a) the villagers know each other.
b) the researcher is the stranger.
those are the teams, researcher vs players, not player one vs player two. when would it make sense to refuse the split, punish a neighbor, and let the stranger keep his money? never.
The thrust of the article is not "this one tribe is an anomaly in how we think and judge", but rather "it turns out that the biggest anomaly is the people in the USA". Up until now the model formed from looking at 'Westerners' has been assumed to be 'the norm' or even how we are physically wired, and unchangeable. Any observed deviations from the model are anomalies and interesting. The novelty here is that actually, things may be the other way around.
Most such experiments carried out in 'the west' are done with strangers. This is a non-trivial difference.
Go to the Ozark mountains in Arkansas and find a small cluster of cabins in the hills where the inhabitants are all family and rarely venture away. Offer the uncle and his nephew the same deal, suddenly the same 'anomaly' will show.
He was saying that if you aren't careful you won't create the same standards when you go to a community. If 30 of us live together and you come in to do a study that is completely different from sampling from a population of tens or hundreds of thousands (as would occur in most Western studies).
>The Machiguenga had traditionally been horticulturalists who lived in single-family, thatch-roofed houses in small hamlets composed of clusters of extended families.
Their living situation is one where they are all essentially family. There would be big social impacts on costing your family money, because of some perceived issue with an unequal split.
They are likely all going to spend 'together' anyway. They are probably bewildered why this weird foreigner doesn't grasp this basic fact, and is forcing them to go through some bizarre ceremony to get the money.