Chomsky views animal minds as only being capable of bounded ranges of expression. On other hand, human language makes use of a finite system of symbols to communicate an infinite array of thoughts and ideas. For Chomsky, there are no intermediate steps between bounded and infinite expression of ideas. The capacity to express an unlimited array of thoughts and ideas stems from a capacity that must have appeared all at once. And this ability must be supported by brain and vocalization structures. Brain structures and an ability to vocalize would either have to already be in place at the time language appeared (because these structures were selected by the evolutionary process for entirely different purposes) or they simultaneously arose with the capacity to conceive of infinite thoughts and ideas. To put it another way, language could not have emerged from animal communication from a step-evolutionary process. It had to appear all at once and be fully intact at the time of its genesis. No one knows of any mechanism that can effect that type of transformation. (emphasis mine)
If the idea that human language "had to appear all at once and be fully intact at the time of its genesis" is correct, then human language is an example of an irreducibly complex system. According to biologist Michael Behe in his book Darwin's Black Box, an irreducibly complex system is "a single system which is composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning" (as quoted in a Nov. 10, 2017 blogpost at the evolutionnews.org website). Behe applied the notion of irreducible complexity to certain biological structures (the classic example being the flagellum of certain bacteria), but its applicability to human language would seem obvious. Human language requires certain basic components--"the capacity to conceive infinite thoughts and ideas," brain structures, and a vocal apparatus--without which it would not function as a system. Arguably language could exist as a purely intellectual capacity in the absence of an ability to vocalize, but then it would be unable to perform one of its most important functions--communication.
What about the other possibility mentioned by Rana in his paraphrase of Chomsky--that the brain structures needed for language and a capacity for vocalization "were [originally] selected by the evolutionary process for entirely different purposes"? This might seem to be a possibility (and I believe Chomsky is open to this view), but it seems to me highly speculative to claim that certain brain structures and the capacity to vocalize somehow become repurposed without any intelligent agent directing this process.
In short, I would argue that Chomsky's view of human language plausibly implies that it is irreducibly complex, and therefore unlikely to have emerged as a result of undirected evolution--even if Chomsky himself would resist this perspective.
Image of Noam Chomsky from Wikimedia Commons