I don't know if this is old news to you guys, but I found this explanation for depression quite convicing. Here's a lecture given by Professor Sapolsky, at Stamford University, on the evidence of genetic predisposition to depression. He's very clear and easy to understand. Last 5 min of Lecture by famed professor at Stanford University, Robert Sapolsky on Depression and Genetics. Scientists have identified the Gene responsible for depression by studying thousands of children for 20 years. http://www.youtube.com/watch?v=E3YP5HJU-q4 I love how he talks and how he explains things. Professor Sapolsky states: "There's nothing out there like Depression. Depression is absolutely crippling. Depression is incredibly pervasive.... Basically depression is like the worst disease you can get....It is devasting. It is wildly common....15% of us will get it at some point in our lifetimes. Currently, World Health Organization says that depression is the 4th leading cause of disability around the world." The theory states that people with this particular mutation in the brain, respond much more severely to stress than people without the mutation. And that with each occurrence of a stressful even the likelihood of depression grows significantly. People with the mutation (something about a short alele) are about 33% more likely to develop depression. In other words, the combination of the genetic mutation AND stress, is what trigger the depression. Now I realize that there are whole bunch of articles on the web saying that the Depression Gene theory has been disproven, but I can't help but think that it really makes sense. Especially given the evidence in my life.