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.