Men’s upper-body strength predicts their political opinions on economic redistribution, according to new research published in Psychological Science, a journal of the Association for Psychological Science.

The principal investigators of the research — psychological scientists Michael Bang Petersen of Aarhus University, Denmark and Daniel Sznycer of University of California, Santa Barbara — believe that the link may reflect psychological traits that evolved in response to our early ancestral environments and continue to influence behavior today.

“While many think of politics as a modern phenomenon, it has — in a sense — always been with our species,” says Petersen.

In the days of our early ancestors, decisions about the distribution of resources weren’t made in courthouses or legislative offices, but through shows of strength. With this in mind, Petersen, Sznycer and colleagues hypothesized that upper-body strength — a proxy for the ability to physically defend or acquire resources — would predict men’s opinions about the redistribution of wealth.

The researchers collected data on bicep size, socioeconomic status, and support for economic redistribution from hundreds of people in the United States, Argentina, and Denmark.

In line with their hypotheses, the data revealed that wealthy men with high upper-body strength were less likely to support redistribution, while less wealthy men of the same strength were more likely to support it.

“Despite the fact that the United States, Denmark and Argentina have very different welfare systems, we still see that — at the psychological level — individuals reason about welfare redistribution in the same way,” says Petersen. “In all three countries, physically strong males consistently pursue the self-interested position on redistribution.”

Men with low upper-body strength, on the other hand, were less likely to support their own self-interest. Wealthy men of this group showed less resistance to redistribution, while poor men showed less support.

“Our results demonstrate that physically weak males are more reluctant than physically strong males to assert their self-interest — just as if disputes over national policies were a matter of direct physical confrontation among small numbers of individuals, rather than abstract electoral dynamics among millions,” says Petersen.

Interestingly, the researchers found no link between upper-body strength and redistribution opinions among women. Petersen argues that this is likely due to the fact that, over the course of evolutionary history, women had less to gain, and also more to lose, from engaging in direct physical aggression.

Together, the results indicate that an evolutionary perspective may help to illuminate political motivations, at least those of men.

“Many previous studies have shown that people’s political views cannot be predicted by standard economic models,” Petersen explains. “This is among the first studies to show that political views may be rational in another sense, in that they’re designed by natural selection to function in the conditions recurrent over human evolutionary history.”

Co-authors on this research include Aaron Sell, Leda Cosmides, and John Tooby of the University of California, Santa Barbara.

This research was supported by a grant from the Danish Research Council and a Director’s Pioneer Award from the National Institutes of Health.

For more information about this study, please contact: Michael Bang Petersen at michael@ps.au.dk or Daniel Sznycer at dsznycer1@gmail.com.