Genes and environment. One we can control, one we cannot.
Now it appears we may have less control over the environment factor than most of us assume. According to an article printed by Reuters yesterday early family life may have the ability to counter a 'depression gene.'
What's the depression gene? Per the article people who carry a short version of the serotonin transporter gene (5-HTTLPR) appear more susceptible to depression than those lacking the variant.
Interestingly, researchers claim that those people with the short version of the gene who grow up in lower stress environments were less likely to exhibit signs of depression.
In your eye nature. Score one for nurture. If only it were easier to control your environment as a child...
I'll leave it to you to look deeper into the study's methodology.