Chicken And Egg Scenario

The chicken and egg scenario is a thought problem that is also used to describe many real life situations. What came first - the chicken or the egg? Chickens are hatched from eggs so the egg must have appeared first. But eggs come from chickens so the chicken must have appeared first. See the quandary? This is a cyclical thought problem that illustrates how a perpetual loop works.

A real life example of how this is metaphorically used in psychology is depression. Some people with depression have been shown to have brain differences such as shrinkage. Do these brain differences cause depression or does depression cause these differences? Another example is that psychopaths have a high incidence of frontal lobe abnormalities. Do these abnormalities cause psychopathy to develop or does the psychopathic personality cause these changes?