ike any other large scale and public human endeavor, the process of medical research is influenced by prevailing ideas and cultural currents. Medical research into the causes and origins of bipolar illness has been influenced by a prevailing idea known as the Diathesis-Stress Hypothesis which has been applied to many medical disorders. The basic diathesis-stress hypothesis proposes that people have predispositions and vulnerabilities for illnesses (known as diatheses). Some people have more of these susceptibilities than others, for varying reasons having to do with their genetics, biology and experience. Merely possessing a vulnerability for an illness alone is not enough to trigger that illness into action, however. Instead, people's vulnerabilities must interact with life stresses to prompt the onset of the illness. The greater a person's inherent propensity for developing an illness, the less stress is necessary to get the illness started. Conversely, where there is a smaller susceptibility for developing an illness, a greater amount of stress is required to produce the illness. Until this critical amount of stress is reached (however much or little of it is necessary in a given case) people cannot be said to have an illness, and their vulnerabilities are said to be "latent" (hidden).