Next in importance to vision, we humans are audio beings (L. audire, to hear). This is a great little earner when associated words like audience, audiophiles and auditors are considered. The faunal evolutionary road to hearing has not been easy. Most of the eons have been spent incarnating the invertebrates – and none of these can hear.
Though it is thought that cicadas transfer sound to what passes for a central nervous system by the ruby-like crystal in their big, flat heads. If not, why do they make such a summertime din?
Other arthropods are said to employ a similar system. A moth can detect, with its finely-feathered antennae, the wing whirr of a potential mate from a mile away or more – not strictly sound, but targeted airwaves certainly. The earliest vertebrates, fish, can hear, as every angler knows; even if they too have no ears! All pelagics at least have a sinuous lateral line of nerve fiber stretching from the caudal fin to the heads. As such, they hear with their whole body.
Amphibians were the fist to internalize the ear, a stupendous evolutionary leap for the Green Team. Though cane toads and their cronies only properly hear (like cicadas) their own specific mating frequency; the rest is white sound.
Birds, with their more complex but still internal auditory organs, were the first to discriminate sound; hence their exquisite parallel vocal development. The talking parrot is the best example here – er, the lyrebird’s probably a better one! The first external ears in the parade of animal evolution belong tour own marsupials. The placental mammals further extend the auditory range. Alas, we audile-impoverished humans are now in a devolutionary spiral. Not only can’t we hear UHF and ELF like acutely-tuned bats and whales respectively, we can’t even move our ears like a kangaroo!
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