Humour appears to develop from aggression caused by male hormones, according to a study published in this week's Christmas issue of the BMJ.
Professor Sam Shuster conducted a year long study observing how people reacted to him as he unicycled through the streets of Newcastle upon Tyne. What began as a hobby turned into an observational study after he realized that the huge number of stereotypical and predictable responses he received must be indicative of an underlying biological phenomenon.
The study was an observation of people's reactions to a sudden unexpected exposure to a new phenomenon - in this case unicycling, which at the time few had seen. He documented the responses of over 400 individuals, and observed the responses of many others.
Over 90% of people responded physically, for example with an exaggerated stare or a wave. Almost half responded verbally - more men than women. Here, says Professor Shuster, the sex difference was striking. 95% of adult women were praising, encouraging or showed concern. There were very few comic or snide remarks. In contrast, only 25% of adult men responded as did the women, for example, by praise or encouragement; instead 75% attempted comedy, often snide or combative as an intended put-down.
Equally striking, he says, was the repetitive and predictable nature of the comments from men; two thirds of their 'comic' responses referred to the number of wheels - "Lost your wheel?", for example.
Professor Shuster also noticed the male response differed markedly with age, moving from curiosity in childhood (years 5-12) - the same reaction as young girls, - to physical and verbal aggression in boys aged 11-13 who often tried to get him to fall off the unicycle.
Responses became more verbal during the later teens, turning into disparaging 'jokes' or mocking songs. This then evolved into adult male humour - characterized by repetitive, humorous verbal put-downs concealing a latent aggression. Young men in cars were particularly aggressive. Professor Shuster notes that this is the age when men are at the peak of their virility. The 'jokes' were lost with age as older men responded more neutrally and amicably with few attempts at a jovial put-down.
The female response by contrast, was subdued during puberty and late teens - normally either apparent indifference or minimal approval. It then evolved into the laudatory and concerned adult female response.
The idea that unicycling is intrinsically funny does not explain the findings, says Professor Shuster, particularly the repetitiveness, evolution and sex differences. Genetics may explain the sex difference but not the waxing and waning of the male response.
He says the simplest explanation for this change is the effect of male hormones such as testosterone, known collectively as androgens, which induce virility in men.
Particularly interesting for the evolution of humour is, he says, the observations that initial aggressive intent seems to become channeled into a verbal response which pushes it into a contrived, but more subtle and sophisticated joke, so the aggression is hidden by wit. The two then eventually split as the wit takes on an independent life of its own.