The human larynx or “voice box” (containing the vocal folds or vocal cords) differs
significantly in position from the larynx of other primates such as monkeys. In the
course of human physical development, the assumption of an upright posture moved
the head more directly above the spinal column and the larynx dropped to a lower
position. This created a longer cavity called the pharynx, above the vocal folds,
which acts as a resonator for increased range and clarity of the sounds produced via
the larynx and the vocal tract. Other primates have almost no pharynx. One unfortunate
consequence of this development is that the lower position of the human larynx
makes it much more possible for the human to choke on pieces of food. Monkeys
may not be able to use their larynx to produce speech sounds, but they do not suffer
from the problem of getting food stuck in their windpipe. In evolutionary terms, there
must have been a big advantage in getting this extra vocal power (i.e. a larger range
of sounds) to outweigh the potential disadvantage from an increased risk of choking
to death.