These are all determined by hormones produced by the body, mostly starting at puberty. If, for some reason, the hormone production does not match the primary genderic signs, the secondary ones may not match.

All of the ones for males are determined by the presence of testosterone in the blood. Lack of this hormone will cause them to not occur. The ones usually associated with females are not completely caused by estrogen, however, as some of them may be considered to be "defaults". For example, the male voice is deeper due to the growth of the voicebox. Others are, such as breast growth, and the softer, rounder features.