Dr. Marina Davila-Ross and her research team from the University of Portsmouth in England, United Kingdom analyzed almost 500 videotaped play sessions of 59 chimpanzees living in four groups in the Chimfunshi Wildlife
Orphanage of Zambia.

They found that these friendly chimps would join the laughter of their playmates, even though they may not think the situation to be that funny. Such responsive laughter was shorter than spontaneous laughter.

It occurred more often in newer groups rather than those that had been established for a longer period of time. This suggested its important role in promoting social interaction. It was also thought to be similar to conversational laughter of humans.

Our thankfulness, Dr. Davila-Ross and colleagues, for highlighting the amicable nature of beautiful chimpanzees. May these gracious co-inhabitants be protected to live in joy and laughter for eons to come.
http://www.dailymail.co.uk/sciencetech/article-1362051/How-chimpanzees-just-like-humans-They-
laugh-jokes-bond-funny.html#ixzz1FRtGjd2w http://chimpanzeeinformation.blogspot.com/2011/03/chimpanzees-laugh-with-their-playmates.html http://www.apa.org/pubs/journals/releases/emo-aping-expressions-022811.pdf