This would prioritize looking at more-isolated groups or languages, that may not have had time to adapt the new tools, or by looking back in time at past languages using ancient written sources.
Supporting this expectation, subordinating conjunctions, like "after," "before," and "because of," may have evolved only recently, in historical times, and are probably no more a feature of human language than composite bows are a feature of human technological repertoire. The tools of subordination seem less well developed in the earliest versions of Sumerian, Akkadian, Hittite, and Greek. This makes these languages slow, ponderous, and repetitious to read. Subordination tools seem also to be missing in some living languages, including languages found in Australia (e.g. Warlpiri), the Arctic (Inuit), New Guinea (Iatmul), and the Amazon (Piraha).
This is from The Secret of our Success by Joseph Henrich.
Let's check. Pick a few languages.
"The combination of clauses is in Sanskrit in general of a very simple character; much of what in other Indo-European languages is effected by subordinating conjunctions is here managed by means of composition of words, by the use of the gerunds (994), of iti (1102), of abstract nouns in case-forms, and so on." Sort-of point to Henrich, though I don't think anybody has tagged Sanskrit as ponderous.
There's a .doc file on Navajo that claims they use that gramatical construction. They were isolated from Eurasia long before the Greeks started writing. No points to Henrich.
I started looking up Xhosa and got swamped with English tutorials--and they've had enough contact to have picked up all sorts of things over the past few thousand years--at least one word from Arabic...
So far I'm not thrilled with this section. When he wants to show that one language is more primitive than another, he uses sign languages and whistle languages as examples. I was told that however small the vocabulary of a language was, it was always possible to communicate new concepts even if you had to define new words--so you could translate Plato into any language. Is that true? Still reading...