How do you track the evolution of laughter? By tickling an ape

Posted by Emma Woollacott

Portsmouth, UK - Tickling baby gorillas might not seem much like work to you and me, but it's a serious business at the University of Portsmouth, where researchers have been examining the evolution of laughter in great apes.


Like human infants, young apes hoot and giggle when tickled. But can this really be described as laughter? The answer to that question is yes, say researchers.
 
"This study is the first phylogenetic test of the evolutionary continuity of a human emotional expression," said the university's Marina Davila Ross. "It supports the idea that there is laughter in apes."


The researchers painstakingly tickled young orangutans, chimpanzees, gorillas, and bonobos, as well as human infants, and analyzed the sounds they produced. A quantitative phylogenetic analysis of the acoustic data was used to create a 'tree' representing the evolutionary relationships among those sounds - which matched the known evolutionary relationships among the five species based on genetics.


The researchers said that the findings support a common evolutionary origin for human and ape tickle-induced expressions. They also show that laughter evolved gradually over the last 10 to 16 million years.


There are big differences between human humour and gorilla giggles. For instance, chimps can have double the fun by laughing while inhaling as well as exhaling. Humans also use more regular voicing in comparison to apes, meaning that the vocal cords regularly vibrate.


One intriguing finding was that gorillas and bonobos can sustain exhalations during vocalization that are three to four times longer than a normal breath cycle - an ability that had been thought to be a uniquely human adaptation, important to our capacity to speak.


The research will be published in Current Biology.