ABSTRACT
The idea that individual differences in temperamental qualities are subserved by stable biological characteristics has a long history. Most observers within the past century who have written on the subject of temperament have speculated that such individual differences are "biologically based" (e.g., Thomas & Chess, 1977). Unfortunately, the ascription of a biological basis to a trait adds little to its understanding for several reasons. First, it is unclear whether a heritable cause is implied when a biological basis is proposed. Second, from a psychobiological perspective, any difference in behavior must be biologically based because the brain is the organ that underlies behavioral operations. In this sense, temperamental differences are no different from any other trait-like difference among people. So, we must ask the question whether temperamental characteristics enjoy any special status among traits with respect to their underlying biological substrates. I believe the answer to this question must be affirmative. At least some temperamental characteristics refer to differences among individuals in basic or elemental processes such as propensity to approach or withdraw in the face of novelty. Such differences in basic biobehavioral processes are more likely to have direct links with underlying biological processes than more complex traits such as obedience to authority or religious values. While such differences must also be biologically based in the trivial sense (i.e., the proximal cause of any behavior must be a particular underlying pattern of biological events), they are likely to depend upon an incredibly complex pattern of biological activity in many different systems.
