Hot Or Not: 3 Things Our Brains Find Attractive, According To An Evolutionary Biologist

Dr. Randy Thornhill is an American entomologist, evolutionary biologist, and psychologist who has studied the principles of physical attractiveness in insects and mammals, including humans, for years.

By Paula Gallagher3 min read
Hot Or Not: 3 Things Our Brains Find Attractive, According To An Evolutionary Biologist

In a recent podcast, Dr. Randy Thornhill described three biological markers of attractiveness that humans unconsciously assess when looking for a mate: bilateral symmetry, feminine/masculine features, and carotenoid pigmentation. 

Dr. Thornhill said, “Physical attractiveness, fundamentally, is a health certification. That’s how we judge people’s attractiveness. We don’t think about it consciously. It’s an unconscious calculation of the traits important in health.”

Let’s look at each of these three biological traits and what they tell us about our health.

Bilateral Symmetry and Developmental Health

The first trait that Dr. Thornhill discussed is bilateral symmetry. In order for a person to be considered physically attractive, their facial features, body shape, and movement must have average or above average bilateral symmetry. Why? Well, bilateral symmetry is a measure of developmental health. Perfect bilateral symmetry is very hard to achieve naturally, so the closer a human gets, the more it indicates the quality of their developmental health and functioning abilities. For example, evolution says humans and other forward-moving animals have adapted to have bilateral symmetry as the most efficient way to move and thus is beneficial to survival (if one leg is shorter than the other, you’ll move more slowly and are more likely to be a target of predators).

Many studies have been done that prove that the more symmetrical the face, the more the perceived attractiveness of that face. This holds true across age groups and cultures and ethnicities. Both adults and infants will look longer at symmetrical faces than asymmetrical ones.

Better physical development also allows for better cognitive and neurological development. 

Bilateral symmetry of the face is also correlated with symmetry of the body. (Which makes sense, as your developmental health wouldn’t all go to your face.) Bilateral symmetry is also correlated with what biologists call “mating success” – the number of sexual partners for males. Research shows that the more symmetric the man, the higher number of sexual partners he has. More symmetric men are also more likely to engage in affairs outside their relationship than less symmetric men. And more symmetric men make their female sexual partner achieve orgasm at higher rates. 

Because bilateral symmetry is an expression of developmental health, it’s also moderately correlated with IQ and cognitive development. Dr. Thornhill summarized a study he did with his college students that showed that the higher the symmetry, the higher the IQ. The relationship exists because, theoretically, better physical development allows for better cognitive and neurological development. So it’s totally reasonable when you come across someone who’s both hot and smart – developmentally, they should go hand in hand.

Feminine/Masculine Features and Hormonal Health

Another key trait of attractiveness (and health) is how estrogenized a woman’s features are and how testosteronized a man’s features are – this points to their hormonal and reproductive health.

Dr. Thornhill said, “Estrogen is fundamentally the fertility and reproductive capability hormone of the female mammal. So the more estrogenized she is, the greater her fertility and reproductive capacity is. So that’s what we’re responding to in the physical attractiveness of a female.” If a woman has estrogenized features, that’s external proof that her internal reproductive hormones are sufficient for having babies.

Estrogen is fundamentally the fertility and reproductive capability hormone of the female mammal.

What do estrogenized features look like? Estrogen caps bone growth in the face and the body. This means that women have a reduced lower face, chin, and jaw size. Women have smaller bones and shorter statures. And it influences the waist to hip ratio (smaller waist to larger hips), which is a marker of reproductive capacity.

Testosterone has the opposite effect in male bodies, promoting bone growth in the face and body. Men have larger jaws and facial hair, as well as larger bones (which is probably one of the reasons why women are attracted to taller men, as it means more testosterone). 

Carotenoid Pigmentation and Gut Health 

The first two traits are physical features that are outside our control. We can’t change our symmetry or jaw size (at least not without major plastic surgery). But this third trait – carotenoid pigmentation – is something that we can easily influence.

Carotenoids are “a class of more than 750 naturally occurring pigments synthesized by plants, algae, and photosynthetic bacteria.” It’s the pigment that makes fruits and vegetables yellow, orange, and red, like the beta carotene in carrots and the lycopene in tomatoes. Humans can’t make carotenoids, even though they’re fundamental to our metabolism, so we have to get them from our diet, and we typically consume 40-50 different carotenoids in our diet. 

Incorporating more carotenoid-rich foods into your diet can noticeably improve your facial attractiveness.

But what do carrots and tomatoes have to do with physical attractiveness? Well, when you have excess carotenoids in your diet, your body puts a yellow tint in your skin (in everyone, regardless of ethnicity). That degree of yellow pigment is another important biological attractiveness and health marker that we assess unconsciously. You have to have a healthy gut to absorb carotenoids, so the amount of yellow in your skin is an indicator of your gut health. Gut health is important for your mood, immune system, and metabolism. 

So does this mean that if we just eat more yellow, orange, and red fruits and vegetables we can make ourselves prettier? Yes. Yes, it does. Dr. Thornhill described an experiment in which students incorporated more carotenoid-rich foods into their diets, and in just six weeks, they noticeably improved their facial attractiveness. If you’re going to implement this, just remember to eat carotenoids with fat as they’re fat soluble, and healthy fats and oils will increase the bioavailability of the carotenoids. So be sure to include olive oil on your salad topped with bell peppers, carrots, and tomatoes. 

Closing Thoughts

Despite what the feminists would have you believe, physical attractiveness is not a social construct or a toxic by-product of the patriarchy. By tracking these principles across the animal and the human kingdoms, Dr. Thornhill’s “work points to a profound biological basis for the experience of aesthetic attraction” and shows that “a tremendous amount of that is grounded in instinct.”

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