Ethnic homogeneity (somehow or other construed) is necessary, and indeed important, but not sufficient to a trusting society. If ethnic homogeneity were sufficient to social trust, then all ethnically homogeneous societies would be trusting. Obviously, they are not.
More is needed.
You can trust only those whom you deem to be competent, for one cannot rely upon the incompetent to get things right. Furthermore, you can trust only those whom you deem to be competent to correct moral analyses. I.e., you can trust only those whom you can feel fairly sure have low time preference, which is to say, high intelligence. It takes low time preference to resist the impulse to steal the forbidden cookie from the jar. And it takes high intelligence to infer and to visualize future consequences of present acts, such as the punishment that must eventually arrive in consequence of stealing the cookie. Indeed, it takes low time preference even to cognize fully the notion of future punishment.
High time preference just is the inability to cognize future consequences of present acts in their fullness. If you can’t quite appreciate the hedonic valences of future events, you can’t compute their impact upon present decisions.
There is more. R selected people have high time preference. Where resources are plentiful, there is not much point to investing in capital assets for the future, or therefore in protecting them and respecting their propriety. In a context of r selection, property is therefore insecure, and you cannot trust your counterparties not to defraud or rob you.
So K selection is needed for a trusting society.
Finally, trusting societies are possible only under the aegis of a vital and comprehensive national cult that imposes an absolute moral code upon all its subjects. Only when we can be pretty sure that pretty much everyone we meet considers it not just imprudent or impolitic to defect from the prevalent code, but damnable and contemptible, can we probably trust the stranger in the street.
What is more, a polytheistic cult cannot impose an absolute moral code upon its subjects, for the theomachy that must result from a true polytheism, that does not at all terminate upon the Absolute, cannot but result in conflict of jealous petty cults. Only a cult of the Absolute, the Ultimate, the Universal, and the Total – rather than of the merely local, the parochial, the tribal, the partial – is capable of such an imposition. Only insofar as they are understood to derive from the Absolute Ultimate can absolute moral principles – which is to say, moral principles, properly so called – be discerned and established in the light of its character and operations. This is why there are so very few true polytheisms. It is why almost all polytheisms terminate upon an Absolute Unknown God, whose servants the petty gods more or less are.
An ethnically homogeneous K selected intelligent population with low time preference under a strong national cult of the Ultimate who imposes upon all men an absolute moral code of conduct is sufficient to foster and maintain a trusting society. Nothing less can do.
NB that more may be needed even than that, which has not yet occurred to me.
Note then that capitalism is optimized in a trusting society. In a less trusting society, the friction of transactions is going to be greater, because more will need to be spent on ensuring the fulfillment of all contracts: more insurance, more due diligence, more blood pacts, more laws and lawyers and litigation, more regulation, and so forth – and, not least, a higher bid/ask spread, to cover higher risk of uncertainty. More nepotism, too. Business enterprises in less trusting societies are going to approximate more and more to the tribal businesses we see in the Mafia – the Cosa Nostra.
Ceteris paribus, then, trusting societies are more likely to be prosperous than their less trusting competitors. As less beset by the immediate urgencies of penury, their prosperity will tend to make them also more powerful, enterprising, capable, far-sighted, curious, creative, and interested – all of which will, in turn, tend to make them yet more prosperous.
Also, because they do not need to rely so heavily on familiar bonds of genetic loyalty, trusting societies can afford more social churn, so that men are more easily and aptly sorted into their highest and best use with each generation on the basis of their personal characteristics, and with less regard for their caste of origin. They can afford to be less bound by caste, clan, and family – this, without at all vitiating caste, or clan, or family.
Likewise can they afford to be less bound by law, regulation, and so forth.
So can they rely more on the predominant good faith and commensal fellowship at the sacred altar of their civil interlocutors, and less on the police. So are they more nimble, withal; a handshake, where it be altogether reliable, is lots faster than a formal contract, and less expensive to enact. A fortiori is this so, where violation of contract sealed by a handshake is potential cause for recourse to socially approbated duello; or, at the least, to ostracism, to shunning, to profound disadvantage in all future social transactions.
Given all the foregoing, the historical predominance of the West is not particularly difficult to understand. And, given all the foregoing, the historical predominance of the West is terrifically hard to condemn. It is not somehow unfair. On the contrary, it is given in plain game theoretical logic.