When I speak to the people about soul, and how it incarnates
in new body, people ask me how it is possible, that this soul
(since I say that it is not material) get hereditary characteristics
of parents?
One of their examples is that the father of the person was
strong heavy man warrior who never cried in his life, and the
mother of the person was very emotional women. The person
became very strong and brave on one side, but very emotional
as well (whenever there is some movie with sad scene, he is
often the only one crying in the full room of people).
Their only conclusion is that he became such a person by the
combination of the characteristics of the parents that made him
as he is now, otherwise why would some soul accept to have some
characteristics of some parents that he does not agree to have,
or are strange to him, or so.
So they ask how is that?, and that their only explanation is that
there is no soul, since if it exists it would have only its own
characteristics brought from previous existence, and it may
get some new in this life by education and new experiences
in this new life.
How to answer this question?
How does the soul, which is not matter, acquire material characteristics?
Through identification.
The soul cannot exist without identifying with something. There are two basic choices of what to identify with: matter or consciousness. Souls in the world identify with matter in the form of the mind. Guru Maharaja says in his commentary to Gita 2.14: "All of these experiences are relative to the mind's marriage to the senses and their perception of sense objects. . . . These mental perceptions create a world in which the self lives without knowledge of itself, the world of the mind." The soul identified with matter loses the ability to distinguish itself from matter, and is thus lost in the world of the mind.
To answer the objection that the soul would not accept the characteristics of parents she did not agree to have, the explanation is karma. Our actions, set in motion by our samskaras (see below), create reactions. The soul gets parents according to her karma, and takes on their characteristics through association, not by choice. It's well known that we become like those we associate with, so no big mystery there. We must also remember that the soul herself is not the doer in a direct sense (as we see in the Gita) and remains aloof from the movements of prakrti, even while totally enmeshed in the web of karma.
A note about samskaras: when we experience something, an impression is formed in the mind. The more we experience something the deeper the samskara becomes. Samskaras are stored in the mind (the manomaya-kosha, or "mental sheath" to use yogic terminology) and since the jivatma carries the mind with her throughout all her incarnations the samskaras from previous births go with her also. Samskaras manifest as tendencies and dispositions for some things and against others, and when these tendencies mix with what we learn from our parents our personality in a given lifetime is formed.