In the service of illustrating what seems to be individual differences in plasticity, and thus, differential susceptibility in existing G × E research, we adopt a liberal standard of evidence once a significant crossover interaction has been detected when it comes to regarding the results as evidence of differential susceptibility to environmental influences. Specifically, and with regard to subgroup means, if one subgroup shows both the highest and the lowest mean of all susceptibility-factor-defined subgroups (for example, short vs long 5-HTTLPR allele) on an outcome with regard to the environmental effect in question, this is interpreted as in line with the for-better-and-for-worse differential-susceptibility patterning of results. Similarly, but with regard to slopes, whenever they indicate that one subgroup defined on the basis of the susceptibility factor in question would score highest and lowest given the environmental influence under investigation (that is, steepest slope), this too is interpreted as evidence of differential susceptibility. All the findings to be presented meet these criteria, with some pertaining to MAOA, some to 5-HTTPLR and some to DRD4.
