may accentuate and reinforce the personality characteristics that were partially responsible for the particular environmental elicitations in the first place”. This principle illustrates how gene-environment interactions maintain and reinforce personality throughout the lifespan. Three main types of gene-environment interactions are active (the process by which individuals with certain genotypes select and create environments that facilitate the expression of those genotypes), passive (the process by which genetic parents provide both the genes and the early environmental influences that contribute to the development of a characteristic in their children), and reactive (the process by which non-family individuals respond to the behavior produced by a genotype in characteristic ways). An example of the way environment can moderate the expression of a gene is the finding by Heath, Eaves, and Martin (1998) that marriage was a protective factor against depression in identical twins, such that the heritability of depression was as low as 29% in a married twin and as high as 51% in an unmarried twin. Stability of personality Over the course of an individual's lifespan, the stability of their personality has been shown to be variable, although this variability levels out in adulthood. Behavioral genetics can account for the variability experienced across the lifespan. This is highly evident in the transitions between childhood, adolescence, and adulthood. From childhood to mid-adolescence, the rate of individual differences in personality increases, primarily due to environmental influences. However, genetic influences play a larger role than environmental influences in adulthood, resulting in fewer individual differences in personality between individuals who share similar genetics. The stability of personality across one's lifespan is further evidenced by a longitudinal study conducted on individuals across the span of fifty years from adolescence through adulthood. The results of this longitudinal study suggested that the personality was malleable, although variations in the level of malleability stabilized in adulthood. A study published in the Journal of Personality and Social Psychology examined personality developing in college students based on the Big Five personality trait domains and facets within those domains. The results suggested that the rank-order stabilities of facets were high, with values greater than .50 (indicating a strong correlation); the results for trait domains were similar to individual facets. High rank-order stability is further evidenced by another study that integrated personality structure, process, and development. This study included previous research that indicated high-order rank stability; it also included research that indicated variation in this