Teeth, language and racial origins, page-1139

The jury is still out on the evolution of human language.
Reference: Origin of language
The origin of language and its evolutionary emergence in the human species have been subjects of speculation for several centuries. The topic is difficult to study because of the lack of direct evidence. Consequently, scholars wishing to study the origins of language must draw inferences from other kinds of evidence such as the fossil record, archaeological evidence, contemporary language diversity, studies of language acquisition and comparisons between human language and systems of communication existing among animals (particularly other primates). Many argue that the origins of language probably relate closely to the origins of modern human behavior, but there is little agreement about the implications and directionality of this connection.

There are several hypotheses on the evolution of language with identified flaws and issues - see the provided reference.
My understanding is that the Chomsky's single step theory favours the incrementalist view.
New languages like Afrikaans have developed incrementally.
I can't imagine language evolving any other way than including an incremental element unless one-day humans woke up to a fully evolved language