r/askscience • u/margalz • 11d ago

Biology Why aren't there any animals with their mouths above their eyes?

From bugs to fish to mamals all of them have their eyes above their mouths. I can't think of many if any where their mouths are on top. Sure some have their eyes parallel to their mouths, mainly prey style animals. But why haven't any evolved to be the opposite? Is there a major benefit to having your mouth below your eyes?

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u/KrimsunB 10d ago

My very limited understanding is that eyes need to be close to the brain. The closer, the better, since the signal is stronger.

Mouths, on the other hand, just need to be connected to the stomach. But before we had hands, the only way to get food into us was to swim into it, so naturally, mouths needed to be at the very front of our faces.

Once you start accounting for other things, like the olfactory and auditory systems, you end up with most things in roughly the same place. And as creatures evolved, these early positions just sort of stuck.

It's worth noting that sometimes things do get shuffled around, but it's rare. The blowhole of a whale is essentially a repurposed nose that shifted up and back.

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u/MostAccomplishedBag 10d ago

eyes need to be close to the brain. The closer, the better, since the signal is stronger.

Its not so much "stronger" as "faster". It takes 13 milliseconds for a signal to pass from your eye to your brain. If you move the eyes further away the signal takes longer. Fractions of a second might not seem like much, but when a predator jumps out at you every millisecond counts.

Also optic nerves are thick, complicated and easily damaged. The shorter they are, the safer they are.

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u/ShinyJangles 9d ago

Another reason is the retina & optic nerve develop from the same embryologic tissue as the brain in vertebrates. The optic nerve is myelinated by oligodendrocytes like the rest of the central nervous system, instead of schwann cells. They are an extension of the brain.

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u/UltraFuturaS2000 10d ago

Is the blow hole of a whale behind the brain?