Why are most animal faces eyes at the top, nose in the middle, and mouth at the bottom? How are they all so similar?
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> How are they all so similar?
They all are related to each other.
All animals, in fact all living creatures so far as we can tell, share a common ancestor. All animals came from the same ancestor creature so sharing the same kind of body plan makes sense. Of course not *all* animals have the same kind of facial structure you describe, or even a face at all (starfish for example), but if you are wondering why a squirrel and a cow have the same facial structure it is because their general body plan is inherited from the same kind of creature long ago.
What humans perceive as “most animals,” i.e. vertebrates, is a relatively small group of animals that are all still relatively closely related.
When you start looking at invertebrates, you’ll see that most animals do not have this *exact* facial structure; e.g. the closest thing most insects have to a nose is on *top* of their head.
That said, it’s also because it’s advantageous:
1. Most creatures have a head because it’s advantageous to be able to swivel, angle, and point your sense organs without having to move your whole body.
2. Most creatures have their eyes and mouth on the front(ish) because you want to be able to see where you’re going and what you’re eating.
3. Most animals, lacking hands, need their mouths on the bottom of the face because it would be a huge hassle to turn your head upside-down just to eat something on the ground in front of you.
And there’s your face plan.
As others point out, it depends on whether you’re in the same branch on the tree of life. As a contrast, consider something like the octopus/squid family. Some are quite intelligent, yet look absolutely nothing like us at all. Any aliens we run into are likely to be as different from us as the octopus.
We are deuterostomes, a minority in the animal kingdom, whereas the vast majority of animal life belongs to the Protostome group (e.g. arthropods). The gut plan between the two groups is reversed, which means our “face” developed on the end of the gut plan where protostomes developed an anus, and Vice versa. So while both groups developed a “head” with “eyes” positioned above a “mouth,” that was just an example of convergent evolution, because those features developed from completely different features.
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