Human speech contains more than 2,000 different sounds, from the common “m” and “a” to the rare clicks of some southern African languages. But why are certain sounds more common than others? A ground-breaking, five-year study shows that diet-related changes in human bite led to new speech sounds that are now found in half the world’s languages.

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.

1.Which aspect of the human speech sound does Damián Blasi’s research focus on?

A Its variety.

B Its distribution.

C Its quantity.

D Its development.

解析：选D。D 细节理解题。根据文章第一段中的“Now a team of researchers...has found how and why this trend arose.”可知Damian Blasi的研究重点是在语言的演变上。故选D。

2.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.

解析：选C。C 细节理解题。根据第三段中的“They discovered that the upper and lower front teeth of ancient human adults were aligned, making it hard to produce labiodentals...Later, our jaws changed to an overbite structure, making it easier to produce such sounds. (他们发现，古人类的上门牙和下门牙是对齐的，因此很难产生唇齿音，唇齿音是通过下唇接触上牙齿而形成的。后来，我们的下颚变成了覆盖咬合结构，更容易发出这样的声音。)”可知，因为古代成年人的下颚结构使他们很难发出唇齿音。故选C。

3.What is paragraph 5 mainly about?

A Supporting evidence for the research results.

B Potential application of the research findings.

C A further explanation of the research methods.

D A reasonable doubt about the research process.

解析：选A。A 段落大意题。根据第五段中的“Analyses of a language database also confirmed that... (对语言数据库的分析也证实，在新石器时代之后，世界语言的发音发生了全球性的变化，在过去几千年里，“f”和“v”的使用显著增加。这些声音在今天许多狩猎采集者的语言中仍然没有发现。)”可知，第五段主要是通过列明数据分析结果来进一步证明研究结果。故选A。

4.What does Steven Moran say about the set of human speech sounds?

A It is key to effective communication.

B It contributes much to cultural diversity.

C It is a complex and dynamic system.

D It drives the evolution of human beings.

解析：选C。C 推理判断题。根据文章最后一段中“‘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.(研究小组成员Steven Moran说：“自从人类出现以来，我们使用的语音不一定保持稳定，我们今天发现的各种语音都是生物变化和文化进化等复杂相互作用的产物。”)”可知，Steven Moran认为语音是一个复杂的动态系统。故选C。