Syntax Evolution: Problems and Recursion

We are Turing complete, and natural language parsing is decidable, so our syntactic abilities are in excess to those needed to speak a natural language. This is an anomaly, because evolution would not select and keep an overqualified feature. We solve this anomaly by using a coincidence, both syntax and problem solving are computing, and a difference, Turing completeness is not a requirement of syntax, but of problem solving. Then computing should have been shaped by evolutionary requirements coming from both syntax and problem solving, but the last one, Turing completeness, only from problem solving. So we propose and analyze a hypothesis: syntax and problem solving co-evolved in humans towards Turing completeness. Finally, we argue that Turing completeness, also known as recursion, is our most singular feature.