All of this operates through cause and effect or karma, acted on by intelligence, will, and emotion. Among human beings the changes made in ourselves are for the most part interior, in the realm of talent and character. They are unseen, although these inner changes may reflect themselves physically in time, if not in this life, then in subsequent lives. Other explanations might be devised to explain the same facts, and so long as they cover all the facts they would have validity. Of course if additional facts are discovered that contradict certain theories, scientific or metaphysical, then those theories would have to be modified.
Theosophists also place a great deal of importance upon the germ plasm.
It is indeed the sole physical transmission from parent to child. This may explain why the Greeks, for example, included what they called palingenesis among their explanations of reimbodying souls. When human death occurs, there is a withdrawal of the consciousness. After the earthly elements are dropped, the higher portion of the soul rests in a dream world, absorbing and bringing to fruition the unfulfilled aspirations and thoughts of the previous life. All is incorporated into the nature, so that in the next life the soul will return amended and enlarged in proportion to the inner forces that governed the last life or incarnation.