The same factor may produce opposite effects in different individuals. For instance, parental substance abuse as an environmental factor may both promote similar behavior in offspring (by providing a ready access to alcohol and other drugs) and produce aversion to it (by demonstrating clearly the negative effects). The vectors may interact; e.g., the role of genetic factors may be contingent on environmental ones, and vice versa, as, for instance, was shown for heritability of disinhibition (a scale evaluating the need to disinhibit behavior in the social sphere by drinking, partying and seeking variety in sexual partners), which depended on receiving a religious upbringing (Boomsma et al., 1999). Particular genes or environmental factors may be of special importance for an individual trajectory regardless of heritability, and an individual trajectory may have little to do with the forces detectable at the population level (an example of the strong association between a rare mutation in the MAOA gene and aggressive behavior (Brunner et al., 1993) illustrates this point). The sets of vectors may also undergo secular changes and vary across different populations.
