Parental history, aversive exposure and the development of snake and spider phobia in women.

Parental history and experiential factors in the development of snake and spider phobia were studied. Phobic women (DSM-IV, n = 158) reported on family history of animal phobia and whether direct (being frightened by the phobic object) or indirect (seeing someone else being frightened by and/or being warned of the phobic object) fear exposure predated phobia development. Fifty-nine mothers (37%) and 11 fathers (7%) had snake or spider phobia, which is higher than the upper 95% confidence interval in the populations (Fredrikson, Annas, Fischer & Wik, Behavior Research and Therapy, 34, 33-39). Lifetime Relative Risk, RR, of animal phobia in probands' mother and fathers as a function of at least one phobic grandparent was 3.3 and 13.7 respectively. Indirect fear exposures were more common in snake (45%) than spider (27%) phobics (RR = 1.4). Indirect fear exposures were more common among probands with a positive parental history, the RRs being 3.6 and 2.1 as a function of maternal and paternal family history. Direct exposures were unrelated to parental history. The familial resemblance and transmission of specific phobia could be experiential in origin mediated by indirect exposures or of hereditary origin mediated by genetic factors. It may represent genetically facilitated learning and exemplify imprinting in humans.