[1] The first part, "The Evolution of Societies and Psychologies", describes WEIRD (Western, Educated, Industrialized, Rich and Democratic) populations "in broad strokes", according to reviewer Pauline Grosjean.

Westerners, according to reviewer Judith Shulevitz, "identify more as members of voluntary social groups—dentists, artists, Republicans, Democrats, supporters of a Green Party—than of extended clans.

While accounts of modern history frequently argue that the Protestant Reformation created individualism and a belief in rule of law, Henrich argues that edicts by the Church that he calls the "Marriage and Family Program" (MFP) reduced clannishness, making Western Europeans more analytic and individualistic, leading to various intermediating institutions and trust in abstract rules; thus, as Henrich argues in the fourth section, "Birthing the Modern World", the Marriage and Family Program opened the doors for the Reformation,[4] with Protestantism being simply a "booster shot" (in the author's words) for a process the Catholic Church set in motion.

[3] In The Week, the book was billed as "a work of dazzling ambition ... Henrich goes to great pains to back [his arguments] up with a huge variety of 'data points' and statistics.

In a number of places, it looks like Henrich is shoehorning facts into his theory ... but he hits far more than he misses ... the splutters of incredulity you experience are more than made up for by the breadth and chutzpah of the narrative.

Wilson had also discussed the Philip Jenkins book Fertility and Faith (which makes a different argument), and described it as "more focused" than The WEIRDest People in the World.

However, Shulevitz argued, "The big-picture approach soars above the reigning paradigms in the study of European history ... Henrich offers a capacious new perspective that could facilitate the necessary work of sorting out what's irredeemable and what's invaluable in the singular, impressive, and wildly problematic legacy of Western domination.

Khan said the author "makes a strong case that the Christian Church's MFP was the cause for the transformation of Western European society during the medieval period.

Guyatt also said the book insufficiently discusses the wrongs of the west, overly stereotypes non-WEIRD societies, lacks insight into the phenomenon of non-Europeans carrying ideas and practices; and emphasizes "the supposedly discrete nature of culture and [the] virtues of 'weird' thinking" almost to the point of endorsing social Darwinism.