Primary voice boxes are being developed at a rapid pace

Scientists have discovered that the larynx, like stem box, of primates is significantly larger relative to body size, has greater variation, and is at faster rates of evolution than in other mammals.

Published in the magazine PLOS Biology and led by academics from Anglia Ruskin University (ARU), Stanford University, and the University of Vienna, the study is the first large-scale study into the evolution of the larynx.

The larynx has three main functions: protecting the airway during feeding, regulating the supply of air to the lungs, and vocal communication. Because of its important role in facilitating social behavior, through vocalization, it has long been believed that the larynx is a key area of ​​evolution, especially in species with highly developed voice communication systems.

The researchers made CT scans of specimens from 55 different species, and produced 3-D computer models of their larynxes. These were studied in addition to detailed measurements, including body length and body mass.

The primates varied in size from a pygmy marmoset (Cebuella pygmaea) weighing just 110g, to a Western gorilla (Gorilla gorilla) weighing about 120 kg. The carnivores range from a 280g common dwarf mongoose (Helogale parvula) to a tiger 180 kg (Panthera tigris).

The study found that, for a given body length, primary larynxes are on average 38% larger than those of carnivorans, and that the rate of evolution of larynx is faster in these species.

There is also more variation in larynx size relative to body size among primates, indicating that primates have greater flexibility to evolve in different ways. Carnivorous follow more of a fixed ratio of larynx size to body size.

Larger of the larynx was also found to be a good predictor of the call frequency of a species, proving the relevance for focal communication of the observed large variations.

Co-lead author Dr. Jacob Dunn, Reader in Evolutionary Biology at Anglia Ruskin University (ARU), said: “This study demonstrates clear differences in the evolution of the larynx between groups of mammals.

“Specifically, we have shown for the first time that the primary larynx is larger, less closely related to body size, and at faster evolution rates than the carnivorous streak novel, which is a well-tuned comparison group, indicating fundamental differences in evolution. of the vocal organ on species. “

Co-lead author Dr Daniel Bowling, an instructor in psychiatry and behavioral sciences at Stanford University, added: “Our study also shows that differences in larynx size predict changes in voice pitch, highlighting the important role of the larynx in vocal communication.This is evidenced by the rich and varied conversations produced by many primate species.

“The results suggest fundamental differences between primates and carnivorans in the forces that limit the size of the larynx, and also highlight an evolutionary flexibility in primates that may help explain why they have developed complex and diverse uses. of the focal organ for communication. This provides an exciting avenue for future studies examining variation among other mammalian groups. ”