Sometimes a theory gains credence purely by observing the behaviour of people on this forum.
Whilst researching re-incarnation, I came across a theory that many of today's human population had their last incarnation as animals, and their subconcious minds still operate at the level of
herd or
predator 
Judging by the tone of many posts here, that might well be true.
There is no way of proving it, so it will remain a 'theory' - it just seems to explain a lot.