Tag Archives: Attraction

The Man Behind the Curtain Turns 1

The Man Behind the Curtain turns 1 today! In the past year, this blog has had over 4800 views from people in 104 nations. This surpassed what expectations I had, and I am looking forward to another good year.

The most popular posts this year were:

Dinosaurs are not Extinct

Hot or Not

Do genes skip generations?

Testing a Claim: Ceramic Knives

The least popular posts were:

Drug-Resistant Diseases

Skipping Generations Part 2

You’re Doing it Wrong, Part 2: Post Hoc Ergo Propter Hoc

A UFO (which was my first post)

And these are my personal favorite posts:

For All Mankind

Dinosaurs are not Extinct

10% of our Brains

The Evolution of Flight

Thanks for reading! I hope 2015 will be even better. (Tomorrow I will go through and fix all of the broken images. Sorry about that.)

Have a topic you want me to cover? Ask in the comments section or on Twitter @CGEppig

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Sexy Symmetry

My recent post on attraction was, by a large margin, my most popular post yet. As this is an area of expertise for me, I’m happy to write more on the topic. This post will discuss in greater detail an aspect of attractiveness that I touched on briefly before: symmetry.

Leonardo da Vinci’s “Vitruvian Man” exhibits high symmetry. Image from http://blsciblogs.baruch.cuny.edu

The human body is designed to have external symmetry. There are certain parts of us that are designed to be asymmetric — e.g. the brain, most of our organs — but for the sake of this conversation, “symmetry” refers to the parts of us that are supposed to be symmetrical. Evolution built our bodies to be perfectly symmetrical on the outside, and there is good reason for this. For example, if our legs were not the same length or equally-muscled, walking around would be inefficient. Overall, our symmetry allows us to have mechanical balance in our bodies, and to interact with our surroundings with both sides of our body (handedness not withstanding).

That we end up basically symmetrical as adults is remarkable. When our bodies grow, they do so by the individual cells in our body dividing, growing, differentiating, and stacking up to form our limbs and organs. This process takes place over one and a half decades, and involves roughly 10 trillion cells in the end product (not counting the trillions that die along the way). A symmetrical body therefore has roughly the same number of cells in the same locations on each half of the body. This is like two cars with blind-folded drivers traveling perfectly parallel and at the same speed for hundreds of miles. But our bodies do not turn out with perfect symmetry. Developmental perturbations, such as injury or disease, can disrupt the intended course of growth. If one of the drivers in my example runs over a small rock, his course and speed will be altered slightly, and he will deviate from the other driver. The number and intensity of these perturbations will determine how different the direction and location of the two drivers will be at any given point.

Thus body symmetry is an indicator of what we biologists call “phenotypic quality.” This is just a fancy way of saying how well-built a body is. Having higher symmetry means that you were able to prevent your body from being disrupted by developmental perturbations. Indeed, people with higher symmetry have higher intelligence, faster reaction time, are more masculine (if male) or more feminine (if female), are healthier, have better mental health, better mental acuity later in life, have higher sperm quality (only in men, obviously), and have better athletic ability. This is not a comprehensive list. The relationship between symmetry and these traits is sometimes small, but there is a clear relationship overall. Symmetry does not cause these traits, but symmetry is related to these traits because they all result from a body that is well-built.

And this is why more symmetrical people are more attractive.

Success in natural selection is about leaving more surviving offspring than other members of your species. If your offspring are put together better than the offspring of other individuals, they will survive better and ultimately leave more surviving offspring themselves. Choosing mates with high phenotypic quality will increase the chance that the chooser’s offspring will have high phenotypic quality. Resistance to disease is an aspect of phenotypic quality that is of particular importance in a mate. Remember from my post on sexual reproduction that an interest in producing disease-resistant offspring is a primary reason why sexual reproduction evolved in the first place.

For this reason, humans are not alone in our preference for symmetrical mates. This preference has been found in many species of birds, fish, insects, spiders, and even plants. The preference for symmetrical mates probably evolved shortly after sexual reproduction did. In my previous post, I list attraction to symmetry as a species-typic trait, but it is typical of way more species than just humans. An interest in high quality mates is integral to sexual reproduction.


The female peahen prefers peacocks that have more symmetrical “eyes” in their tails. This one looks pretty good. Image from http://gallery.photo.net

Symmetry is important, but it is only one trait of many that are involved in attractiveness in humans. As I write more about attraction, I hope the ways in which these traits interact will become more clear.


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Hot or Not

With Valentine’s Day coming up, I thought I’d do a post about the science of attraction. The purpose of this post is not to summarize everything that we know about what makes people attractive to one another, but to explain how we think about it.

First, it is important to realize that attractiveness is not a single trait. Attractiveness is what we call an “emergent property” of many different traits — that is, people may possess many different traits that all add up to making them however attractive they are.

Attractiveness may be broken down broadly into two divisions: physical attractiveness and non-physical attractiveness. Physical attractiveness is the aspects of a person’s body that you find attractive (hands, feet, face, whatever else you’re into), and non-physical attractiveness are the personality, values and social traits of a person.

Another way of breaking down attractiveness is into how broad the preference is for certain traits. Traits may be typical of humans as a species, typical of individual cultures, or individual preferences.

