The elephant in the room: Elephant vocal folds may hold clues to human sound production
PostedOctober 17, 2013
Up until a year ago, how an elephant made its guttural infrasonic calls was still a matter of debate, as Christian Herbst, from the University of Vienna, Austria, points out: ‘Some people suggested it’s just like in us humans, so a passive, flow-induced vibration of the tissue in the larynx, and others suggested it’s like purring in cats [requiring neural control].’ Unfortunately, unlike in humans, it’s a little difficult to slide an endoscope down an elephant’s vocal tract to see what’s happening. However, in 2010 an opportunity to settle the mystery arose, when an African elephant sadly passed away at Berlin Tierpark zoo. A collaborator based in Berlin quickly seized the opportunity and collected the larynx from the elephant on behalf of Herbst and Angela Stoeger, also from the University of Vienna. Back in Austria, Herbst and Stoeger were then able to reproduce elephant-like sounds by simply blowing air through the voice box, causing the two vocal folds on either side of the trachea to flap passively in the air, just as they would in humans. Their results were published in 2012; however, as elephant larynxes are few and far between, Herbst decided to dig a little deeper to find out just how similar they are to ours, publishing the results in The Journal of Experimental Biology.
From the outset of his second study, Herbst could already clearly see that the elephant’s vocal folds were very different to ours. Comparing CT-scans of both the elephant’s larynx and a human’s, Herbst noted that the elephant’s vocal folds were orientated at a very acute angle in relation to the air stream, whereas in humans the vocal folds were almost perpendicular to the air stream. This meant that the anterior two-fifths of the vocal folds were sheltered from the airflow. What’s more, even when normalised to tracheal diameter, the elephant’s vocal cords were much longer than a human’s and 180% thicker.