There are a lot of things  that set us apart as humans, like how we walk on two legs and use language.

But today we’re gonna talk about a specific anatomical trait that’s pretty on the nose. It sets us apart from our  closest living relatives, and it’s sitting right there  in the center of our faces.

And you probably already read our title,  so you know I’m talking about the nose. No matter the size or shape of your nose, all human noses are clearly distinct  from those of any other primates. So why do humans have noses that  stick out, but other apes don’t?

Now, nobody nose for sure (sorry) but there are few good hypotheses  as to why our snouts got so big. And these are going to take us all over  our skeleton, from our heads to our toes, and cover a few million years  of evolution in the process. [♪ INTRO] Let’s start with another part of  our bodies that smells… our feet. One other clearly human feature is that we walk upright on two feet,  instead of on all fours.

As early humans gradually stood up  straighter, the shape of our spines changed, from relatively straight and flat like mammals who walk on all fours, into an S-shaped curve. You can even see a similar  change in babies as they grow. Their spines start flat and then  curve more as they get older.

And this is important because of how it changes the way our brain and spine are connected. See, there’s a hole at the bottom of  the skull called the foramen magnum, which literally just means “big hole,” because we like to have fun  with naming anatomical features. That’s the opening where your brain  stem connects to your spinal cord.

And when we started walking upright, that new posture changed the  way we had to hold our heads to keep our faces forward, which also  meant that the foramen had to move. Animals that walk on all four legs, like dogs, have a foramen magnum that sits  further back on their skulls. If our foramen magnum was  as far back as a dog’s is, our natural neck posture would have us staring up at the sky when we were  standing on two legs, which is not good.

And a lot of other stuff had to shift to  allow that foramen to move into place. Generally, human skulls can  be divided into two sections. The upper section is the neurocranium  which surrounds the brain, and the lower section is the splanchnocranium,  consisting of our jaw and nose.

And as you bend the base of a human  skull into an upright position and skootch that foramen forward, it  compresses the size of the splanchnocranium. This reduces the degree that your jaw and lower face sticks out  relative to your upper face. When you compare a chimp’s face with a human’s, the chimp’s teeth are way  out in front of the forehead, but ours are much more in line.

That’s because the chimps have got  much longer, larger jaws than we do. The size and prominence of our jaws  likely decreased because of all of that skeletal rearranging, but also  as a result of our changing diet. You need big strong jaws and  teeth if you have to rely on chewing and grinding a ton of  plants to get your nutrients.

As an example, hominins from the genus  Australopithecus had giant molars that dwarfed our dainty little chompers,  and much larger jaws than ours too. But these guys were pretty  much devoted herbivores. Over time, humans started  hunting and eating more meat, which takes less chewing power than eating plants.

We also started to cook our food, which makes it softer and means that  our jaws had even less work to do. That is what allowed our  jaws to start shortening up; they just didn’t need to be that big,  so why bother keeping them that big? So in terms of our noses, sticking out  is actually a bit of a side effect.

It’s not because our noses  had a reason to move out. It’s because everything below them moved in. And it wasn’t just that our  splanchnocraniums got smaller, our neurocraniums also got bigger.

As the intellectual demands  on early humans increased, our brains grew and so did this part of our skull. Going back to our changing posture, even  just the brainpower needed to balance on two feet could have been a reason  for Homo erectus having a larger brain. So our nose may have also been essentially pushed outwards by our expanding brain.

Some scientists even think  that our protruding nose may act as a radiator, helping cool our brains. The blood vessels in our noses help  dissipate heat, and the act of yawning could stimulate exchange of this cold  blood with hot blood from our brains. So that’s the story of how  every human on the planet got our cute little protruding noses.

The evolutionary story of our honkers  might have seemed simple before, but now you know it’s… snot. Oh my God. They’re for booping!  That’s why we have them: to boop.

Hey, did you know that the reason  you get to watch this is because there’s a bunch of people over on  Patreon who make this channel possible? Without them, there would none  of the unhinged, corny nose puns. With their support (and  possibly yours - I don’t know, maybe you’re one of our patrons) we can sniff out stories like this one to bring them to all of you.

Our patrons also get access  to a ton of neat perks, like a monthly patron-only podcast, blooper  reels, and our private Discord server. To learn more, head on over to  Patreon.com/SciShow. [♪ OUTRO]