Bleating Hearts: If Sheep (And Goats) Could Talk

Bleating sheep
By Laura Reyes
March 11, 2013

As members of the subfamily Caprinae, goats and sheep don’t often get attention on a human evolution based blog site like this one. But it seems like I can’t ignore them any longer, especially not after my e-mail inbox has been inundated with videos of these animals yelling. Much to my astonishment and great delight, a sheep has even taken part in a duet with Taylor Swift in her hit song, “I Knew You Were Trouble”. 

Usually when we think of sheep or goat vocalizations, we don’t think of yelling. We think of some kind of “baaa”-like noise. But, as this video and many others have shown, goats and sheep are capable of producing surprisingly human-like sounds.

If you listen to the vocalizations humans produce, they sound pretty unique compared to other animals. Much of this can be attributed to the morphology of the human vocal tract. In mammals, the vocal tract is made up of the nasal cavity, oral cavity, pharynx (throat region), and larynx (voice box). Humans have the ability to produce vowel sounds in part because the pharyngeal region is elongated, which allows the sound to come out as what we recognize as a clear, full, resonant vowel.

W. Tecumseh Fitch, a professor at the University of Vienna, has researched both animal and human vocal tracts. His research has shown that a number of animals, including sheep and goats, drop their larynx during loud vocalizations. This drop creates a longer space in the pharynx and results in a configuration similar to that seen in humans. When you hear Taylor Swift’s sheep, this is precisely what is happening; the yelling sheep sounds like a human because the shape of the vocal tract is very human-like during the yell.

Although other mammals can produce human-like sounds, they are far from producing human-like speech. Human speech consists of distinct units of sound that are affected not only by the shape and size of the larynx and pharynx, but also by the shape and size of the oral cavity and nasal cavity, along with movement of the tongue. The two vocal tracts are very different, with the human having a vertical vocal tract, a shorter and taller oral cavity, and a large muscular tongue capable of producing precise movements. These morphological differences show why such animals are only able to yell, and not produce more speech-like sounds.

However, recent research from Queen Mary University London has shown that goats have the surprising capacity to develop “accents.” Goat accents consist of a unique way of making calls within a group, and are an example of vocal plasticity. Vocal plasticity is the ability to change the type of sounds an animal produces based on the social environment. In general, goats that were housed together in the same group had calls that were more similar to each other than those of other groups. These findings suggest that vocal plasticity is not unique to large social animals such as primates, dolphins, and elephants, but could be more widespread in mammals.

So…why are all these yelling sheep and goats on this blog? Well, we still aren’t quite sure how human language evolved. Studies like the ones mentioned above give clues about what kind of morphological changes can result in the ability to produce human-like sounds, such as a descended larynx, and also what factors might have led to group-specific social calls. We usually look toward apes and other primates for this kind of information since they are our closest relatives, but looking at other lineages can also tell us a lot about why certain behaviors develop.

I, for one, am hopeful that if we house a sheep or goat long enough with Taylor Swift, it will learn enough of her specific accent to sing her songs in their entirety.

For further reading:

Briefer, E.F. and McElligott, A.G. 2012. Social effects on vocal ontogeny in an ungulate, the goat, Caprus hircus. Animal Behaviour 83: 991-1000.

Fitch, W.T. and Reby, D. 2001. The descended larynx is not uniquely human. Proceedings of the Royal Society B 268(1477): 1669-1675.