Based on an interest of human behaviour derived from ancestors, it is safe to say that your field of interest is human evolution and/or anthropology.
Human evolution is largely focus on the concept of Darwinism, (Charles Darwin's philosophy), which is, in summary, a survival of the fittest notion. It explains how all living species evolve by inheriting characteristics that constantly vary and change in order to improve and succeed the race. If this is not done, the species will die out and thus it is unable to pass on it's 'bad' genes, so it suffices to say that evolution is based on a constant process of gene 'improvement', or at least relative adaptation to survival.
Anthropology is in essence, the study of humans. It covers studies related to their past, their present, their ancestors, society and biology.
I hope this answers your question.