Size matters in politics: America hasn’t seen a president shorter than 5’7” since William McKinley. A main culprit, unbeknownst to many, comes from voters’ cognitive biases—the work of evolution. And the conundrum took a theatrical turn early this year when Marco Rubio, a Republican presidential hopeful, was spotted wearing a pair of new boots.

“Marco Rubio’s Republican rivals literally are hot on his heels,” opened a New York Post news article on January 6. Speculations followed as to how expensive the boots were. The Rubio camp wasted no time to clarify that they were nothing more than Men’s Florsheim, costing about $100. But the core of Rubio’s “bootgate” brouhaha wasn’t about luxury; it was about the heels—a whole two inches high. “A vote for Marco Rubio” tweeted Rick Tyler, Ted Cruz’s commuatsnications director, “is a vote for Men’s High-Heeled Booties.”

Why would Rubio sport a pair of, as Rand Paul teased, “cute new boots”? As far as we know, tall men have scores of advantages in life, work, and romance. Among CEOs, for example, 90% are taller than the average man, and only 3% are below 5’7”. In fact, for every inch added to their height, men can get an extra 1.8% (about $800) in wages, an amount duly dubbed by economists as a “height premium.”

Rubio may be aware that since the beginning of the last century, nearly 70% of the presidential campaigns between the two major parties have been won by the taller candidate. This wasn’t always the case, though. In fact, of the presidents elected before 1900, eleven were shorter than 5’9”, and only nine were taller (see the chart). After that, however, all short candidates have lost to their tall rivals—James M. Cox (5’6”) to Warren G. Harding (6’0”) in 1920, Thomas Dewey (5’8”) to FDR (6’2”) in 1944, then to Harry S. Truman (5’9”) in 1948, and Michael Dukakis (5’8”) to George H. W. Bush (6’2”) in 1988.

At 5’10”, Rubio is taller than the average American man. Still, he is 5” shorter than the front-runner Donald Trump, a difference you can easily see on the screen during Republican primary debates. By adding two inches to his stature, he hoped to up his chance—if only his rivals weren’t paying attention.

Do tall men make good leaders—presidents in particular? I pulled out data from Wikipedia.com and did some statistics (such as the Mann-Whitney U test and Spearman’s rank correlation analysis). And I found no relationship whatsoever between height and performance ranking for all elected presidents before 1900. (Obviously, I can’t do so for the period after 1900 because no short presidents have been elected.)

Why have short American presidents suddenly vanished since 1900?

The answer, apparently, lies in the use of images in the media. In fact, the advent of the televised debate in 1960 has ushered in even more public scrutiny on candidates’ looks. As a result, no short or bald candidates have made it into the White House since Dwight Eisenhower. (Perhaps, that’s why Trump is careful about his hair—in case people think he is bald.)

How can a candidate’s physical appearance hold such a strong sway on voters’ choices? Psychologists and behavioral economists will point to the halo effect, where a perceived strength—here, the height of a candidate—eclipses all weaknesses. Why, then, are our cognitive systems so naïve as to swoon for something utterly irrelevant (namely, the body size) of a potential leader?

The answer lies in our evolutionary past. Research shows that in a vast number of animals, from insects to mammals, body size can robustly predict winners when resources and mates are at stake. In primates, alpha males are usually large and assuming. (That’s why, even for a novice, it often takes just a glance to spot them in a bunch.) Not only do they win more fights, but females also fall for them. This process favoring large body size is known as sexual selection, and apparently, it also worked for our Stone-Age ancestors. Even in modern tribal societies, from the Amazons to Papua New Guinea, tall, husky men are still widely preferred as chiefs—or “Big Men,” in Polynesia and other Pacific islands. No wonder our cognitive systems are tuned to looking for tall guys as leaders or mates—the hunks, in our colloquial lingo.

Since 1900, apparently, our liking for hunks hadn’t hit a major hitch until Harding was elected. In appearance, Harding was tall, virile, and gracious with thick eyebrows, wide shoulders, and a deep voice—features that can provoke a feeling of being macho, resolute, and competent. Indeed, he rose from being a small town newspaper editor to an Ohio state senator, a US senator, and finally the president. But just after two years in the Oval Office, Harding’s impressive suite of manly features turned out to be all fake. They did nothing but make him a womanizer. He is called, according to the U.S. News, “an ineffectual leader who played poker while his friends plundered the U.S. treasury.” Even Harding himself confessed, “I am not fit for this office and should never have been here.” When he died, rumors had it that his wife had poisoned him, not out of jealousy but to salvage his reputation from the charges of corruption in his administration.

As the ghost of our evolutionary past lingers on, there is no reason why hunks with Harding’s physique won’t be elected again. If you have any doubt, think about Arnold Schwarzenegger. How much of a halo did he draw from his muscles as a body builder and his fame as an action movie star to win the Californian gubernatorial race in 2002?

It’s disconcerting for all concerned citizens to realize that in our age of television and the Internet, presidential elections share much with pageants for Mr. America. If our guts are all we rely on in the process, even the 5’7” John Adams or the 5’4” James Madison may not stand a chance to be elected today. By forgoing a vast pool of talents from women, short men, and minority citizens (except Obama), how can we find the most capable person to lead our nation? In this sense, putting a woman in the White House will mark a new milestone in American democracy: it can break the entrenched spell—our cognitive biases for hunks—imposed by the ghost of evolution.