All chins are not created equal

(Press-News.org) EVANSTON, Ill. --- That jutting jawline may not be as universally attractive as scientists have assumed.

One of the theories behind universal facial attractiveness (UFA) is that some facial features are universally preferred because they are reliable signals of mate quality. But a new Northwestern University study tests one of the assumptions that the chin, commonly discussed in UFA literature, is consistent in shape across human populations.

Researchers found significant differences in chin shape across populations.

"This suggests that either sexual selection hasn't been important in shaping chin shape in humans or that facial preferences differ between populations," said Zaneta Thayer, a doctoral student in anthropology at Northwestern University and lead author of the study.

The findings also suggest that human mate choices are based on more than just attractiveness.

"We hope that our study will encourage evolutionary psychologists to consider how their research on facial attractiveness actually influences 'evolutionary success' as measured through number of offspring produced," Thayer said.

"By evaluating patterns of variation in actual trait distribution within and between populations, we can get a better sense of what previous selection has actually looked like in these populations."

Thayer's current study builds on previous research she and her co-author Seth Dobson of Dartmouth College conducted in 2010. They evaluated competing theories for the adaptive significance of the human chin. She stressed that humans are the only primates with a chin, one of the unique characteristics that defines our species.

"We found that the indigenous Australian population had the most unique chin shape pattern relative to other populations," Thayer said. "That said, even after removing this population from the analysis, significant differences remained between other populations."

Thayer said researchers should think more critically about whether facial preferences inform us about actual mate success in humans.

"Since humans have evolved to be such socially complex individuals, it is not surprising that their mate decisions are based on more than just attractiveness," she said.

The study, "Geographic Variation in Chin Shape Challenges the Universal Facial Attractiveness Hypothesis," is the first study to examine the universal facial attractiveness theory not using data looking at facial preferences but instead using actual patterns of variation in the shape of traits themselves. Dobson is also co-author of this study. The article appeared in PLOS One April 3.

### NORTHWESTERN NEWS: http://www.northwestern.edu/newscenter/