By Christa Lesté-Lasserre
Men and women are more physically attracted to the faces of people who have higher functioning immune systems that might protect them from diseases over their lifetimes.
“There’s nothing inherently special or beautiful about a face that we find attractive, so the theoretical rationale is that there must be something over the thousands of years of evolution that has been consistently rewarded in our mate choice, and that we find these specific traits attractive,” says Summer Mengelkoch at Texas Christian University in Fort Worth.
“Perhaps it’s a cue to people’s genetic qualities, including their immune function and the ability to pass on that good immune function down to their children,” she said.
Scientists had already determined that people are more attracted to the body odors of people of the opposite sex who have better health. However, studies that didn’t involve the detection of any bodily chemicals like smells have shown inconsistent links between attractiveness and health or immune function.
To investigate further, Mengelkoch asked 159 men and women, averaging 20 years old, to pose for professional headshots in which they had neutral facial expressions and wore no make-up or jewelry. They asked these participants about their health and tested their blood and plasma to check their immune functions.
Next, they recruited another 492 men and women, averaging 25 years old, to rate 25 randomly selected photos. Both heterosexual and homosexual participants were asked to rate the attractiveness of people of the opposite sex, and participants weren’t asked about their gender.
The team found that people with higher ratings of attractiveness also had higher rates of phagocytosis– essentially, of white blood cells that combat disease-causing bacteria such as Escherichia coli – a measure that was “pretty consistently related to facial attractiveness”, says Mengelkoch.
These people also had lower counts of neutrophils, a type of white blood cell essential for phagocytosis, suggesting that their white blood cells were particularly efficient in their pathogen-fighting functions.
The opposite, however, was true for men: men preferred women with lower levels of NK cells. These cells can help fight viruses and tumors, but research has also linked women’s NK cell activity with reduced estrogen levels, as well as possibly lower fertility and higher rates of miscarriage.