Let's try this again. WaPo has weighed in. Any deliberate derailing will get TBed.
E. O. Wilson, The Social Conquest of Earth speaks of the Westermarck Effect where adults raised in close proximity the first few years of their lives are rarely sexually attracted to each other. This is true even for non-siblings raised together and does not apply to siblings raised apart. And it is true world-wide. The only exception to this evolutionary incest avoidance strategy is royal families who throughout history have interbred.
The taboo was broadened to cousins culturally. The West won out when cousins stopped kissing looks at this:
Mapping the end of incest and dawn of individualism illustrates this:When the Church banned cousins marrying in the Middle Ages it may have led to some very unexpected results, from rising individualism to more generous blood donation, according to new research.
It seems, perhaps counterintuitively, that the Roman Catholic Church’s rules on marriage have produced not only more children, but also more independent thinking and less conformity among the broader Western population.
If these findings appear a little weird, that’s appropriate. The research is focused on the impact of the Church’s rules on marriage in Western, educated, industrialised, rich and democratic societies – a segment known by the acronym WEIRD.
Jonathan Schulz and colleagues from George Mason University and Harvard University in the US wanted to know why people from WEIRD societies are, well, different.
“Western Europeans and their cultural descendants in North America and Australia tend to be more individualistic, independent, analytically minded, and impersonally prosocial (e.g., trusting of strangers) while revealing less conformity, obedience, in-group loyalty, and nepotism,” the authors write in the journal Science....
And the WaPo comments, New study in Science: Medieval Catholicism explains the differences between cultures to this day:
Church exposure and kinship intensity around the world. (A) Exposure to the Medieval Western (blue) and Eastern (green) Churches at the country level. (B) The Kinship Intensity Index for ethnolinguistic groups around the world. Source: "The Church, Intensive Kinship, and Global Psychological Variation," Jonathan F. Schulz, Duman Bahrami-Rad, Jonathan P. Beauchamp, and Joseph Henrich
...That story begins with kinship networks — the tribes and clans of densely connected, insular groups of relatives who formed most human societies before medieval times. Catholic Church teachings disrupted those networks, in large part by prohibiting marriage between relatives (which had been de rigueur), and eventually provoked a wholesale transformation of communities, changing the norm from large clans into small, monogamous nuclear families.
That cultural overhaul, the researchers argue, prompted tremendous changes to human psychology.
...Countries exposed to Catholicism early have citizens today who exhibit qualities such as being more individualistic and independent, and being more trusting of strangers.
...Marrying a cousin was common practice in the large, close-knit networks of kin that dominated societies before Catholicism, the researchers said, and remains normal in many parts of the world today. Bahmari-Rad, one of the researchers, said that he was raised in Iran, where 30 percent of marriages are to first or second cousins, and that he was surprised when he moved to the United States: “I thought it’s weird that Westerners don’t fall in love with their cousins.”
By contrast, the early Catholic Church was obsessed with preventing incest, even between distant relatives, Schulz said: “Thirteen out of 17 church councils in the 6th century were talking about incest and incest regulation.
...“I think this is really trying to get at where human culture comes from,” Talhelm said. But he wondered whether preexisting differences between Europeans and others laid the groundwork for the transformative church to take root: “Where did the church come from then? What caused the church?”