thumbelina said:Or do they just become that way over the course of their lives?
Well, if we look at the most obvious example; would a certain Hitler have been Hitler regardless of the life he lived? 🙂
I suppose personality formation really boils down to two main factors: phenotype and genotype.
In this context, phenotype represents the influence of one's environment, whereas genotype refers to what is essentially "innate."
If an individual grows up in a toxic environment—dealing with constant harassment from a young age, chronic stress, and things of that nature—there is a significant chance they will develop into a similarly troubled person. I suspect that almost any mental disorder can trace its roots back to childhood. This is why psychoanalysis is conducted in such a way, using regression to help the patient revisit those early experiences that shaped their subsequent development.
As for the genotype, psychology suggests the existence of a "collective unconscious" where atavistic experiences are stored (for instance, a certain reverence for God, even in people who haven't had much exposure to holy books or religious laws). One often notices a child exhibiting identical behavioral patterns to their parents, even if they don't live together—specifically in their gestures, facial expressions, or similar reactions to various stimuli.
Furthermore, one might find certain basic models in psychology (though they aren't strictly established scientific facts) based on physical facial features.
For example, a strong, prominent chin might suggest a strong character.
Thin lips might indicate someone who is somewhat cowardly... though, of course, none of this is necessarily a hundred percent accurate.
I would argue that facial expressions and movement say far more about a person's character than their static physical traits.