2. Laughter improves social relationships

3. Humans can hear the difference between involuntary and voluntary laughter.

4. Laughter may have emerged as the size of social groups increased.

5. Voluntary laughter uses the positive effects of involuntary laughter.

6. Humans can distinguish between laughter among friends and among strangers.

7. Dolphins also have a form of laughter.

8. Adults are better than children at distinguishing between types of laughter.

1. Chimpanzee laughter sounds very similar to human laughter.

2. 2. Scientists believe that laughter used to be a threatening signal.

3. Humans were probably laughing before they were speaking.

4.Tickling results in voluntary laughter.

5.Women can better distinguish between the two types of laughter than men.

6.The brain responds differently to voluntary and involuntary laughter.

7. 7. Children are not as good as adults at distinguishing between the two types of

8. Hunter-gatherers are better than most people at distinguishing between types of laughter.