This seems to be the nature/nurture question. I think it is rather idiotic to believe that the brain is not inherently genetically determined as other biological characteristics that are visible. So nature is the, inalterable, start and factor determining how nuture will affect the person. In all of nature, with the exception of zebra's I guess, there are no two identical things so, no matter the nuture were it possible for that to be identical, no two people will ever be alike... including MBTI types.