Roar of the rutting stag: why men have deep voices

The behaviour of rutting stags helps explain why men have evolved descended larynges

Horny beast: a red deer stag roars in Richmond Park, London. Photograph: Dan Kitwood/Getty Images

It’s the rutting season. From Richmond Park to the Isle of Rum, red deer hinds will be gathering, and the stags that have spent the past 10 months minding their own business in bachelor groups are back in town, with one thing on their minds. A mature male that has netted himself a harem is very dedicated. He practically stops eating, focusing instead on keeping his hinds near and his competitors at bay. If you’re a red deer stag, one of the ways you make sure that your adversaries know you mean business – and that you’re big – is roaring. And you don’t let up. You can keep roaring all day, and through the night too, twice a minute, if necessary.

While female red deer prefer the deeper roars of larger stags, roaring also appears to be part of how stags size one another up, before deciding whether or not to get engaged in a full-on physical fight. Most confrontations are settled without locking antlers. In male red and fallow deer, the voicebox or larynx is very low in the throat – and gets even lower when they roar. Strap-like muscles that attach to the larynx contract to drag it down towards the breastbone – lengthening the vocal tract and deepening the stag’s roar. Deepening the voice exaggerates body size. Over generations, stags with deeper roars presumably had more reproductive success, so the position of the larynx moved lower and lower in the neck. When a red deer stag roars his larynx is pulled down so far that it contacts the front of his breastbone – it couldn’t get any lower.

In human evolution, much is made of the low position of the larynx in the neck. So much, in fact, that it has been considered to be a uniquely human trait, and intrinsically linked to that other uniquely human trait: spoken language. But if red and fallow deer also have low larynges, that means, first, that we’re not as unusual as we like to think we are, and second, that there could be other reasons – that are nothing to do with speaking – for having a descended larynx.

The relative position of the larynx tends to be lower in men than in women, and as far as speaking goes, this may actually be a disadvantage. The human female vocal tract is capable of making a larger range of discrete vowel sounds than the male. It’s safe to assume that the comparatively low position of the male voicebox hasn’t evolved to improve the production of intelligible speech. But when we listen to someone speaking, we gain far more information than is contained in just the words themselves. Even though we may not always be aware of it, we size people up by their voices. The deep human male voice, exaggerating body size just as it does in stags, could have come about because women found men with low voices more attractive – perhaps we could call this the “Barry White effect”.

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