Instead of looking at types of sounds as the source of human speech, we can look at
the types of physical features humans possess, especially those that are distinct from
other creatures, which may have been able to support speech production.We can start
with the observation that, at some early stage, our ancestors made a very significant
transition to an upright posture, with bi-pedal (on two feet) locomotion, and a revised
role for the front limbs.
Some effects of this type of change can be seen in physical differences between the
skull of a gorilla and that of a Neanderthal man from around 60,000 years ago. The
reconstructed vocal tract of a Neanderthal suggests that some consonant-like sound
distinctions would have been possible. We have to wait until about 35,000 years ago
for features in reconstructions of fossilized skeletal structures that begin to resemble
those of modern humans. In the study of evolutionary development, there are certain
physical features, best thought of as partial adaptations, which appear to be relevant
for speech. They are streamlined versions of features found in other primates. By
themselves, such features wouldn’t guarantee speech, but they are good clues that a
creature with such features probably has the capacity for speech.