice, genes don't "code for" phenotypic characteristics at all; they "influence" phenotypic characteristics.

Let's imagine two groups of plants with different sets of genes. If we grow the two kinds of plants under identical conditions one grows on the average taller than the other. Hence, genes influence plant height. If we grow either kind of plant under two conditions, one with little light, the other with lots of light, we find that both kinds of plants grow taller with lots of light than they do with little light. Hence, the environment also influences plants height.

Clearly there is no genes versus environment opposition here; both contribute to the height of any given plant under any given condition. More importantly, there is no single way to characterize the relative contribution of genes and environment. Under constant environmental conditions, the variation in plant height is mostly due to genes. But when genes are held constant, the variation in plant height is mostly due to environmental factors. Its not that "genes need "ideal conditions ... to fully express themselves" but rather that the height is always influenced by both genes and environment, with the relative contributions of each being a function of the circumstances in which one makes the observations.

In the case of phenotypic characteristics like intelligence (or other aspects of "mind"), there is a further important subtlety. The naming and measuring of many human characteristics (the creation of stories about them) can itself impact on peoples' stories of themselves and, in turn, influence the expression of those characteristics. For more along these lines in the case of "intelligence," see The Bell Curve: Issues of Individuality and Education. The bottom line, of course, is that there is not only no "optimal" environment for gene expression but also no "optimal" phenotype independent of the environment.