Asymmetric Auditory Localization …

… or why owls have wonky ears!

A wonky eared Barn Owl

Wonky Ears!

In this post we looked at the symmetry of the human face, and had some fun with editing photos to make them symmetrical, if a little odd looking.

Today, we’re going to look at a remarkable piece of evolution that has favoured asymmetry (that’s the absence of symmetry) over symmetry.

Although you wouldn’t notice from just looking, many owls, such as the Barn Owl pictured above, have asymmetric ears – that means that they are not symmetrical. Their ears are on different places on their head on the left and right sides of their face – the left ear opening is higher up than the right opening.

Owls are great hunters, coming out at night to seek their prey when, of course, there is little or no light.  In these low light conditions, if owls had to rely solely on their eyes they would soon go hungry.  They do, however, use their ears to great effect.

Listening out for potential prey, sound coming from, say, a mouse to their left, would reach their left ear a fraction of a second before it hit the right ear. The owl’s brain processes this and knows the sound – the prey, supper! – came from the left.

And, with one ear higher that the other (those asymmetric, or wonky, ears), using the same idea, it can tell if the sound came from above or below its line of sight.

So, knowing where the sound came from in the left and right direction, and above or below its line of sight, the owl can pin-point exactly the location of its prey, swoop in for the kill and bag its next meal – good news for the owl, less so for the mouse.

We (and I’m generous here, by that I mean pretty much all living organisms) have tended to evolve symmetrically – two eyes, four (or two, or six, or eight legs) etc. and there are lots of good reasons for this (If you want to find out more, you could do worse than grab a copy of “The New Ambidextrous Universe” by Martin Gardiner – be warned, a bit more ‘in-depth’ than this blog post!), but, through natural selection, some Owls have evolved asymmetric ears (wonky ears to you and me) to great advantage.

So symmetry – or its absence – is more than just an irrelevant, pretty abstraction that we use to make pretty patterns. Its all around us – and should be prompting the question “Why?” whenever we notice something is – or isn’t – symmetrical. The answer may be simple, the answer may be complex, but whichever, answering the question will be satisfying and often fascinating.

Symmetrical Owls (but do they have wonky ears?)

If you enjoyed this blog post you might like to listen to this BBC Podcast – an episode of “The Infinite Monkey Cage” where symmetry is discussed.

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