Evidence FOR Genetic Explanations
Fyer et al (1990) 31% of close relatives of phobics also had a phobia.
Ost (1989) 64% of blood phobics have at least 1 relative who is also blood phobic.
Kendler & Karkowski (1999) 1708 female twins were studied. They found that heritability was high for blood-injury phobia, animal phobia and situational phobia.
Fyer et al (1993) 16% of close relatives of social phobics develop social phobia. Only 5% of the relatives without social phobia developed social phobia.
Kendler et al (1999) Genetic factors are underestimated due to poor reliability of diagnosis of phobias. Genetic factors are moderately important.
Evidence FOR Genetic Explanations (continued)
Torgersen (1983) 31% concordance rate in identical twins and 0% in fraternal twins (small sample size).
Harris et al (1983) Close relatives of agoraphobics are likely to suffer from an anxiety disorder (when compared to a non-phobic).
Crowe et al (1986) 12% of agoraphobics have close relatives with agoraphobia. 17% had a phobic disorder. Much higher than normal.
Bienvenu et al (2007) studied 7800 twins. They found strong genetic links between social phobia, introversion and neuroticism. Same for agoraphobia BUT NOT specific phobia.
Evidence AGAINST Genetic Explanations
Fyer & Ost Findings can be explained as social learning theory.
Eysenck Genetic factors are moderately important in specific phobia.
Skre et al (1993) Found that concordance of social phobia was the same between fraternal twins and identical twins. This suggests that the phobia was probably caused environmentally- or at least a social trigger.
Torgersen's 1983 study contained a small sample size.
Genetic factors affecting social and agoraphobia may be different from those for specific phobia.
Kendler (1995) Genetic vulnerability is general. If you have a twin with social phobia, you may end up with social phobia, agoraphobia or anxiety disorder.