The nature vs nurture complex has been debated for an undecidedly long time. I'm no psychology expert but I believe the idea is to question whether traits such as personality and lifestyle are created at birth, or developed over time by upbringing and environment, nurture.
Doctor Who would suggest that a person is born with a body and personality, rather than materialized from a lifetime. Each regeneration is a new birth, a new body. He also comes with a brand new spanking personality, though his past never changes. His memories, knowledge and experiences never change, but never affect his personality.
I wish I could say this is proof but it is unfortunately a mere observation.
Who was your favourite Doctor? And do you wish you could regenerate?