Over the course of our evolution, our face changed dramatically. One big development was the human nose: it got pointy. It’s a simple change, yet really stands out compared to other apes.

Perhaps their flatter nose is well adapted for getting a finger right in there

Why did we evolve such a simple yet unique change? Maybe it helps us detect disease in our meatier diet. Or could it help heat up the air in the cold climates we now inhabit? However, none of these existing ideas holds up to much scrutiny. For instance, our nose isn’t that great at heating up air, contrary to what you’d expect if that’s why it evolved in the first place.

These failures prompted Lucia Jacobs to explore an alternative reason for why we evolved a unique nose: to help with navigation. Their paper is worth exploring both for presenting an interesting new idea, and for introducing me to the best technical term for the nose ever1.


“External pyramid” is the only nose name I’m using from now on. “I think I’m coming down with something, I have a runny external pyramid”

The human nose and navigation

To understand Jacobs’ “navigational nose” hypothesis, you have to roll the clock back a few million years to when we first got our point external pyramid. Exactly when this happened is debatable, given its soft tissue so doesn’t fossilise. However, changes in the skull suggest it evolved in Homo erectus around 1.6 million years ago2.

This was an important moment in our evolution. Homo erectus was the first habitually upright biped capable of walking long distances (hence the name H. erectus, which means “upright man” and not whatever you childish people are snickering about). In fact, they wound up walking all the way out of Africa.

A reconstruction of Narikotome boy, one of the more famous Homo erectus fossils. Check out their nose!

The fact the nose evolved in this context got Jacobs thinking. The ability to navigate over these new environments would become increasingly important. Particularly given they were shifting to a meat-heavy diet, so must start tracking down prey. Maybe the nose evolved to help with this1.

And this isn’t idle speculation either, upon closer examination it turns out our nose contains many features that could help with navigation. For instance, our two nostrils are more separate than in most other primates. As a result, we have an almost stereoscopic sense of smell, able to tell where scents are coming from. Much like how our two ears help us better pinpoint sounds1.

Whilst this is just a hypothesis at the moment, Jacobs does sketch out a few ways it could be tested. For example, with natural variation in nose shape around the world, we could test whether people with bigger noses can pinpoint the source of smells better.

Nasal index (the ratio of nose height to breadth) around the world1.

Where is the human nose going next?

The variation in the human nose might provide a great opportunity to test this hypothesis, but it also raises a bit of a dilemma. If our nose was so great, why can it be so dramatically different? Surely evolution wouldn’t want to compromise such a vital sensory organ.

Well, as the chart above shows the lower nasal indices occur further north. These higher latitudes are colder, creating sub-optimal sniffing conditions. Thus, Jacobs speculates that those groups were no longer reliant on their nose1.

As such, the narrowing could simply represent neutral mutations building up on the nose; with no natural selection acting to clear them out. This could also explain why the smell receptors in some populations are also accumulating harmful mutations.

The olfactory system has more damaging mutations than other senses

However, Jacobs suspects there might be something more going on.

See, whilst narrow noses might reduce our ability to tell where smells are coming from, they could enhance our ability to detect them. It creates unique air currents inside, spreading out smells so we can better tell what’s under our nose. This could provide an advantage when checking if food is cooked, or sniffing for signs of disease. Both are handy traits in denser farming communities, which many northern populations also happen to live in1.

But again, just like Jacobs’ ideas about why the nose evolved in the first place; this also just a hypothesis. However, like any good hypothesis, it can also be tested. Does variation in nose shape influence smell discrimination?

So we need to carry out a few more tests before we figure out if Jacobs is right. But to test an idea we first need one; making Jacobs’ work invaluable. And again, it’s great for the terminology.

This will never get old

References

  1. Jacobs, L.F., 2019. The navigational nose: a new hypothesis for the function of the human external pyramid. Journal of Experimental Biology222(Suppl 1), p.jeb186924.
  2. Franciscus, R.G. and Trinkaus, E., 1988. Nasal morphology and the emergence of Homo erectus. American Journal of Physical Anthropology75(4), pp.517-527.

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