My HormonologyIf you’re a longtime fan of Hormonology, then you know women aren’t the only ones whose hormones impact them on a daily basis. Men have hormone cycles, too (click here for a quick and useful summary). What’s more, the amount of testosterone they have overall has big impact on their personality. For instance, a “high testosterone” male will typically exhibit traditionally macho traits, such as being assertive, impulsive and flirtatious. And a “low testosterone” male will tend to be more cooperative, patient and shy.

Luckily, evolution made it pretty easy for us to figure out which one is which, for instance, a square, chiseled jaw, thick beard, wide face and small eyes are all signs of high testosterone. And a softer jawline, less facial hair, narrower face and big eyes are all signs of low testosterone. Of course, Mother Nature isn’t without her sense of humor and she likes to throw us a few curve balls, which means you’ve probably met your fair share of guys with a super-thick beard and big eyes. Or a narrow face and sharp jawline.

So, how can you tell what his testosterone level is when the physical messages are mixed? Check out the color of his clothes during a competitive event! In a just-released study in the journal Psychological Science, researchers discovered that men with high testosterone prefer to wear the color red (such as Tiger Woods and his red golf shirt) during a competitive task, likely because it represents dominance and aggression—traits high testosterone guys love. Meanwhile, low testosterone guys opt for other less-threatening colors.