I was questioning myself on why the position of facial organs (eyes, nose, mouth) is the same for almost all animals on Earth ? Is it because of a common ancestor in evolutionary history ? We don't see animals with a mouth on the forehead and eyes on the chin. This face pattern looks universal, is there some biological cause behind, natural selection?

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    $\begingroup$ There is more diversity than you seem to acknowledge. Consider octopuses, spiders, sea stars, slug, etc... Also, how you define these organs is up to subjectivity. For example, insects have amazing chemical sensory organs on the legs but you probably will not want to call these organs noses, just because it is not in the middle of the face. $\endgroup$ – Remi.b Feb 14 '19 at 21:13
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    $\begingroup$ That being said, the question of how much of it is due to common ancestry and how much of it is due to some selective pressures is still of interest. It appears for example that a head like structure appeared several times in independent lineages if I am not mistaken. $\endgroup$ – Remi.b Feb 14 '19 at 22:03
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    $\begingroup$ If those organs were elsewhere, wouldn't you just call that area the "face"? $\endgroup$ – kmm Feb 15 '19 at 2:25
  • $\begingroup$ Maybe I misused some of my words and I know my statement don't apply to all animals, but for example if you take a human, a bear, a squirrel, a tiger, a goat, etc.. the head structure looks similar (eyes on top, nose below and then the mouth). I know that I simplify a lot but it's to be able to easily explain my question. $\endgroup$ – Peculiar Vale Feb 15 '19 at 9:06
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    $\begingroup$ Most mammals live on land where obstacles to vision come from below (eyes up top see over barriers) and food tends to be low rather than high. Selection pressure would have to outweigh those simple facts. Mammal eyes are in very different spots though. For a cat or human the eyes are in the front to assist depth perception. For a cow they are on the sides so they can see predators from any direction. $\endgroup$ – Bryan Krause Feb 15 '19 at 14:43

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