Species-Typic Attractiveness

These are the traits that humans, as a species, tend to find attractive in one another. We can talk about this the same way we talk about any other trait in any other species. For example, the American lobster (Homarus americanus) is usually a reddish-brown color, but about one in two million is instead a brilliant blue color. The presence of the blue lobsters does not change the fact that the typical color of the species is reddish-brown. It just means that there are exceptions to the norm. In humans, the most basic rule of attraction is that men are attracted to women, and women are attracted to men. This is the species-typic trait. But a few percent of humans are either attracted to people of the same sex, to people of any sex, or to no one at all. The existence of these traits — which are far more common than blue lobsters — does not change what is typical of the species, nor are people with these traits any less human. We can tell when an aspect of attractiveness is species-typic when it is common across cultures and throughout time.

The following are examples of other traits that humans tend to find attractive as a species:

Symmetry is a trait that is attractive not only to humans but to many other species. People of both sexes are more attractive when they have more symmetrical faces and bodies. Denzel Washington, people magazine’s sexiest man of 1996, was once found to have an almost perfectly symmetrical face.

Examining the symmetry of Denzel Washington. Image from http://www.pleacher.com

Men are most attracted to women who have a low “waist to hip ratio” or a waist that is narrower than the hips. This is true of people across cultures and time. Waist to hip ratio (or WHR) is calculated by dividing the circumference of the waist by the circumference of the hips. Models and actresses commonly have a WHR of 0.65-0.75.  

Marilyn Monroe’s WHR was 0.63. Image from http://www.dailyhiit.com 

Conversely, women typically find men more attractive who have broad shoulders and relatively narrow hips.

Henry Cavill (as Superman) has an impressive shoulder-to-hips ratio. Image from http://www.healthyceleb.com


Men and women differ in the size of the lower face, and this difference is important in attractiveness. Women with a smaller lower face (relative to the size of the upper face) and men with a larger lower face (relative to the upper face) are more attractive. This is fairly hard to imagine from my description, but the following pictures of Mila Kunis and Nikolaj Coster-Waldau should make it more clear. Pay close attention to the shape of the jaw, the width of the jaw, and the distance from the chin to the nose:

Nikolaj Coster-Waldau. Image from http://www.virtual-history.com

Mila Kunis. Image from http://www.redcarpetnewstv.com

The most universally attractive non-physical trait is niceness. People of both sexes all over the world prefer romantic partners who are nice to them. This probably isn’t a surprise to anyone, but it has been confirmed by science.

Culture-specific Traits

Fashions for clothing, hair styles, facial hair, makeup, and jewelry are vastly different throughout time and space. High heels were originally a mens’ fashion that was later adopted by women. Nowadays a man wearing them is generally considered odd at best. Men used to show their wealth by wearing lots of necklaces and bracelets and rings. Men with wealth are still generally considered to be attractive, but modern, western conventions say “no” to all of the jewelry. Beards were in fashion when my father was young, then they were out for a few decades, now they’re coming back again. The perms of the 80s are mercifully gone, hopefully never to return.

This was all considered attractive in the 80s. Image from www.80sfashion.org

This was all considered attractive in the 80s. Image from http://www.80sfashion.org

Modern fashion often borrows things from fashion of the past, but completely adopting the style of past decades might be a little bit weird. Being weird typically makes one less attractive to others, unless you are in a culture that values being weird.

Some cultures find people more attractive when they are slim and some cultures like full figures.

The human population is the largest it has ever been, and the internet allows people to come together and form new cultures at a rate that has never been seen before. Adopting the conventions of a culture tends to make one more attractive to other members of the culture.

The “bagel head” trend gained limited popularity in Japan a few years ago. Image from global.fncstatic.com

There is limitless variation to what individual cultures may find attractive, but there are no cultures that go against species-typic attractiveness by more than a little bit.

Individual Differences

Individual differences can cover both things that have been studied as well as the wide spectrum of unique things that people find attractive about one another.

People tend to like other people who are like them. This is called “assortative mating.” Political, moral and religious values can be a very important part of this. Liberals tend to date and marry liberals, Muslims tend to date and marry Muslims, vegans tend to date and marry vegans. The same goes for personality traits and even physical traits. There are obviously exceptions, but there is a clear trend.

How we feel about a person’s personality and behavior can influence how physically attractive we find them, and vise versa. If you have a negative experience with a person who is otherwise physically attractive, you will find them less physically attractive or even physically repulsive. The opposite is true as well.

Opposites don’t usually attract, but there are notable cases when they do. The most interesting case is probably the region of the immune system called the “major histocompatibility complex” or MHC. Humans and other vertebrates prefer mates who have different genes than their own in this region.

And sometimes there are just oddities that are unique to the individual. A friend of mine in college really liked guys wearing brown pants. There may not be anything substantial to explain about that.

This is just a primer on how scientists think about attraction. The few traits that I list are just examples and are by no means an exhaustive list of what we know (and there is still an enormous amount that we do not know). Of the things that I discuss, there are many nuances that I could not discuss for length. Indeed, whole books have been written on the topic. For more on this topic, see this book and this book and others. I plan to write more on this in the future, as well.

The point of this is not to tell anyone what they should or shouldn’t be attracted to. Everyone is different and the many aspects of attractiveness can interact in endless ways. People are attracted to whoever they are attracted to, even if it’s nobody.

What I hoped to accomplish here is to share a framework for how to think about the topic. The news is full of reports on new findings about human attraction. I hope it will be easier to put these studies into context after reading this post.

And try out this line tonight:

“Hey baby, I’m heterozygous at my MHC loci.”

Have a topic that you want me to cover? Let me know in the comments section.

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