and is stable across time. Although we take seriously previous failures to “pin down” measurable nonshared environmental experiences, our findings suggest a substantial amount of variance exists in personality traits that is truly environmentally mediated, not random error of measurement, and unrelated to state-like fluctuations. This result should be considered an encouraging prospect for future investigation of measurable environments. Longitudinal, genetically informative samples will likely be necessary to pin point the specific enduring environments and locations in development during which the environment exerts a causal effect. Whether such measurable environments can be realistically expected to explain the totality of stable nonshared environmental effects is, however, unclear.
