The levels of analysis in Psychology

Many of you will be studying Psychology for the first time, and will be wondering at the 'levels' of analysis' approach taken by the IB Diploma Psychology course.  This approach, with an acknowledged difference between the biological, cognitive and sociocultural levels of analysing the reasons for behaviour, is also taken by many university courses.  The reason for this goes back to the old and now outdated nature/nurture debate.  How much of our behaviour is inherited and how much is learned? The ...