Abstract
The non-associative, Darwinian theory of fear acquisition proposes that some individuals fail to overcome biologically-relevant fears (e.g. height) because they (1) do not have sufficient safe exposure to the relevant stimuli early in life or (2) are poor habituators who have difficulty "learning not to fear". These two hypotheses were tested in a longitudinal birth cohort study. Study 1 found evidence for reduced exposure to height stimuli in childhood for individuals with a fear of heights compared to study members without fear. Study 2 found evidence for higher levels of stress reactivity (a proxy for habituation) in childhood and adolescence among 18-year-old height phobics compared to study members with dental phobia and those with no fear. The results were discussed in relation to recent findings suggesting that some evolutionary-relevant fears may appear in the absence of traumatic "learning" experiences. The merits of adding a fourth, non-associative pathway to Rachman's [Rachman, S. (1977)] "The conditioning theory of fear acquisition: a critical examination" (Behavior Research and Therapy, 15, 375-387) three pathways model of fear acquisition were briefly considered.