Louder howler monkeys developed smaller testicles, says study

/ 08:40 PM August 03, 2017

Brown howler monkey. Image: INQUIRER.net stock photo

A group of scientists have discovered that an evolutionary adaptation, which gave some howler monkeys louder calls to better mates, developed small testicles as a result.

The study was done by researchers from Cambridge University and published on the online journal Current Biology under the title “Evolutionary Trade-Off between Vocal Tract and Testes Dimensions in Howler Monkeys”.


These researchers observed that howler monkeys with large hyoid bones in their voice boxes produced loud, low-pitched calls that help to make them seem larger, and therefore more attractive to females.

“As a result of their anatomical modifications, howler monkeys produce exceptionally low-frequency vocalizations for their body size compared with other mammals,” the researchers wrote.


Because these Pavarottis of the howler monkey world had less trouble attracting and creating an exclusive harem of females, they tended to have smaller testicles. This is because there was no need to compete so fiercely with other males when it came to mating.

On the other hand, those less gifted in the vocal department lived in large groups of single males. These males repeatedly mate with females in the group, leading them to develop larger testicles to ensure the impregnation of the female with their offspring. The monkey with more and stronger sperm gets to be the daddy.

In effect, male howler monkeys have developed two strategies to win in the reproduction competition: vocal power and balls size.

While these strategies appear to be effective in prolonging the species, the concept of overcompensation also comes to mind when thinking about the more vocal howler monkeys. Alfred Bayle/JB


What makes a dog man’s best friend? It’s in the genes

Personalized ‘cancer vaccine’ clinical trials show positive results

‘Lost memories’ of Alzheimer’s patients can still be recovered, scientists claim

TOPICS: Cambridge University, howler monkeys, large testicles, loud calls, quiet calls, small testicles
Read Next
Don't miss out on the latest news and information.
View comments

Subscribe to INQUIRER PLUS to get access to The Philippine Daily Inquirer & other 70+ titles, share up to 5 gadgets, listen to the news, download as early as 4am & share articles on social media. Call 896 6000.

For feedback, complaints, or inquiries, contact us.

© Copyright 1997-2020 INQUIRER.net | All Rights Reserved

We use cookies to ensure you get the best experience on our website. By continuing, you are agreeing to our use of cookies. To find out more, please click this link.