Showing off one's playful side is a strategy men and women have developed to make themselves more appealing to potential mates, a new survey suggests.
A team of US academics surveyed 250 undergraduate students and found that both sexes list "sense of humour", "fun loving" and "playful" among the most important characteristics they look for in a potential long-term partner.
The results could explain why humans continue to play throughout their lives, while most other animals stop doing so when they reach adulthood, the researchers said.
Playful behaviour may provide an evolutionary benefit by displaying desirable qualities such as non-aggressiveness or youthfulness to potential long-term partners, they explained.
Lead author Prof Garry Chick, head of the Department of Recreation, Park and Tourism Management at Penn State, said: "Humans and other animals exhibit a variety of signals as to their value as mates.
"Just as birds display bright plumage or colouration, men may attract women by showing off expensive cars or clothing. In the same vein, playfulness in a male may signal to females that he is nonaggressive and less likely to harm them or their offspring.
"A woman's playfulness, on the other hand, may signal her youth and fertility."
The study built on a previous survey which asked participants about 13 different characteristics which people may find desirable in a long-term partner.
They added three new traits – "sense of humour", "fun loving" and "playful" – to the original survey and found that they ranked second, third and fourth as traits that women look for after "kind[ness] and understanding".
Men ranked a sense of humour as the highest priority, with a fun-loving nature third and playfulness fifth, while putting physical attractiveness only ninth, according to the study in the American Journal of Play.
Prof Chick said: "It seems to us that signalling one's virtues as a potential long-term mate through playfulness is not far-fetched.
"Our results suggest that adult playfulness may result from sexual selection and signal positive qualities to potential long-term mates."