[ncmncm]

Grammatical language, e.g. with subclauses, does appear from evidence thus far to be unique to humans, although whalesong is complex enough that it might yet be found there.

I gather that, since the "universal grammatical structure" was promoted, languages have been discovered that are said to lack any such forms. "Said to", because very few people are reporting on them.

Sorry, for sources I would be doing the same DDGing you will.