Depression can be as much as 40% genetic and the rest is environmental in nature. Although it existed in paleolithic times, the way it manifested and how our ancestors dealt with it it must have been much more different from how we experience it today. 
Depression became a separate illness in the twentieth century, and by the 1980's it became an epidemic that just keeps growing into this century. What is happening? Why are our children and young adults affected the most?
Let's look for answers.