HUMAN NATURE: Interaction of genes and environment

In only a very few cases is it fair to say that a trait is due almost entirely to nature, or almost entirely to nurture. [citation needed] In the case of most diseases now strictly identified as genetic, such as Huntington's disease, there is a better than 99.9% correlation between having the identified gene and the disease and a similar correlation for not having either. On the other hand, such traits as one's native language are entirely environmentally determined: linguists have found that any child (if capable of learning a language at all) can learn any human language with equal facility. With virtually all psychological traits however, there is an intermediate mix of nature and nurture, and opinions about the relative importance of each will often vary widely.

Examples of environmental, interactional, and genetic traits are:
Predominantly Environmental Interactional Predominantly Genetic
Specific Language Height Blood type
Specific Religion Weight Eye color
Skin color
The "two buckets" view of heritability.
The "two buckets" view of heritability.
More realistic "homogenous mudpie" view of heritability.
More realistic "homogenous mudpie" view of heritability.

Steven Pinker (2004) likewise described several examples:

concrete behavioral traits that patently depend on content provided by the home or culture—which language one speaks, which religion one practices, which political party one supports—are not heritable at all. But traits that reflect the underlying talents and temperaments—how proficient with language a person is, how religious, how liberal or conservative—are partially heritable.

When traits are determined by a complex interaction of genotype and environment it is possible to measure the heritability of a trait within a population. However, many non-scientists who encounter a report of a trait having a certain percentage heritability, imagine non-interactional, additive contributions of genes and environment to the trait. As an analogy, some laypeople may think of the degree of a trait being made up of two "buckets", genes and environment, each able to hold a certain capacity of the trait. But even for intermediate heritabilities, a trait is always shaped by both genetic dispositions and the environments in which people develop, merely with greater and lesser plasticities associated with these heritability measures.