People with wide mouths are perceived by others to be better leaders than people with narrow mouths, and also perform better on real-world tests of leadership effectiveness in business and politics, according to a study published in the Journal of Experimental Psychology.

There is substantial evidence that physical appearances play a role in who people select as their leaders at the voting booth. Studies have shown that people are surprisingly good at picking out the faces of election winners from around the globe, without recognizing the candidates themselves, simply by looking at their faces. However, exactly what characteristics makes a person’s face look like that of a good leader has remained elusive.

Daniel Re and Nicholas Rule, of the University of Toronto, attempted to answer part of that question in a series of experimental and naturalistic studies focused on measuring the width of leaders’ mouths. In male non-human primates, larger size of the canine teeth is related to greater physical aggression and greater likelihood of success achieving a dominant position in the social hierarchy.

In humans, mouth width is determined by the relative size of the canine teeth. So the scientists suspected that if human perceptions of natural leadership qualities have an evolutionary basis in the ways leadership was established among our primate ancestors, then wider mouths would continue to be equated with the kind of dominant personality associated with good leadership.

In the first study, researchers presented a sample of 48 men and women recruited on the internet with a series of 50 photos of male faces and asked them to rate their perceptions of how successful each of these men would be as a leader. Faces with wider mouths were rated by the study participants as more successful leaders.

To account for differences in other facial features between photos, the researchers then created a series of digital composites, averaging multiple photos together, and digitally manipulated the width of the composite’s mouth. Thirty men and women evaluated the wide and narrow-mouthed versions of the composites side by side and indicated which they would prefer to choose as a leader. The wide-mouthed faces were more likely to be chosen for leadership than their narrow-mouthed counterparts.

The second and third studies examined the widths of real-world business and political leaders’ mouths in relation to measures of their success. First the researchers obtained photos of the CEOs of the top 25 businesses in the US in the year 2005 and assessed the correlation between the width of the business leaders’ mouths and the size of their companies’ annual profits over a five-year period. There was a significant and moderately large tendency for CEOs with larger mouths to be in charge of more profitable companies.

Next, the researchers obtained photos of candidates in US Senate and gubernatorial races between 1995 and 2006 to determine whether mouth width was related to the likelihood of electoral success. There was a small tendency for the candidate with the wider mouth to prevail in Senate races, but not in races for governorship.

The study authors conclude that people may associate wide mouths with better leadership because it reflects a physical characteristic that was important in establishing social dominance in our primate ancestors. Although it is by no means the most important factor in determining who will attain leadership success, there seems to be evidence that people continue to respond to this aspect of facial appearance, almost certainly without being aware of it.

Based on these results, aspiring leaders in business or in politics may want to look in the mirror – specifically at their mouths – for an idea of how likely they may be to succeed.