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Why do our nostrils point down while those of most mammals point straight out from their face? (cont.)

Gerald Legg

Hurstpierpoint, West Sussex, UK

I read with interest the reasons previously suggested for why human nostrils point down rather than facing forward. As an undergraduate in the late 1960s, I was told that it was a result of our brains and upright posture. This is connected to the human foramen magnum – the opening in the base of the skull that allows the spinal cord to link to the brain – ending up oriented such that our neck bones ultimately joined with the skull at right angles compared with most other mammals.

Primate brains grew larger and the expanding brain tissue forced the skull forward and downward, flattening the face. This had a number of consequences: the nose was shortened, squished and the nostrils ended up pointing down, resulting in incoming air having to do a U-turn on its way to the lungs; the jaw also shortened and the teeth became crowded.

Simon Dales

Oxford, UK

It looks like the reason for this is because we have such flat faces. Other animals have longer top jaws onto which they can fit their nasal structures. We can’t do this because our jaws are so short, so our nasal cavity needs to bend to fit. Even so, it is still rather short, so it needs an extension. Hence a (mostly cartilaginous) nose.

Thin, bony projections on the front of our bodies aren't a good idea because there is a risk of bashing them on things

Thin, bony projections on the front of our bodies aren’t a good idea because you tend to bash them on things. This is possibly why humans don’t have bacula, otherwise known as penis bones.

The advantage of a flat face is that our heads balance nicely on top of our necks, so we can run or walk long distances in search of dinner. Increased food supply then allowed for larger brains, making us cleverer, so we could invent cooking, which meant we could chew and digest what we eat with less effort. So, jaws and guts got smaller as hominids evolved towards our form. Bodyweight dropped, so more of the energy from food could support even bigger brains, and so on. Oh, and downward facing nostrils keep the rain out too.

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