To look at the biological perspective of the causes of depression the most logical and obvious way in which to do this is to look into genetics.  Seeing as how genetics are what decide whether or not we are male or female, have blue or brown eyes and even if we are going to loose our hair as we age.  It only makes sense to look at ones genes to see if they are more or less likely to suffer from depression because of those same genes. 

    In the text "Psychology: Themes and Variations, Briefer Edition" (Weiten, 2008) it simply state that genetic factors are strongly suggested to influence the likelihood that one will develop a major depression disorder.

    In the article "Genetic Factors of Depression and Suicide" (Rainer, 1984) it goes on to to state that the amount of evidence to there being a genetic component to major depression illnessess is growing larger and larger.  It also states that a first degree relative of a person with a bipolar disorder is over twenty times as likely to be affected with a bipolar or a unipolar disorder.  Now if the relative has a unipolar disorder the likelihood of a relative being affected are ten to fifteen times higher than that of the general public.

    In "DNA's Moody Temperment" (Bower, 2005) it states that scientists for the first time have seen what a genetic predispostion looks like using magnetic resonance images of the brain and that these images show that people who have poor control of their neural reasctions to stress and threats have inherited a particular short version of a particle gene.  What causes the problem is this gene, bu having intense serotonon activity, degrades the connection to the brains mood regulation center.