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What is the evolutionary purpose of the topology of human ears? I understand why the ears may have a funnel-like shape but if the various "hills and valleys" do not amplify incoming sound, what purpose do they have?

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Humans do not have the ability to move their outer ear in response to sound. Many animals can do that, and use it to determine the source of the sound waves. Thus, human outer ears are equipped with many "hills and valleys". It does not provide amplification (because the waves can lose their energy bouncing around the ridges), but rather gives the brain more information about the sources' location in space. The brain calculates that location by determining minute differences in the time it takes for the sound to reach sensory cells in the inner ear on both sides. The shape basically attenuates the raw information. That way you get different properties of the sound wave that enters your ear depending on the angle at which it fell on you outer ear.

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Could you support your answer with references? Have the effects of different pinna morphologies been tested in humans? –  kmm Mar 11 at 13:52
    
Different ears are shaped differently. Does that mean the brain is aware of the topology of the ear and aware of how sound is affected by it? –  AndroidPenguin Mar 13 at 23:46
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Evolution doesn't have a purpose. In that light, it's quite possible for an ear to be poorly adapted to hearing - which in fact it is compared to other species.

Stereo hearing (two ears, so you can better detect where the sound is coming from) is heritage from our ancestors, and I know for a fact it didn't evolve further in humans because there was no evolutionary pressure.

In any case, the topology isn't exclusive to our species and is heritage from our mammalian lineage. At some point in our lineage, the species/individuals who had this topology of the ear were able to gather sound waves better and that affected their survival so they passed on the trait to their offspring. Ear topology didn't evolve in humans.

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Can you provide citations to support your assertions? What makes you certain that the ear in humans has not been subject to selection? I'm not suggesting that it has, but I would like to know if there is evidence to the contrary. –  kmm Mar 12 at 14:03
    
Just take a look at the ear(s) of any great ape. Clearly ear hasn't been changed much within our species and the development took part much earlier in our lineage. –  Dan Horvat Mar 12 at 15:20
    
But we don't know what the ear of the most recent common ancestor of humans and chimpanzees looked like. –  kmm Mar 12 at 15:29
    
No, we don't, because we don't know what the common ancestor is, when it lived, and what it looked like. No fossil has been found. We can only presume ears of this shape are a shared trait derived from the common ancestor, otherwise we'd be saying it evolved independently at least four times. That's next to impossible. –  Dan Horvat Mar 12 at 15:36
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