Many species on the planet employ a unique form of com­mu­ni­ca­tion. Birds sing, and dol­phins whistle and click. Yet, despite decades of searching, sci­en­tists have not found any form of animal com­mu­ni­ca­tion that exhibits the struc­ture of human lan­guage, which involves weaving together phono­log­ical patterns.

The reason for this unique trait is still up for debate. Some say humans’ capacity for lan­guage comes from a spe­cial genetic adap­ta­tion. Others say there’s nothing lin­guis­ti­cally spe­cial about the human brain, it’s just bigger and smarter. From our gen­eral increased knowl­edge, com­bined with our unmatched artic­u­la­tory capa­bil­i­ties, we create struc­tured sys­tems of language.

In her new book, The Phono­log­ical Mind, psy­chology pro­fessor Iris Berent revisits the dogma that has long sup­ported the first of these expla­na­tions and presents a com­pelling argu­ment for why things might be a little more nuanced than pre­vi­ously thought.

The argu­ments for the notion that humans’ capacity for lan­guage comes from a spe­cial genetic adap­ta­tion have been based almost entirely on syntax, according to Berent. But this is just one slice of the double layer cake of lan­guage. Syntax is how we put mean­ingful words together to create sen­tences. But even before that, we must form words by com­bining mean­ing­less frag­ments like sound. The capacity to do so is called phonology.

Every known lan­guage uses these two layers to assemble its own method of com­mu­ni­ca­tion. Even iso­lated com­mu­ni­ties of deaf people who were never pre­vi­ously exposed to a con­ven­tional lan­guage even­tu­ally drift toward one that con­sists of both a syn­tactic and a phono­log­ical layer, Berent explained.

At the phono­log­ical level, each human lan­guage fol­lows a spe­cific set of rules. For instance, in Eng­lish we can say “blog” but we won’t say “lbog.” How do we know this? Some lin­guistic rules are learned at an early age. Others, how­ever, might be innately avail­able to all humans. Indeed, many of these rules are sim­ilar across lan­guages. Just as the Eng­lish “pencil” and Spanish “lápiz” each has two syl­la­bles, so do words in sign lan­guages form from pat­terns of syl­la­bles. A person who knows nothing of sign lan­guage is able to track those syl­la­bles in signs, as Berent showed in a paper released yesterday.

To make things even more inter­esting, birds, dol­phins, and most other ani­mals that have been studied also follow spe­cific rules in their own nat­ural modes of com­mu­ni­ca­tion. For instance, birds reared in iso­la­tion will, after a few gen­er­a­tions, come to sing songs that are struc­turally sim­ilar to their species-​​mates out­side the lab. Vervet mon­keys have spe­cific calls for dif­ferent ele­ments of their envi­ron­ment, like snake and eagle, which elicit dif­ferent responses.

The genius of using phonology is that we don’t need so many signs,” Berent said. “We don’t need dis­tinct audi­tory ele­ments for every word we speak; instead, we com­bine and reuse a select group of ele­ments. More­over, dis­tinct lan­guages form those com­bi­na­tions in sim­ilar ways.”

This is what makes human lan­guage spe­cial, Berent argues. It isn’t that we use rules, or that our rules are specif­i­cally adapted for our par­tic­ular mechan­ical chal­lenges. Rather it’s the capacity to com­bine these two ingredients–to form rules that are them­selves designed to adapt to mechan­ical challenges–that is poten­tially unique to human vocal patterns.

Berent believes that phonology is a system of core knowledge—like our innate ability to quan­tify things, or our innate sense of dis­tinct objects. And just like math­e­matics or physics, cul­tures use this core knowl­edge to create sophis­ti­cated the­o­ries and tech­nolo­gies. Human lan­guage is one.