Vyvyan Evans makes the case in Aeon (Illustration by Matt Murphy):
How much sense does it make to call whatever inborn basis for language we might have an ‘instinct’? On reflection, not much. An instinct is an inborn disposition towards certain kinds of adaptive behaviour. Crucially, that behaviour has to emerge without training. A fledging spider doesn’t need to see a master at work in order to ‘get’ web-spinning: spiders just do spin webs when they are ready, no instruction required.
Language is different. Popular culture might celebrate characters such as Tarzan and Mowgli, humans who grow up among animals and then come to master human speech in adulthood. But we now have several well-documented cases of so-called ‘feral’ children – children who are not exposed to language, either by accident or design, as in the appalling story of Genie, a girl in the US whose father kept her in a locked room until she was discovered in 1970, at the age of 13. The general lesson from these unfortunate individuals is that, without exposure to a normal human milieu, a child just won’t pick up a language at all. Spiders don’t need exposure to webs in order to spin them, but human infants need to hear a lot of language before they can speak. However you cut it, language is not an instinct in the way that spiderweb-spinning most definitely is.
But that’s by the by. A more important problem is this: If our knowledge of the rudiments of all the world’s 7,000 or so languages is innate, then at some level they must all be the same. There should be a set of absolute grammatical ‘universals’ common to every one of them. This is not what we have discovered. Here’s a flavour of the diversity we have found instead.
Spoken languages vary hugely in terms of the number of distinct sounds they use, ranging from 11 to an impressive 144 in some Khoisan languages (the African languages that employ ‘click’ consonants). They also differ over the word order used for subject, verb and object, with all possibilities being attested. English uses a fairly common pattern – subject (S) verb (V) object (O): The dog (S) bit (V) the postman (O). But other languages do things very differently. In Jiwarli, an indigenous Australian language, the components of the English sentence ‘This woman kissed that bald window cleaner’ would be rendered in the following order: That this bald kissed woman window cleaner.
Many languages use word order to signal who is doing what to whom. Others don’t use it at all: instead, they build ‘sentences’ by creating giant words from smaller word-parts. Linguists call these word-partsmorphemes. You can often combine morphemes to form words, such as the English word ‘un-help-ful-ly’. The word tawakiqutiqarpiit from the Inuktitut language, spoken in eastern Canada, is roughly equivalent to: Do you have any tobacco for sale? Word order matters less when each word is an entire sentence.
The basic ingredients of language, at least from our English-speaking perspective, are the parts of speech: nouns, verbs, adjectives, adverbs and so on. But many languages lack adverbs, and some, such as Lao (spoken in Laos and parts of Thailand), lack adjectives.
More here.