Introduction

A natural part of our psychobiology, the central motive state of fear is controlled at least in part by hormones. Fear is not uniform. Fear of the unfamiliar, for example, differs from conditioned fear and perhaps from those forms due to innate releasers of fear (Kagan and Schulkin, 1995). Hebb (1946) and others pointed this out some 50 years ago, noting that there is more than one sense of fear, a fact that has biological significance. Hebb emphasized fear of the unfamiliar and fear associated with innate perceptual sensibility. Both humans and chimpanzees (Pan troglodytes), for instance, are afraid of headless animals. This chapter will explain how humoral signals – specifically glucocorticoids and corticotropin-releasing hormone (CRH) – help to sustain some fear-like states.

Many thinkers in this century have construed fear either as an intervening variable (e.g., Miller, 1959–71; Davis et al., 1993) or as a tool with which to predict behavior, “but nothing inside in which to frame a science” (e.g., Skinner, 1938). That is not my view. Fear is a property of the nervous system, as well as a product of our evolutionary history.

Although emotions are often construed as passive (e.g., by Spinoza and Freud) (Parrott and Schulkin, 1993), fear is an active response, rather than a passive response. As a product of our evolution, fear generates adaptive, problem-solving behaviors. When emotions such as fear are placed in this functional light, they come closer to what Charles Darwin (1965), William James (1952), and John Dewey (1894, 1895), had in mind – that fear is a biological phenomenon linked to the perception of danger and the behavioral reactions to avoid it.