Monday Micro – could microbes help our understanding of the evolution of language?

By Siouxsie Wiles 28/04/2014

It seems far-fetched, but researchers are claiming that microbes could help us understand how language evolved, specifically combinatorial communication, in which two signals are used together to achieve an effect that is different to the sum of the effects of the component parts. Humans use combinatorial communication when we join words together to give a word with a new meaning. For example, when we hear the word ‘swordfish’, what springs to mind isn’t usually swords and random fishes but a swordfish. Despite the ease with which information can be conveyed using combinatorial communication, it has long been thought to be unique to humans and perhaps some other primates. Until now.

Swordfish or fish with sword?! Cartoon by Aaron Foster (@theGagaman)
Swordfish or fish with sword?! Cartoon by Aaron Foster (@theGagaman)

Research just published in the open access journal PLOS One shows that the bacterium Pseudomonas aeruginosa, also uses combinatorial communication, albeit in chemical form (1). P. aeruginosa is an opportunistic pathogen which can cause a number of nasty disease manifestations; chronic lung infections with P. aeruginosa are a leading cause of death for patients with the inherited genetic condition cystic fibrosis.

P. aeruginosa is known to use a form of communication called quorum sensing* in which the bacterium releases chemical signals which, when they reach a critical concentration, turn on particular genes. Thomas Scott-Phillips and colleagues looked at the different genes switched on in response to two of the bacterium’s quorum sensing molecules when applied individually and then in combination and found that the outcome fitted the definition of combinatorial communication – different genes were switched on when the quorum sensing signals were provided in combination, compared to either signal alone. The researchers conclude by saying that their data suggests that advanced cognitive abilities and large brains are not necessarily the reason why some species, such as Homo sapiens, have combinatorial communication systems while others don’t. In other words, our big brains don’t make us as special as we think!

*For a reminder of what quorum sensing is and how the Hawaiian bobtail squid makes us of it, watch the animation I made with graphic artist Luke Harris and his team:

1. Scott-Phillips TC, Gurney J, Ivens A, Diggle SP, Popat R (2014) Combinatorial Communication in Bacteria: Implications for the Origins of Linguistic Generativity. PLoS ONE 9(4): e95929. doi:10.1371/journal.pone.0095929