Why did we evolve to hear audio signals at 20 Hz to 20 KHz?

[petrushka.googol]

Within the sub phylum vertebrata class mammalia we have response to frequencies in the range 20 Hz to 20 KHz.

 

In dogs for instance this range is augmented...(may be we need to develop special headphones for pooches).

 

Why this specific adaptation? Is it a "vestigial" function in canines or does it make them more aggressive by nature?

 

Your thoughts....

 

Thanks in advance.

[overtone]

Mammals as group seem to have specialized in sound detection acuity - the fantastically sensitive triple-bone structure of the mammalian inner ear is almost a defining characteristic of mammalia. Different mammals of course take different advantage of the ability - everything from echolocation to subtle social interaction rides on the mammalian ear.

 

As those who have watched wolves (same as dogs) hunt mice in long grass or under snow can attest, their hearing is not vestigial .

 

Whales and elephants hear far below 20hz, btw - down to 14 at least, probably lower.

[petrushka.googol]

Mammals as group seem to have specialized in sound detection acuity - the fantastically sensitive triple-bone structure of the mammalian inner ear is almost a defining characteristic of mammalia. Different mammals of course take different advantage of the ability - everything from echolocation to subtle social interaction rides on the mammalian ear.

 

As those who have watched wolves (same as dogs) hunt mice in long grass or under snow can attest, their hearing is not vestigial .

 

Whales and elephants hear far below 20hz, btw - down to 14 at least, probably lower.

 

Are you trying to suggest that the frequency band is a beneficial evolutionary adaptation? If wolves have a selective frequency range then why do mice not share the same band as their evolutionary response. Why did this take place only on the predatory side of the food chain? Are not the victims deserving of a better fate? And if this was the case, how have they survived so long in spite of adversity? The argument presented above seems to have lacunae that are difficult to fill....

[Greg H.]

The simple anbswer is that there was no selective pressure for us to hear outside that range. There may be individuals even now that are capable of hearing lower or higher sounds, but there's no selective benefit to the extended range, so evolution isn't going to play a part in the distribution of that trait among Humans.

 

Among wolves, it would play a part - wolves that can hear mice better get to eat more often, meaning they get to survive longer to pass on their genes,

[chadn737]

There maybe some tradeoff in evolving heightened abilities in one sense. For instance, loss of many of our olfactory receptors coincided with the evolution of trichromatic vision.

 

http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0020005

[John Cuthber]

Very broadly, the wavelength of sounds you can hear varies with the size of animal you are.

That's to do with acoustics of the ear.

 

There are other factors.

high frequency sound is attenuated rather rapidly as it moves through the air.

So, it makes sense to hear high pitched sounds if you are interested in things that are physically near you.

A mouse can hear much higher frequencies than us, but they would be less use to use because a lot of things we are interested in are far away and so that sound wouldn't reach us.

A mouse isn't interested in what's happening a few miles away because it will never bother to walk that far.

 

Low frequency sound, on the other hand, carries rather better so it's useful to be able to hear it.

However, if you want to know where it is coming from, you need big ears, widely separated.

That's easy if you are the size of an elephant.

It's not so useful if you are human-sized.

 

Finally, it's all very well getting the information which that sound carries, but you need a big enough brain to process it.

Brains are expensive to run (in evolutionary terms) so there's a trade off between the benefit from better hearing, but the cost of processing that data.

[overtone]

It's a bit odd to present such a huge range of detection as if it were a specific adaptation, anyway - mammals as a group can hear sound over a 15 octave range at least, and counting detection of vibration adds another three or four octaves to the low end.

 

That's a much larger range than that of sight - that range of detection would have mammals seeing from infrared to Xrays. It covers a large and central fraction of all the sound produced on the planet. The OP is basically asking why mammals can hear sound.

Edited February 10, 2014 by overtone

[swansont]

It's a bit odd to present such a huge range of detection as if it were a specific adaptation, anyway - mammals as a group can hear sound over a 15 octave range at least, and counting detection of vibration adds another three or four octaves to the low end.

 

That's a much larger range than that of sight - that range of detection would have mammals seeing from infrared to Xrays. It covers a large and central fraction of all the sound produced on the planet. The OP is basically asking why mammals can hear sound.

 

There's a very good quantum mechanical reason why optical detection would be limited at the high end: once you start ionizing molecules, the detection signal changes. At the low end you don't have enough energy per photon to cause an interaction. There's also the issue of diffraction through an aperture limiting longer wavelength detection.

 

From a rudimentary evolutionary perspective it's a matter of where there is going to be light. Not much driving the development of a detection sensitivity where there isn't much light. I suspect these effects drive sound, as well: the response is going to be driven by the part of the spectrum where the sound is and what you can physically construct. Audible waves are between ~17 mm and 17 m which is roughly on scale with the human body. Anything much longer or shorter and we have no physical structure that would be efficient at coupling with the waves. You might expect a shift in the range for larger or smaller mammals, absent any specific modifications to their hearing.

[CharonY]

And the nice thing is that we do find (as expected) that the audible ranges scales with body size, though sometimes certain anatomic tricks (as swansont mentioned) to enhance ranges. It should be noted the audible range is not even and higher amplitudes are needed at the extreme ranges to be perceived. But to give some values that I have handy all in (Hz)

 

mouse: 1000-91,000

rat: 200-76,000

dog: 67-45,000

horse: 55-33,500

Elephant: 16-12,0000