is constantly thinking to itself

"Who am I gonna mate with?"

We spend a lot of time thinking about mate choice

because passing on your genes early and often is how you win at being alive.

From an evolutionary standpoint,

it's the most important thing you will ever do, if you do it.

And due to its extreme importance,

it's also very complicated, you may have noticed.

Our general understanding of it comes from Charles Darwin

who proposed that some individuals get more action than others

because of sexual selection.

You've heard of it.

One gender of a species consistently prefers mates with specific traits

so individuals with those traits pass their genes on more often

and spread their genes, and the traits, throughout a population.

Old Charlie was certainly on to something.

Take a look at this peacock

Some would consider this overkill, but to the ladies,

a big frothy rack of feathers shows that a dude is healthy

and has good genes.

So, as a result of sexual selection, male peacocks

have evolved to look like 1970s Las Vegas showgirls.

Humans, like peacocks, have evolved to like some traits more than others,

and these preferences date back to a time when those traits

gave an individual huge survival advantages.

So in most cases, beauty is actually a language

that conveys information about health and fertility.

But if you're thinking that it's all about boobs and big muscles,

think harder.

You know what really turns us on? Bilateral symmetry.

Humans are attracted to people whose bodies and

faces look the same on both sides.

How am I doing? Anybody?

Symmetrical imbalance can mean someone was exposed to

some kind of stressor during early development

that they weren't tough enough to deal with.

Similarly, a low waist-to-hip ratio drives both

dude and lady humans wild.

Where fat is deposited on a body is determined by

sex hormones: testosterone in men and estrogen in women.

Women who produce the ideal amount of estrogen

generally have waists that are about 70% the width of their hips.

Same goes for men and testosterone.

People with this ideal ratio are often less susceptible

to cardiovascular disorders, cancer, diabetes, and

women in this range also have less difficulty conceiving and giving birth.

Now you might be wondering

why will a nice, symmetical guy with an ideal waist-hip ratio

make you feel kind of meh, but he's got your friend

driving by his house three times a day?

Well, one reason could be in our genes.

Everybody gives off subtle chemical signals called pheromones

which gives potential mates a clue to our genetic profiles.

Crazy, right?

Studies have shown that men and women are generally

attracted to pheromones of individuals that are

genetically similar to themselves, with one major exception.

They prefer mates with a different kind of

immune system gene called

Major Histocompatibility Complex, or MHC.

The combo of two variations of the MHC gene

helps a couple's offspring fight off disease better

and our pheromones basically tell mates

which version of that gene we have.

But even after you account for pheromones

and symmetry and ratios, it's complicated.

And people don't make rational decisions, so really

don't bother with those hair plugs or that boob job.

It's complicated.

And yet so awesome.

Thanks for watching this episode of SciShow.

In the comments, tell us what makes you attracted

to a potential mate.

Also if you have any questions or ideas or comments,

you can leave those down in the comments or get in touch with us

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