Big smacker: Kissing may be just evolution's way of securing a pair-boding and establishing potential mate health, say scientists.
CHICAGO: Kissing your sweetheart isn't just romantic: it may be an evolutionary adaptation to boost bonding and check your partner's health status, scientists say.
Scientists documented changes in hormones such as oxytocin, a hormone involved in emotional bonding, and cortisol, a stress hormone, after test subjects kissed their partners.
"There appears to be an adaptive significance of kissing," said Wendy Hill, a neuroscientist at Lafayette College in Easton, Pennsylvania at the American Association for the Advancement of Science's (AAAS) annual meeting in Chicago.
Hormonal ingredients
Oxytocin is one of the key hormonal ingredients scientists are interested in because it relates to pair bonding. At least one study has also found that it increases trust. An association between an increase in oxytocin and kissing may suggest an evolutionary basis for the behaviour as it relates to pair-bonding in people.
"Over 90 per cent of human societies kiss," said Helen Fisher, a research anthropologist at Rutgers University in New Brunswick, New Jersey. "We're finding all kinds of chemical systems at play during courtship."
Kissing might also allow an individual to assess the quality and health of a mate by sampling the chemical makeup of a mate's saliva, she added.
"Men are more likely to like messy kisses," said Fisher. This could be due to the male subconsciously trying to pick up clues about the female's oestrogen cycle to assess her fertility or to pass on trace amounts of testosterone to make her more receptive, she said.
Bonding matters
In a study involving 15 heterosexual couples, one group was asked to kiss for 15 minutes while the other group held hands with their partners and talked. Blood and saliva samples were taken before and after the 15-minute session.
What researchers found was surprising. Males showed an increase in oxytocin levels after kissing, while oxytocin levels in females actually decreased.
What this translates to is an increase in bonding for the men but a decrease for the women. It was expected that both genders would show an increase, though there was speculation that the setting for the experiment - in a laboratory - wasn't conducive to relaxation and romance, said Hill, which could affect women more than men.
What wasn't surprising was that both groups showed a decrease in cortisol, a stress hormone.
