Lead author Colleen M. Carpinella, a graduate student, and senior author Kerri Johnson, an assistant professor of communication studies and psychology at the University of California, Los Angeles, said the feminine features had nothing to do with hair or makeup.
"We weren't looking at hairstyle, jewelry or whether a person was wearing makeup or not," Carpinella said in a statement. "We wanted to get an objective measure of how masculine or feminine a face is, based on a scientifically derived average for male or female appearance."
The faces of male and female politicians were studied for 100 subtle dimensions, including the shape of the jaw, the location of eyebrows, the placement of cheek bones, the shape of eyes, the contour of the forehead, the fullness of the lips and the distance between such features as the bottom of the nose and the top of the lip.
The researchers showed 120 undergraduates photos of 434 politicians from the U.S. House of Representatives and asked them to guess the lawmaker's political party.
When the undergraduates guessed a female politician was Republican, their judgments were 98 percent more likely to be accurate for women with the highest rankings for femininity; when they guessed a politician was a Democrat, their judgments were 58 percent less likely to be accurate for more feminine-looking women. However, the faces of male Republicans, on average, scored as less masculine than the faces of their Democratic counterparts.
Republican representatives whose features ranked as highly feminine were Cathy Rodgers McMorris and Michele Bachmann, while Democratic representatives whose features ranked as less gender-typical were Stephanie Herseth Sandlin of South Dakota and Anna G. Eshoo of California.
Displays of femininity can be problematic for female professionals because past research showed people tend to view women as either competent or feminine, but not both, the researchers said.
The findings were published in the Journal of Experimental Social Psychology.