Angela
Elite member
- Messages
- 21,823
- Reaction score
- 12,329
- Points
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- Ethnic group
- Italian
It's usually about property and wealth and the concentration of it, but also, seems that you get a lot more support from a lot more people, which is certainly a big plus.
However, the negatives are extreme, if not for the couple, for their progeny and for society.
Razib Khan talks about a recent paper examining the issue.
See:
https://www.gnxp.com/WordPress/2019...ousins/?utm_source=dlvr.it&utm_medium=twitter
The paper is here:
[h=1]"Associations of autozygosity with a broad range of human phenotypes"[/h]https://www.nature.com/articles/s41467-019-12283-6
"n many species, the offspring of related parents suffer reduced reproductive success, a phenomenon known as inbreeding depression. In humans, the importance of this effect has remained unclear, partly because reproduction between close relatives is both rare and frequently associated with confounding social factors. Here, using genomic inbreeding coefficients (FROH) for >1.4 million individuals, we show that FROH is significantly associated (p < 0.0005) with apparently deleterious changes in 32 out of 100 traits analysed. These changes are associated with runs of homozygosity (ROH), but not with common variant homozygosity, suggesting that genetic variants associated with inbreeding depression are predominantly rare. The effect on fertility is striking: FROH equivalent to the offspring of first cousins is associated with a 55% decrease [95% CI 44–66%] in the odds of having children. Finally, the effects of FROH are confirmed within full-sibling pairs, where the variation in FROH is independent of all environmental confounding."
We're talking 400 authors, and a sample size of over one million, so I doubt this will be retracted!
From Khan:
"Rather, I want to ask: if inbreeding is so bad genetically and biologically, why is it so common? One of the consequences of the Protestant Reformation is that the Roman Catholic Church’s strict enforcement of consanguinity rules were dropped, and cousin marriage became much more common among elites (such as the Darwin-Wedgewood family). The material rationale for cousin marriage is actually rather straightforward, in that it keeps accumulated property and power within the extended lineage. Marriages between children of brothers may cement alliances, while matrilocality and marriages between cross-cousins in South India have been associated with lower domestic abuse rates (in contrast, in North India strongly enforced exogamy has been associated with the idea that women marry into an alien household).I would suggest perhaps that though marriages between relatives are biologically disfavored, there are many cases where it is culturally beneficial. In societies where collective family units engage in inter-group competition, some level of consanguinity may benefit cohesion. Other societies where individualism is more operative may exhibit no such incentives."
I think he gives the Church a bit more credit than it deserves in this case. It's true that the Church saw the problem and passed laws to curtail it, contrary to "pagan" practices.
However, depending on the political considerations, you could get it. Look at the poor Spanish monarchy; we know how that turned out.
Also, even for poorer people, it depended on the particular priest. Third cousins of my maternal grandmother, who were first cousins of each other, were still given leave to marry. I think it may have been a case of "anticipation" of marriage vows, if you understand me. The woman was pregnant innumerable times, but only three of her children survived, and of those children one could never have children, one had one, and one had two.
I can't even count the number of times they were held up to me as an object lesson never to let my eyes stray to any of my male first cousins.
Strangely, I read in another recent paper that fertility is very high when third cousins marry, and the biological closeness of couples generally who have high fertility is about at the third cousin level. That makes sense to me. If the two people have very different immunological systems, they're not going to have high fertility.
However, if third cousins continuously intermarry, in the end you're going to have "virtual" first cousins.
However, the negatives are extreme, if not for the couple, for their progeny and for society.
Razib Khan talks about a recent paper examining the issue.
See:
https://www.gnxp.com/WordPress/2019...ousins/?utm_source=dlvr.it&utm_medium=twitter
The paper is here:
[h=1]"Associations of autozygosity with a broad range of human phenotypes"[/h]https://www.nature.com/articles/s41467-019-12283-6
"n many species, the offspring of related parents suffer reduced reproductive success, a phenomenon known as inbreeding depression. In humans, the importance of this effect has remained unclear, partly because reproduction between close relatives is both rare and frequently associated with confounding social factors. Here, using genomic inbreeding coefficients (FROH) for >1.4 million individuals, we show that FROH is significantly associated (p < 0.0005) with apparently deleterious changes in 32 out of 100 traits analysed. These changes are associated with runs of homozygosity (ROH), but not with common variant homozygosity, suggesting that genetic variants associated with inbreeding depression are predominantly rare. The effect on fertility is striking: FROH equivalent to the offspring of first cousins is associated with a 55% decrease [95% CI 44–66%] in the odds of having children. Finally, the effects of FROH are confirmed within full-sibling pairs, where the variation in FROH is independent of all environmental confounding."
We're talking 400 authors, and a sample size of over one million, so I doubt this will be retracted!
From Khan:
"Rather, I want to ask: if inbreeding is so bad genetically and biologically, why is it so common? One of the consequences of the Protestant Reformation is that the Roman Catholic Church’s strict enforcement of consanguinity rules were dropped, and cousin marriage became much more common among elites (such as the Darwin-Wedgewood family). The material rationale for cousin marriage is actually rather straightforward, in that it keeps accumulated property and power within the extended lineage. Marriages between children of brothers may cement alliances, while matrilocality and marriages between cross-cousins in South India have been associated with lower domestic abuse rates (in contrast, in North India strongly enforced exogamy has been associated with the idea that women marry into an alien household).I would suggest perhaps that though marriages between relatives are biologically disfavored, there are many cases where it is culturally beneficial. In societies where collective family units engage in inter-group competition, some level of consanguinity may benefit cohesion. Other societies where individualism is more operative may exhibit no such incentives."
I think he gives the Church a bit more credit than it deserves in this case. It's true that the Church saw the problem and passed laws to curtail it, contrary to "pagan" practices.
However, depending on the political considerations, you could get it. Look at the poor Spanish monarchy; we know how that turned out.
Also, even for poorer people, it depended on the particular priest. Third cousins of my maternal grandmother, who were first cousins of each other, were still given leave to marry. I think it may have been a case of "anticipation" of marriage vows, if you understand me. The woman was pregnant innumerable times, but only three of her children survived, and of those children one could never have children, one had one, and one had two.
I can't even count the number of times they were held up to me as an object lesson never to let my eyes stray to any of my male first cousins.
Strangely, I read in another recent paper that fertility is very high when third cousins marry, and the biological closeness of couples generally who have high fertility is about at the third cousin level. That makes sense to me. If the two people have very different immunological systems, they're not going to have high fertility.
However, if third cousins continuously intermarry, in the end you're going to have "virtual" first cousins.