Many patterns of behavior are passed from generation to generation simply in force of natural selection: those individuals happening to have such patterns wired in their genes have outsmarted those without them.
The relevant patterns are forced upon us not (directly) by natural selection, but by the ongoing demands of our peers.
Any finite (or effectively specifiable infinite) selection of statements (preferably true ones, perhaps) is as much a set of postulates as any other.
The principle that guides the selection of the syntactical devices within the sentence is that they must perform a semantic function.
If the language faculty has many features that are specific to language itself, it would suggest that the faculty was a target of natural selection.
As HCF note (p. 1572), the two of us have advanced a position rather different from theirs, namely that the language faculty, like other biological systems showing signs of complex adaptive design (Dawkins, 1986; Williams, 1966), is a system of co-adapted traits that evolved by natural selection (Jackendoff, 1992, 1994, 2002; Pinker, 1994b, 2003; Pinker
Modifications of function are ubiquitous in natural selection (for example, primate hands, bear paws, and bat wings are adaptations that evolved by natural selection from the fins of fish), so the fact that a trait was initially shaped by selection for one function does not imply that it was not subsequently shaped by selection for another function.
Thus even if the larynx originally descended to exaggerate size, that says nothing about whether its current anatomical position was subsequently maintained, extended, or altered by selection pressures to enhance speech. The fact that Homo erectus had a spinal cord like that of other primates rules out an alternative hypothesis in which the change was an adaptation to bipedal locomotion.
They also are marked for a syntactic category (verb, preposition, and so on), for obligatory grammatically encoded arguments (agent, theme, path, and so on), and for selection restrictions on the syntactic properties of their complements (e.g. whether each one is headed by a preposition, a finite verb, or a non-finite verb).
HCF’s recursion-only hypothesis implies no selection for speech production in the human lineage.