This means that a social smile has Darwinian value.

这个表明社交式微笑符合达尔文进化论价值。

youdao

It's around this time that babies develop a real social smile in response to another smiling person.

大概在这个时候，宝宝们才会开始对其它微笑的人展现微笑。

youdao

Then she started, a little social smile came on her face, for a moment she looked the pleasant hostess.

然后她又睁开眼，脸上露出上流社会人物的微笑，一时间她很象一位愉快的女主人了。

youdao

By contrast, a standard social smile, which is sometimes called a Pan Am smile after the polite expression the former airline's stewardesses used to greet passengers, activates only the muscles around the mouth.

WSJ: Stress-Busting Smiles