The most widespread form of communication between living beings is through chemicals. However, the laws governing these channels of communication are still largely not well understood. In the paper “Compression principle and Zipf’s Law of brevity in infochemical communication”, published in the scientific journal Biology Letters, Antoni Hernández-Fernández, a researcher at the Relational Algorithmics, Complexity and Learnability Laboratory (LARCA) of the Universitat Politècnica de Catalunya · BarcelonaTech (UPC), and Iván González Torre, a researcher at the University of the Basque Country and the Technical University of Madrid, have sought, for the first time, evidence of one of the most well-known linguistic laws, Zipf’s law of abbreviation, in chemical communication.

Zip’s law of abbreviation, or simply brevity law, is the statistical tendency for the most frequent words to be shorter. Pervasive across human languages, does this law also apply to the substances that are used in chemical communication—the so-called infochemicals or semiochemicals? To answer this question, the researchers analysed the Pherobase database and found that, in general terms, it does: the most frequent infochemicals in ecosystems, those that are used by a greater number of species, tend to be shorter carbon chains. However, there is a notable exception when infochemicals are grouped by function: pheromones.

Pheromones are chemical substances used in communication between members of the same species, while allelochemicals are used for communication between different species, with diverse functions in ecosystems. An infochemical can have different functions, that is, it can be used as a pheromone by a species and, for example, as an attractant for another species—which is common in predators of the latter.

According to the study by Hernández-Fernández and González Torre, pheromones, statistically, do not obey the brevity law. This could have several explanations, according to the researchers: “First, the need to increase the complexity and length of substances when communicating with your own species to prevent predators from intercepting your signals and therefore from devouring you.” They also remark that: “Second, the fact that pheromones are not statistically brief may indirectly support the handicap hypothesis—classically formulated by Amotz Zahavi—according to which organisms could tend to waste energy on chemical signals as a strategy of reproductive ostentation”. 

These explanations are pending future work that corroborates the results of this pioneering study, according to the authors, who point out that “specific analyses of the chemical channels of specific ecosystems are necessary, since the Pherobase data mix diverse ecosystems and allow only a general perspective.”

Chemical communication on Earth remains a mysterious field of study, even more so on other planets. The authors highlight that “the presence of infochemicals in the atmospheres of distant planets would be indirect evidence of the existence of life on those worlds.”