More than 30 years ago, the scholar Charles Hockett noted that speech

sounds called labiodentals, such as “f” and “v”, were more common in the

languages of societies that ate softer foods. Now a team of researchers led by

Damián Blasi at the University of Zurich, Switzerland, has found how and

why this trend arose.

They discovered that the upper and lower front teeth of ancient human

adults were aligned (对齐), making it hard to produce labiodentals, which

are formed by touching the lower lip to the upper teeth. Later, our jaws

changed to an overbite structure (结构), making it easier to produce such

sounds.

The team showed that this change in bite was connected with the

development of agriculture in the Neolithic period. Food became easier to

chew at this point. The jawbone didn’t have to do as much work and so

didn’t grow to be so large.

Analyses of a language database also confirmed that there was a global

change in the sound of world languages after the Neolithic age, with the use

of “f” and “v” increasing remarkably during the last few thousand years.

These sounds are still not found in the languages of many hunter-gatherer

people today.

This research overturns the popular view that all human speech sounds

were present when human beings evolved around 300,000 years ago. “The

set of speech sounds we use has not necessarily remained stable since the

appearance of human beings, but rather the huge variety of speech sounds

that we find today is the product of a complex interplay of things like

biological change and cultural evolution,” said Steven Moran, a member of

the research team.

32. Which aspect of the human speech sound does Damián Blasi’s research

focus on?

A. Its variety.

B. Its distribution.

D. Its development.

C. Its quantity.

33. Why was it difficult for ancient human adults to produce labiodentals?

A. They had fewer upper teeth than lower teeth.

B. They could not open and close their lips easily.

C. Their jaws were not conveniently structured.

D. Their lower front teeth were not large enough.

34. What is paragraph 5 mainly about?

A. Supporting evidence for the research results.

B. Potential application of the research findings.