New research suggests that, as with humans, some female monkeys find deep male voices more attractive than their higher-pitched brethren. In a cruel kick in the pants, this research also suggests that – at least with howler monkeys – the deeper the voice, the smaller the testicles.
In a study published in Current Biology, a team of Cambridge University researchers comparing the size of howler monkeys’ hyoid bones (located in the voice box) and testicle size found a trade-off between vocal production and sperm production. A trade-off which has, predictably, been reduced to “calls versus balls.”
The researchers argue that the trade-off occurs because it takes too much energy to produce both a very deep call and a large amount of sperm. Alternatively, they argue that the draw of the deep voice is so alluring that an investment in larger testes is simply not needed.
The researchers also found that males with smaller hyoids tend to have a different social structure than those with larger hyoids. Males with larger hyoids – and correspondingly smaller testes – tend to live in small social groups, often with only one male, in a so-called “harem” social model. In these societies, males need to invest more energy in fending off
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