The bio-evolutionary perspective presents one aspect of the nature versus nurture explanation for nonverbal behavior. It considers why various behaviors contribute to survival or procreation and what physiological features correlate with those behaviors. The biological and physiological explanations for behavior complement, rather than compete with, social and cultural ones. The evolutionary aspect includes the theory of natural selection and those features that are inherited. Two key elements are (1) that a trait or tendency be at least partially genetic and (2) that it enhanced the likelihood of survival and/or procreation. The bio-evolutionary perspective relates to nonverbal communication in affiliation, attachment, bonding, dominance, and sexuality. The physiological aspect includes changes in body chemistry, such as releases of dopamine and cortisol, which influence behavior. All human cognitive, emotional, behavioral, and social events have associated physiology. This is illustrated through the relation of physiology to emotions.