Reputation and trust can solve a lot of business problems, like post-investment hold-up or free riding. It turns out that WEIRDo's (about 12% of the planet) have been successful, in part, because they manage to build and maintain reputations and trust more easily than others.
WEIRDos are more individualistic and independent, less conformist and obedient, more likely to favor “impersonal prosociality” — the idea that one set of moral rules should govern how you treat everyone, from the most distant stranger to your nearest kin. This seems normal to them, but in a global context, WEIRD people really are extremely weird. And as modernity erodes the last vestiges of traditionalism, they are probably getting WEIRDer and weirder by the day.
…More specifically, Western Christianity; the number of years that one’s ancestors were exposed to the medieval Catholic Church correlates pretty nicely with things like social trust, creativity and willingness to do things like donate blood — and correlates negatively with traits such as nepotism.
The world abounds in spurious correlations, of course. But the authors of “The Church, intensive kinship, and global psychological variation” propose a very plausible mechanism: the Catholic Church’s extreme obsession with incest, which isn’t found in the Eastern Orthodox branch. The church kept banning marriages between more and more distant relations, up to sixth cousins, which smashed the tight kin-based networks common to agricultural cultures.