The biological explanation for the acquisition of phobic disorders establishes that phobias are caused by genetics, innate influences and the principles of biochemistry. This theory recognizes that an oversensitive fear response may be inherited, causing abnormal levels of anxiety. This is illustrated in the basis of inheritance, particularly the adrenergic theory that convicts that those who have an acquisition to phobic disorders consequently show high levels of arousal in the automatic nervous system, which leads to increased amounts of adrenaline, thus causing high levels of anxiety.
However this theory lacks evidence of cause and effect, causing it to be difficult to determine whether the levels of arousal lead to the anxiety or whether it is actually the developed anxiety, which leads to this arousal. This issue was present in Lader and St Matthews study which found that individuals who develop social phobia or panic disorders with agoraphobia have high levels of arousal. This causes a lack of validity to become apparent as there is an unawareness of what is being measured, as there is not a clear distinction between what aroused first, the reaction in the brain or the phobic disorder as it is not convicted whether the high arousal levels are the cause or in fact the consequence of the phobia.
Furthermore, the basis of inheritance also distinguishes that dopamine pathways predispose individuals to be more readily conditioned to acquire phobias, and discerns that abnormally high levels of serotonin activity is a cause of oversensitive fear response also, because it affects areas of the brain included in the fear response, such as the amygdala. This research into serotonin is however inconclusive as, there is an unawareness of whether high levels cause phobic disorders or prevent them as SRI drugs are assigned as medication for those