If you ever found yourself thinking that Sonia Braga or Scarlett Johansson had a sexy chin, or were oddly attracted to the mandible of George Clooney or Brad Pitt, you may be a victim of your genes.
Or not, as it turns out.
Some anthropologists believe sexual selection has driven the evolution of faces toward an ideal set of characteristics -- perfect shape, eyes, chin -- common across many cultures. The face, according to the theory of universal facial attraction, serves as a “reliable signal of mate quality” in our evolutionary drive to replicate our genes in future generations.
But before you spend serious money to sex up your mandible -- as some 20,000 Americans do every year -- you might read a study from Dartmouth College that deals a hard blow to the notion that chin selection is narrowing the comely-homely divide.
There simply is too much geographical difference in chin shape to justify the universal facial attraction theory, according to the research, published this week in PLOS One.
If chin shape were a factor universally, "You would expect people from different parts of the world would have the same chin," said Dartmouth anthropologist Seth Dobson, author of the study.
But when Dobson and fellow researcher Zaneta Thayer of Northwestern University measured 180 human mandibles from the American Museum of Natural History, they found no such common ground. The jaw bones came from indigenous groups in nine geographic regions and were evenly split between men and women. Men did, in fact, have bigger “projecting lateral tubercles,” like Brad Pitt, George Clooney and Charlton Heston -- a finding Dobson had reported in a previous study. But differences among samples were significant enough to cast doubt on the facial attractiveness theory.
Why look at chins? Because we have them, first of all: "No other primates have a chin in the sense of a bony protruberance," Dobson said. "Its adaptive value is mysterious."
And studies have shown that chins are important. Males with broad chins are viewed as socially dominant, regardless of culture, according to some studies. The military, for example, is chock full of neo-Hestons.
But chin preference either is not universal or it has no evolutionary impact, Dobson said.
"I don't think the psychologists are doing anything wrong," he said. "They're doing what they're trained to do, which is to find out if people have facial preferences. We're doing what we're trained to do, which is measure bones. I think both bodies of evidence are valid but they need to be reconciled because they appear to be at odds."
Australia may hold the key to that reconciliation. Not Mel Gibson and Nicole Kidman -- they fall into the Western chin model. But Aboriginal jaw bones have "weaker" chins compared with the remaining samples.
In fact, Hollywood, which has selected for the Gibson and Kidman chin, may prove to be a secret driver of sexual selection: “Recent globalization of Western ideas of beauty and other contemporary cultural factors might be influencing chin shape preferences in ways that are not represented in our historical skeletal sample.