Syntax Evolution: Problems and Recursion

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DOI: 10.6084/m9.figshare.4956359


In this paper I argue that syntax and problem solving co-evolved in humans towards Turing completeness. An argument that I thought it should appeal linguists is based on the evolutionary anomaly of syntax, which says that "we are syntactically too competent for syntax": Why would evolution select and keep a capacity to generate and parse any language, when generating and parsing one language would be enough to survive? Why would evolution select and keep our undecidable Turing complete syntactic capability to perform a much simpler decidable syntax?

Against my optimistic assumption, the anomaly of syntax did not appeal linguists, or at least not those reviewing for the journal Biolinguistics. Following Chomsky, they resolve the anomaly by concluding that syntax does not have an evolutionary cause. Though defending that a complex system as language has not an evolutionary cause is as controversial as defending that a complex organ as the eye has not an evolutionary cause, it is a possibility, I would rather say a remote possibility, to which biolinguists adhere.

So they rejected my way out of the anomaly of syntax, which is based on two identities: syntax is computing, by Chomsky, and problem solving is computing, by Turing.

Chomsky's and Turing's identities figure

Then our computing machinery would have evolved to satisfy requirements coming both from syntax and from problem solving; in other words, syntax and problem solving co-evolved in humans. And though syntax does not require Turing completeness, full problem solving does. And full problem solving requires universal computability, which is the maximum computing requirement, and hence the maximum syntactic requirement. So full problem solving needs syntax, and needs all of it: full problem solving needs a complete syntax.

Complete Identities figure


To investigate the evolution of syntax, we need to ascertain the evolutionary rôle of syntax and, before that, the very nature of syntax. Here, we will assume that syntax is computing. And then, since we are computationally Turing complete, we meet an evolutionary anomaly, the anomaly of syntax: we are syntactically too competent for syntax. Assuming that problem solving is computing, and realizing that the evolutionary advantage of Turing completeness is full problem solving and not syntactic proficiency, we explain the anomaly of syntax by postulating that syntax and problem solving co-evolved in humans towards Turing completeness. Examining the requirements that full problem solving impose on language, we find firstly that semantics is not sufficient and that syntax is necessary to represent problems. Our final conclusion is that full problem solving requires a functional semantics on an infinite tree-structured syntax. Besides these results, the introduction of Turing completeness and problem solving to explain the evolution of syntax should help us to fit the evolution of language within the evolution of cognition, giving us some new clues to understand the elusive relation between language and thinking.


The main version of this paper on the co-evolution of syntax and problem solving is in figshare, with its direct link to the pdf file.

A second version is in the arXiv, with a direct link to the pdf file.

Another version is in The Internet Archive, with its pdf file.

There is an older and obsolete version titled "Resolution Machinery" in Cogprints, with its pdf file.

Última actualización: 2019-08-10.

© Ramón Casares 2019