It turns out, there might be a biological cost to being pretty. Primatologists at the University of Western Australia and University of Zurich have discovered that attractive male primates tend to have smaller testicles than average — sometimes, significantly so, reports Phys.org.

"This finding clearly shows that you can be well-adorned or well-endowed, but it's hard to be both," said study co-author Dr. Cyril Grueter.

For many primates, being attractive doesn't necessarily mean being "pretty" per se; it often just means being the most intimidating to other males. Either way, though, the male primates that do the best with the ladies tend to be showier. That is, they possess ornamentation, such as beards, manes, capes and cheek flanges, or various shades of color in their faces and fur.

These features not only grant them greater access to breeding females, but they might be covering up for their lack of potency down there.

Researchers found a notable correlation across 100 primate species — yes, including humans — between ornamentation rating and testicle size. It's a finding that might offer some psychological comfort to the Mr. Averages everywhere who harbor envy for the Brad Pitts of the primate world.

The reason for the smaller testes? The best guess we have is that possessing features that make you more attractive takes up a lot of energy. It's biologically expensive to produce those perfect cheekbones, symmetrical faces, elaborate and colorful beards, etc. It's also expensive, though, to produce large testicles. So it's a trade-off. Since both of these features — being attractive or having large testicles — can contribute to your success in siring offspring, you only need one or the other to get the job done.

What this means is that individuals with larger testicles are probably much more efficient at impregnating the few females they do get a chance with. They produce more sperm, and when they produce a stronger ejaculate, it can flush out the sperm left by others. In other words, size does matter for less attractive males.

It goes to show, we're all at the pinnacle of millions of years of evolution. The traits we possess were passed onto us because they were successful for our ancestors. We may not have it all, but we have what it takes, one way or another.

The drawback of being an attractive male
When it's easier for you to attract females, you don't need as potent equipment.