Biological basis of personality
Personality is not a neat science. From the beginning there has been fuzzy boundaries on the definition of all the factors involved in personality assessment. With the major assessment tool being the five factor model being derived from a "lexicographer's nightmare," early in the 20th century, it is not surprising that a great deal of effort has been invested in clarifying structures amenable to research.
Zuckerman (1993) has given the field a framework for sorting out the mess. In a rather cute metaphor, he has likened the structure of personality research to seven turtles standing on each other's backs (see figure 1.) Personality can be viewed from multiple perspectives. Additionally, if a lower turtle moves, the turtles above will be effected. However, since they all have hard shells, each can be seen as completely independent. So, while a change originating in the study of the genetics of behavior will have important implication on trait theory, trait theory can continue relatively oblivious to the latest findings in genetics, neurology, biochemistry, etc.
In this paper I will look at the lowest level of analysis. Genetic research in personality can be divided into two major field of research. The first has a long history, and the second is new and exciting. The first is called quantitative genetics, and the second is molecular genetics. Quantitative genetics uses statistical analysis of phenotypes across specific populations to arrive at estimates of the hereditability of personality traits. As we shall se there are a number of well-developed tools for evaluating genetic influence on personality using this paradigm. Also, we shall note a few deficiencies in this way of evaluating hereditability.
The second method is molecular genetics. As late as 1982 Cattell said, "one would doubtless like to know how many genes account for...