The research carried out in the field of behavioural genetics has indicated, over the course of many studies, that genetic influence has a direct affect on individual differences in personality. Still, behavioural genetics has a lot to provide to the study of personality than inheritability predicts. This paper will discuss a few of the findings from research carried out on behavioural genetics in personality that go beyond the basic question; nature vs. nurture. The findings from the research include genetic continuity and environmental change during development, the impact of shared and non-shared environmental influences on personality and personality as a go-between of genetic influence on environmental measures. There are two general methods that have commonly been employed by behavioural geneticists investigating the genetic influence on personality: twin studies and adoption studies.
Recently, there has been a surplus of behavioural genetic studies in the aetiology, particularly when discussing individual differences in personality. The results conclude that ‘Most personality traits show some genetic influence’; this has now become accepted within the study personality, (Plomin, & DeFries, 1996). A very important discovery in genetic research on personality relates to the environment. It has been stated that genetic aspects are responsible for approximately 20 to 50% of the phenotypic variation in personality. The remaining variation is said to be the cause of environmental aspects. On the other hand, the study of twins and adoption find that shared family environments are accountable for only a small portion of variation in a majority of element of personality (Plomin, & DeFries, 1996).
It is important to note that there are a few aspects of this study that have grown to be quite complex. One of these aspects is the theory and research stating the differences between environmental influences on personality. First of all, a majority of researchers focus on comparing how shared and non-shared environmental aspects influence personality. Eysenck (1991) suggested that siblings or twins who shared environmental influences contribute only slightly to personality differences. Though an interesting point surfaced as a result of studies carried out by Plomin et al (1992); environmental aspects, unique (non-share) to family members, are influential over shared environmental aspects. Family personality is similar primarily due to the DNA which is shared with one another and not because of the shared family environments. This was established in a study of infants personality where a correlation was found for temperament to be about .00 for genetically unrelated adoptive siblings—which provides a direct test of shared family environment—and .20 for genetically related non-adoptive siblings (Braungart, Plomin, DeFries, & Fulker, 1992).
A question can be posed based on these results, if shared family environments do not shape personality, then what does? The answer lies within families and not between families. “The environmental influences that are important to personality are those aspects that are not shared by members of the same family—that is, environmental influences that are unique to family members” (Pedersen et al., 1992). These environmental influences (non-shared) make family members different from each another (Plomin & Daniels, 1987). Non-shared environmental aspects could include differential parental treatment; differential extra familial relationships with friends, peers, and teachers; and non-systematic aspects such as accidents or illness (Plomin, Chipuer, & Neiderhiser, 1994). The examination of environmental aspects that differ across families is not as beneficial to this study as the examination on environmental factors that differ within families. However, Reiss (1997) and Harris...