Guys with bulldog-like faces have been chick magnets throughout human evolutionary history.
A recent study of the skulls of human ancestors and modern humans finds that women, and thereby, evolution, selected for males with relatively short upper faces. The region between the brow and the upper-lip is scrunched proportionately to the overall size of their heads.
Among the men who fit the bill: Will Smith and Brad Pitt.
In a past study, researchers found a similar facial pattern in chimpanzees, with males having relatively shorter and broader faces compared with females, controlling for body size.
Men with "mini mugs" might have been most attractive to the opposite sex and thus most likely to attract mates for reproduction, passing along the striking features to the next generation and so forth, said lead study author Eleanor Weston, a paleontologist at the Natural History Museum in London.
"The evolution of facial appearance is central to understanding what makes men and women attractive to each other," Weston said. "We have found the distance between the lip and brow was probably immensely important to what made us attractive in the past, as it does now."
Whereas past studies have suggested facial symmetry and facial masculinity play roles in this game of desire, none have provided evidence of an evolutionary shaping of male and female faces.
"I think it's a very nice approach," said Randy Thornhill, an evolutionary psychologist at the University of New Mexico, referring to the study. Though not involved in it, Thornhill agrees with the finding that certain facial features evolved due to sexual selection.
The researchers calculated certain facial coordinates on 68 males and 53 female skulls from a contemporary native southern Africa population ranging in age from infant to 30 years old. Measurements included distances between the point between the eye brows and upper lip and from cheekbone to cheekbone.
Weston and her colleagues also examined facial data from fossil hominin skulls dating back to 2.6 million years ago, unearthed in Kenyan deposits as part of the Koobi Fora Research Project IV. These skulls represented five species: Homo erectus, Homo ergaster, Paranthropus boisei, Australopithecus africanus and Paranthropus robustus. These facial coordinates were then compared with the contemporary coordinates.
In spite of their bulkier bodies (about 15 percent more massive than women's bodies), and similarly broader faces, men have upper faces similar in height to women's faces, the scientists found. But compared with the rest of the head, a guy's mid-face is compressed. The differences held throughout human history.
A simple ratio of upper face length to broadness could serve as a proxy for facial attractiveness, the scientists say in a report on their research published in the online journal PLoS ONE.
The scientists are not certain why today's distinctive male face and its proportions evolved.
"A shorter upper face does serve to exaggerate the size of other face features such as the flare of the cheeks and the size of the jaw, but this might not be why it developed," Weston told LiveScience. "Rather the shorter [and] broader the male face the more ‘masculine’ and the less ‘feminine'—based on biological face changes that take place during growth and development—the individual becomes," she said.
Also, this facial development was accompanied by a shrinking of guys' canine teeth, so men appeared less threatening to competitors, yet attractive to mates.
While the scientists who authored the current study examined skulls and did not specifically study how modern faces fit the findings, the Natural History Museum press officers applied Weston's findings to a "quick and dirty" survey of photos of celebrities.
They came up with a list of stars with masculine faces, listing them from most to least masculine according to facial dimensions: Will Smith, Peter Andre, Justin Timberlake, Thierry Henry, Brad Pitt, David Beckham, Johnny Depp and Kanye West.
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Jeanna served as editor-in-chief of Live Science. Previously, she was an assistant editor at Scholastic's Science World magazine. Jeanna has an English degree from Salisbury University, a master's degree in biogeochemistry and environmental sciences from the University of Maryland, and a graduate science journalism degree from New York University. She has worked as a biologist in Florida, where she monitored wetlands and did field surveys for endangered species. She also received an ocean sciences journalism fellowship from Woods Hole Oceanographic Institution.