Session two assignment. Research question

Research question: What are some environmental factors that contribute to depression? 

The reason I am interested in this question is because going through my own struggles with depression, I have been told by people of different professions that Norwegians, and other people who live in the far up north; have a higher chance of having mood swings, anger issues, and depression. So as a norwegian I want to know why this is and how I can I prevent this when I have my own children. 

I also hope to understand if my own anger and mood problems is from this ancestral trend.