From A Death in the Rainforest: How a Language and a Way of Life Came to an End in Papua New Guinea, by Don Kulick (Algonquin Books, 2019), Kindle pp. 36-38:
The first casualty of the villagers’ increased acquisition of Tok Pisin was their competence in other local languages. Before the arrival of Tok Pisin, Gapuners were a highly multilingual people. No one in the surrounding villages bothered to learn their little language—a situation that suited Gapuners just fine since it meant that they could employ Tayap as a secret code that nobody else understood.
To communicate with people from other villages, men and women in Gapun learned the local vernacular languages that those people spoke. During my first long stay in the village in the 1980s, I listened to old people who had grown up before the Second World War confidently speaking two other local languages that were unrelated to Tayap or to each other, and I also heard those old people responding to one or two other languages, which they clearly understood even if they couldn’t speak them.
In the generation born after the war, when Tok Pisin “came up big,” competence in other village vernaculars plummeted. People no longer needed to learn local languages because, at that point, it was easier to communicate in Tok Pisin. Women lagged behind men, and they continued to learn other vernacular languages for another generation, largely because women in the area generally still did not speak Tok Pisin as easily as men did. By the 1970s, though, even Gapun women’s active competence in other vernaculars was eclipsed by Tok Pisin.
Once women started speaking Tok Pisin, they started directing it at their young children. This in itself didn’t necessarily mean very much. Unlike middle-class parents in places like northern Europe and the United States, adults in Gapun don’t spend a lot of time talking to small children. They don’t use language to try to teach their kids anything since they don’t believe that toddlers learn by being taught. And to try to converse with a baby is nonsensical since a baby can’t hold up its end of the conversation and talk back.
But when children, especially girls, start to get pressed into service to help mothers care for a new baby, mothers begin to give the kids orders. And those orders—to fetch firewood, to hand the baby whatever it is crying for, to climb up a tree to get betel nut—increasingly got formulated in Tok Pisin. Women started doing to their small children what men had been doing to boys and young men (and their wives) for decades—ordering them about in Tok Pisin. And indeed, the men who ordered their sons, nephews, and wives around in Tok Pisin learned the language themselves in situations where they had been ordered around in Tok Pisin by white overseers.
In language death, ontogeny recapitulates phylogeny. . . .
This, then, is how a language dies: in Gapun, Tok Pisin was incorporated into the villagers’ linguistic repertoire first at the expense of other village vernaculars, and, ultimately, at the expense of their own vernacular. There has been a steady reduction in the number of languages that villagers command, to the point where their impressive multilingualism has in the course of four generations been reduced to monolingualism. A people who used to command many languages now increasingly command only one. And that one is not their ancestral language, Tayap. It is, instead, Tok Pisin.