The authors favorably mention Bernard Chapais’ idea that reciprocal exogamy was important to the emergence of cooperation between groups, as such cousin marriage likely didn’t occur among their study populations.

I can’t imagine an endogamy practicing family faring too well when within a greater group of HGs that they were unrelated with.

re: sexual vs. asexual. there is a big short term gain in asexuality. so that lineages are always speciating toward this lifestyle. but it seems that over the long term these asexual lines go extinct fast. asexual lines tend to be derived, indicating they’re young. the connection to the model i’m positing for incest is that there may be short term gains for human groups which are hyper-endogamous in terms of cohesion. but over the long term they aren’t genetically sustainable. e.g., a disease could wipe them out really quickly.

in terms of mutational meltdown, the samaritans seem to be close that. they’re changing their attitudes to intermarriage with non-samaritans because of this. the parsis too.

Then again, the need to a very expansive on average (albeit prone to false positives and false negatives) rule to control inbreeding may be appropriate in a relatively genetically homogeneous population at the tail end of multiple serial founder effects.

“This is analogous to the macroevolutionary patterns with sexual vs. asexual lineages. The latter tend to be found near the “tips” of phylogenies as derived lineages; a strong clue that they are ephemeral, and tend toward extinction. Yet at any given time asexuality can seem common because it is an effective short-term strategy.”

A little bit more of a foundation to establish in what kinds of situations you see asexual v. sexual lineages, how they are related to modern human reproduction in inbred communities, and what implications are associated with asexually reproducing population have would be helpful in understanding this analogy.

I recall Razib talking about some of this many months ago in the context of genetic load dropping that might have parallels to mixed mode reproduction (perhaps in the context of Game of Thrones analysis?) and found it to be fascinating and thought provoking. It was a new idea I’d never considered.

But, I’m having trouble remaining confident that I’m still really getting the point being made as I try to make the leap in this fairly short post from thinking about the Westermarck effect and to reaching back in my memory to actually recall the points made in the earlier post about the implications that arise from animals with mixed mode reproduction.

“Addendum: Just to be clear, I am implying here there may be multiple reasons for incest aversion. A functional model regarding the balance between genetic and anthropological factors would operate at the level of the group and meta-populations.”

If I’m I understanding this addendum correctly, the gist of it is that community-wide mutational melt down wipes out incest tolerant communities thereby continually thinning out the ranks of incest tolerant communities a manner distinct from the Westermarck effect.

If I have understood this statement correctly, are there any anecdotal examples of this happening? I can recall a couple examples where this arguably happened in elite superstates (Hapsburg inbreeding in Europe associated with hemophilia, and ancient Egyptian royal inbreeding leading to health problems like those seen in King Tut).

But, I’m hard pressed to recall even a single historic example of a community experiencing mutational meltdown in the community as a whole (with the possible example of post-isolation by water Tasmania, but that seemed more like a simple loss of critical mass population leading to technological degredation thing).

If I haven’t understood this statement correctly, what am I missing?

I see, sorry about that.

Anyone knows if there’s statistics on how “inbred” countries are? All I have been able to find is statistics of consanguineous marriages.

http://www.consang.net/index.php/Summary

In Hindu society there is a concept of a “Gotr” which is basically a clan of people who have descended from a common male ancestor (sometimes mythical). I think the above statement fits pretty well with how the orthodox population sees matrimonial alliances on a greater scale. In North India, you hear about honor killings of sons/daughters often over the fact that they were of the same ‘gotr’. Something similar is popular as well in South India (at least in Telegu and Tamil anecdotally) where marrying cousins from the matrilineal side is a ‘good’ thing. Actually, it’s a lot more complicated than that, and I don’t know if anyone cares to know.

There is a problem with Pakistani immigrants from some communities and inbreeding. There is a claim is that this is done to bring the whole family over to the UK. A couple of press cuttings below.

700 children born with genetic disabilities due to cousin marriages every year

It’s my choice…

It really is OK to fancy your cousin

breeding antagonism – It’s islamophobia

I am sure this is a reflection of cultural difference then. In the US, inbreeding is generally something to be mocked, used as a slur against rural and southern states and lower class citizens. I can’t say there is anything in the way of a national debate on the issue. Perhaps it is a local one with large immigrant populations, but certainly not one that has risen to the national level. It is also an issue amongst certain sects, such as the Amish, but not necessarily due to a cultural tradition where such marriages are encouraged, but because of the fact that few outside that population are willing to live such lifestyles. Because of the apolitical nature of those groups, debate on the issue doesn’t really extend past the community.

Because of the cultural stigma against inbreeding in the US, I never would have guessed it to be a subject of larger social interest in the West, let alone a national debate. Rather I would have assumed it to be more of a passing social interest. But then I don’t get worked up much about social issues, having a rather Libertarian bent. Furthermore, while the relevance to human evolution is obvious, I have seen many other relevant topics garner less interest than this one, hence the nature of my reply. Had I been aware that this was considered a matter of actual debate in other Western nations like the UK, it would have made more sense why there would be a strong interest in it.

My comment was on my surprise on the interest this particular subject seems to garner from reader audience as a whole compared to other topics, which I would have suspected to be of greater general interest.

For human geneticists inbreeding interesting because
With next gen sequencing we can see deleterious mutations have effect. When agreggated we can indirectly observe the effects of mutational load, and get an insight into genetic variation.

It is controversial because we hear from someone like Fox that it’s no big deal because cousin marriage increases the proportion of birth defects from 2% to 4%, and also hear from clinicians who are trying ameliorate the effects of these birth defects on real people.

Students ask: “Why then did our ancestors not all die out as the result of genetic inbreeding?” Good question.

Begging the question. It assumes that his explanation of ubiquitous cousin marriage is correct

The answer is on the one hand that those supposed bad effects only are dangerous if there is bad stock to begin with.

Everyone is bad stock – some people perhaps worse than others, but there will be few individuals without serious deleterious mutations that inbreeding can help to express

On the contrary, if the genetic stock is good, then close inbreeding would perpetuate it. (Think of thoroughbred horses.)

Thoroughbred horses can run fast, They are also extremely temperamental and are prone to a number of genetic diseases. Do we have records of the horses with severe defects that enabled us to breed out any bad traits?

On the other hand, it has been shown that even if genetic diversity is somewhat lowered by inbreeding, small periodic doses of out-breeding rapidly restore it and even speed up evolution.

I suppose this is Sewall Wrights shifting balance

Also, if there are true deleterious effects then those carrying them would rapidly die out and the bad genes with them. The problem would be self-correcting. (See my Red Lamp of Incest.)

For deleterious recessives then inbreeding will increase the speed of selecting out variants. But this is not quick for cousin marriages. I hate to be the person who says “think of the children” but I cannot regard diseased individuals as a fair price to pay for breeding out recessive traits.

Not only were Australian Aboriginal kinship laws ubiquitous throughout the continent (when some other deeply ingrained cultural practices were not), but very strictly and severely enforced.

I have to entertain at least some skepticism about Fox’s certainty on this.