That may be a hint that yawn evolved as a social cue—"time for us all to go to bed".
也许这是打哈欠进化为社交线索的一种暗示——“到我们大家睡觉的时间了”。
2
Every time you feel the cue for a snack, insert another routine.
每当你想吃点东西的时候，就去干点别的事情。
3
That may be a hint that the action evolved as a social cue - "time for us all to go to bed" - although as usual when evolution and human behaviour meet, the tie is speculative at best.