Why women speak better than men (and its significance for evolution)

In order to make distinctive speech sounds, it is necessary to control two separate
acoustic cavities. There has been a longstanding debate about whether a lowered larynx is
essential for this. Lieberman and Crelin have used it as an argument against speech in
Neanderthals. This claim is controversial, not only for paleontological reasons, but also
because researchers do not agree on the need of a lowered larynx for distinctive speech.
Researchers using similar methods (computer modeling) arrive at opposite conclusions.
The problem is that one needs to take articulatory and anatomical constraints into account
when investigating the acoustic implications of vocal tract morphology.
In order to study what the effect of lowering the larynx is, a reimplementation of
Mermelstein’s vocal tract model has been made. This is a computer model of the
geometry of the (human male) vocal tract, whose controls correspond to the actions of the
muscles involved in speech. This model was used to explore the possible articulations
and the corresponding acoustic signals of different vocal tract geometries.
Experiments were run with the original male model, a model of the female vocal
tract and a model that is a combination of these two tracts. It was also found that the
female vocal tract is better than the male one. This observation was confirmed by a
reanalysis of the data from the Peterson and Barney study. This establishes an
evolutionary advantage of a vocal tract that has a pharyngeal and oral cavity of equal
length (as in the female tract). It has a larger signaling space than the male tract. Males
probably had evolutionary advantage from size exaggeration, as proposed by Fitch. It
must be noted however, that the differences found so far are significant but small.