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(唇齿), 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.

Slang(俚语) is very informal language which is often used by young people. It’s hard to keep up to date with it as new words and phrases appear and evolve (发展). Living in a multicultural society has an effect on language, especially on the young, whose friends are often from a mix of backgrounds. TV and music also have a big impact. A complete list of slang is difficult to make; by the time it was finished, the list would be out of date. However, here are a few examples:

Safe, sorted, sound, cool or wicked all mean “That’s good” or “I understand”.

Instead of using different tag questions (附加疑问句) like “… isn’t it?”, “… can’t you?” or “… don’t they?”, people use “innit”.

For example, “He can dance really well, innit!” (= He can dance really well, can’t he?) or “They always say that, innit.” (= They always say that, don’t they?)

Instead of saying “very”, “really” or “completely” use “well”, for example, “I’m well tired” or “You got it well wrong!”

“Whatever” means “I don’t care”, for example, A: “But the teacher says we can’t leave until we’ve finished.” B: “Whatever. I’m going.”

“He’s fine” or “he’s fit” both mean “He’s good-looking”. Fine and fit can describe a boy or a girl.

Not everybody uses slang and not everybody likes it. A school in the north of England recently told its pupils to stop using slang words such as “hiya” (hello), “cheers” and “ta” (both mean “thank you”) if they wanted to get a place at university or a good job.

When British people use language like this, it’s no surprise that some say they can’t understand native speakers. But perhaps learners don’t need to worry so much. Research shows that most of the English spoken around the world today is between non-native speakers of the language.

So, how important is it to understand these slang words and expressions? If you watch films or TV in English, read magazines in English, chat online in English or are interested in English song lyrics, then understanding slang can be very useful. You probably won’t see much slang in your English examination, though.

Ever fought with a problem? Picked up a new skill? Encountered a difficult concept? The language of learning is full of references to parts of the body outside the brain. Perhaps that’s because these phrases suggest something deeper. Researchers are detecting that learning is easier, quicker and more long-lasting if it involves the body.

“In the past, people have argued that as we grow, we become more able to think abstractly (抽象地),” says Andrew Manches, a psychologist at the University of Edinburgh in the UK. Conventional (传统的) thinking might suggest that teachers should help prevent children from using body gestures to prepare them for the adult world. But in truth, the physical world never really leaves our thinking. For example, when we process verbs such as lick, kick and pick, medical scanners show that the parts of our brain that control the muscles in our face, legs and hands, respectively, light up with activity.

Science is beginning to back up the idea that actions really might speak louder than words in the classroom. Spencer Kelly, a psychologist at Colgate University in New York, has found that people spend three times as much time gesturing when they think the message they get across is remarkably important, suggesting that even if only at the subconscious (潜意识的) level, we appreciate the communicative value of our body language. Kelly has also found evidence that a teacher is more appealing to students when he or she uses arm and hand movements to stress points.

Also, some studies indicate that young children obtain more if their teacher uses gestures when explaining a concept. Meanwhile, Sunsan Wagner Cook, a psychologist at the University of Iowa in Iowa City, has found that children pick up new concepts more effectively, if they are taught to mirror and repeat gestures their teacher uses.