De Boer used computer models to examine the influence of the position of the larynx on the clarity of speech. He did this by using a model of the human vocal tract to measure how many different sounds can be made there. It appeared that the female anatomy is optimally built for making many different speech sounds. The anatomy of apes (with their higher larynx) is considerably worse, and the anatomy of men (with an extra larynx layer) is a little bit worse.
Evolution of speech
An important difference between humans and apes is that the larynx is much higher in monkeys. The larynx is lower in women than in apes, and even lower in men. The theory that the human vocal tract is optimally designed for speech is an old idea, but it has so far been assumed - without proof - that the male vocal tract is best. The research findings of UvA scientist Boyer demonstrating that the female voice channel is optimised for speech, supports the theory that it evolved for speech. He explains that the lower larynx in men helps them sound larger and, therefore, more impressive. Other research suggests that this makes a particular impression on other men.