This is the tenth Q&A for History of Mankind. Paying subscribers received an email soliciting questions and I got some.
I picked four that I think I can shed the most light upon, and they’re all below. First, let me talk briefly about the cousin marriage debate, and a new paper that appeared in Nature about endogamy in the prehistoric Aegean.
This is a very important debate, because it seeks to elucidate why Indo-European and Aryan societies (that is, those descending culturally and ethnically from the horse-riding steppe herders who moved into temperate Eurasia roughly between 3000 BC and 1000 BC) display such a traditional rejection of marriage with first cousins, and the degree to which this is an evolutionary advantage, given that cousin marriage lowers average IQ and leads to a higher degree of hereditary diseases. I discussed the issue at some length here:
I focused the discussion on the Indo-European Bell-beaker peoples, who were patrilocal and practiced exogamy – that is, they protected property along the male line, like most other societies, but also were very open to exchanging brides between clans and tribes.
“This is a distinct European preference that eventually set societies in the continent apart from those in the Fertile Crescent, which appear to have been more averse to marrying their women to outsiders and over time became more and more open to cousin marriage, the ultimate way to isolate groups from potential hostiles,” I added. A footnote in that piece includes a lot of context:
Livy reports that in ancient Rome marriages within the seventh degree of relationship were not permitted. The ban remained in place by the mid-Republic, reinforcing social cohesion as it decreased clannish propensions. Persistent aversion to cousin marriage appears to have been an Indo-European super-power; in India, Aryan invaders brought with them an aversion with cousin marriage that, faced with cousin-marriage tolerance among the older Dravidian population, only eroded over time: the Manusmriti, a compilation of Aryan laws first written down in around the 2nd century AD, forbids marriage between a man and the daughter of his maternal uncle or paternal aunt; Medatithi, a 10th century commentator on the text, stated that such cross-cousin marriages are against dharma; but Madhava, a 14th century commentator who apparently lived in a part of South India where such marriages were socially accepted, already objected against the ban, citing Vedic passages and custom. As of the 21st century AD, still around 10% of marriages involve first- or second-degree cousins – but early on it was far from an exclusively Indo-European trait: in the 2021 Nature paper “Parental relatedness through time revealed by runs of homozygosity in ancient DNA,” Harald Ringbauer et al looked at genomic data from 1,785 ancient humans who lived in the last 45,000 years, and detected low rates of first cousin or closer unions across most ancient populations, with only around 3% of them being cousins.
To this, the new paper in Nature (by Eirini Skourtanioti et al: “Ancient DNA reveals admixture history and endogamy in the prehistoric Aegean,” Natural Ecology & Evolution, 16.1.23) adds quite helpful detail from other regions.
The gist of it is that in Mycenaean (pre-Classical) Greece, the Aegean Islands and Crete cousin marriage was still somewhat common by the mid-2nd millennium BC possibly because of a persistence of older customs, and was only wiped out when additional Indo-European invasions changed the region again from the late 2nd millennium BC.
That helps explain what happened in Iran: as in India, Aryan invaders brought with them an aversion with cousin marriage that, faced with cousin-marriage tolerance among the older Dravidian population, only eroded over time. The persistence of India’s Vedic tradition, partly through the caste system, made that erosion slow in India, as I explained earlier.
In Iran, however, where Aryan invaders quickly merged with local Dravidians to the point that all Iranians (from the word for “Aryan”) spoke steppe languages by the first half of the 1st millennium BC, some of the early Mazdean texts already recommend “khvetukdas” (marriage between very close relatives) as highly meritorious.
Anyway, I’d like to remind you that you can find all posts divided by chronology and theme in the How to Read a History of Mankind guide:
Now for the questions:
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