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Westerfeld effect - the incest avoidance mechanism in our brains works by remembering who we spent our childhoods with and killing all sexual interest in that set of people. It probably works by remembering pheromone complexes. (for obvious reasons.. not a lot of research into how this works, exactly)
 This has a bunch of knock on effects -most notably, almost all incest that does not involve damaged people happens because the kids were raised apart. More commonly, unrelated kids raised together from infancy do not usually knock boots, ever. It is probably also why small tribes almost always practice(d) exogamy or strictly segregated child rearing. Those tribes that did not do at least one of them failed to reproduce.
by Thomas on Thu Nov 8th, 2012 at 02:13:37 AM EST
[ Parent ]
If this was always the case, we wouldn't need laws, would we?
by gk (gk (gk quattro due due sette @gmail.com)) on Thu Nov 8th, 2012 at 02:22:05 AM EST
[ Parent ]
Sexual laws in Europe are largely inherited from a medieval church that did not have modern ideas about when laws are needed. If it is a sin the bible and there is no over-riding reason to allow, then ban.

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by A swedish kind of death on Thu Nov 8th, 2012 at 05:34:29 AM EST
[ Parent ]
I thought the Bible sort of approved of polygamy?
by gk (gk (gk quattro due due sette @gmail.com)) on Thu Nov 8th, 2012 at 05:41:20 AM EST
[ Parent ]
If it's the case that people are not attracted to those they spend their first 6 or so years with, most instances of incest will involve older relatives coercing younger relatives. Incest is easier to prove than statutory rape.

At least that's one possible rationale for such laws.

I distribute. You re-distribute. He gives your hard-earned money to lazy scroungers. -- JakeS

by Migeru (migeru at eurotrib dot com) on Thu Nov 8th, 2012 at 06:01:47 AM EST
[ Parent ]
Can you give us a link to that "Westerfeld effect"? Sorry, Google hasn't heard of it.

And can you assure us there is an identified brain mechanism that functions in that way?

As to exogamy: how, without endogamy including at least first-cousin marriages, did we get to be here?

Given that each individual has two parents, they in their turn two each, and so on in a geometric progression: in 30 or so generations back (Middle Ages), the ancestors of each of us would number more than the entire world population at the time. So it cannot be assumed that there is an exogamous geometric progression. We are necessarily the descendents of far more endogamous unions, in number and in closeness of degree, than we would generally like to admit.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 02:54:21 AM EST
[ Parent ]
Couples had much more then two children in the past...
And he was talking about SMALL tribes...
by vbo on Thu Nov 8th, 2012 at 04:20:11 AM EST
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"Couples had much more then two children in the past..."

So?
Plus, they did not have on average much more than 2 that made it to reproductive age, otherwise the population would have risen much faster.

Anyway, populations in the past had phenomenally high consanguinity. Brittany for several centuries was isolated enough that marriages had of necessity a degree of consanguinity that was similar to first cousins -and indeed marriage between cousins was pretty much the norm. Nevertheless, the rise in genetic disorder, while statistically significant, was too small to be practically detectable (a tiny effect can be significant when the sample population is huge).

It's actually an interesting case because the increase should have been higher based on mere genetic proximity. The most likely explanation was that there were more early miscarriages (ie, before the woman knows she's pregnant), and that they would be more likely when the embryo has a genetic disorder. I don't have a link to the study but I have it in a book -in French, though- Histoire de la notion de gène.

Even today, there are huge pockets of genetic proximities. Laos, which I know well enough, is a clear example. Most of my in-laws married cousins (not necessarily first cousins), some even double cousins (yes, genetic proximity equal to siblings in that case). Yet, despite the pretty big sample population (BIG families), the only disorder I've clearly noticed is a stronger tendency to vote UMP than one would like.

Incest is in the mind -and by that I don't mean to diminish it at all. I don't like, for example, the recent tendency of parents to kiss their children on the lips -and indeed, I've seen adult siblings doing it here in London. I wouldn't mind in Russia, but here it means something else and I don't reckon it's a good idea.

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi

by Cyrille (cyrillev domain yahoo.fr) on Thu Nov 8th, 2012 at 04:59:28 AM EST
[ Parent ]
More childbirth, no doubt, but not more surviving children reaching reproductive age. Population only rose very slowly until recent times:

Anyway, the number of children per couple has nothing to do with it. Each individual child necessarily has one biological mother and one biological father. Going back over the generations, it is numerically impossible to suppose that the parental couple in every case was exogamous. Only endogamy (and polygamy in cultures where it was practised) can reduce the number of ancestors (for example, first cousins have the same grandparents, two instead of four). We are all the descendents of, at least, cousin marriage.

As for Thomas's point about isolated small tribes, it's true that there are often rules to enforce or encourage exogamy, or channel endogamy by a clan system, for example. But

Thomas:

Those tribes that did not do at least one of them failed to reproduce.

is a supposition. It would be interesting to see some hard evidence for it.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 04:59:44 AM EST
[ Parent ]
More childbirth, no doubt, but not more surviving children reaching reproductive age.

True that many would die...but they would have 10 or more children and at least half would survive...so still more...more variety...
by vbo on Thu Nov 8th, 2012 at 07:35:18 PM EST
[ Parent ]
That is because I should have checked my memory first.
Try westermarck <,<
by Thomas on Thu Nov 8th, 2012 at 08:07:31 AM EST
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No, you give us a link.
by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 08:14:41 AM EST
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This isn't something completely obscure.

Westermarck effect - Wikipedia, the free encyclopedia

The Westermarck effect, or reverse sexual imprinting, is a hypothetical psychological effect through which people who live in close domestic proximity during the first few years of their lives become desensitized to later sexual attraction. This phenomenon, one explanation for the incest taboo, was first hypothesized by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891). Observations interpreted as evidence for the Westermarck effect have since been made in many places and cultures, including in the Israeli kibbutz system, and the Chinese Shim-pua marriage customs, as well as in biological-related families.

In the case of the Israeli kibbutzim (collective farms), children were reared somewhat communally in peer groups, based on age, not biological relation. A study of the marriage patterns of these children later in life revealed that out of the nearly 3,000 marriages that occurred across the kibbutz system, only fourteen were between children from the same peer group. Of those fourteen, none had been reared together during the first six years of life. This result suggests that the Westermarck effect operates during the period from birth to the age of six.[1]

But:

Sociologists and anthropologists have criticized the validity of research presented in support of the Westermarck effect and the contention that it serves as an ultimate demonstration for the viability of natural selection theory in explaining human behaviour. For example, a 2009 study by Eran Shor and Dalit Simchai demonstrated that although most peers who grew up closely together in the Israeli kibbutzim did not marry one another, they did report substantial attraction to co-reared peers. The authors conclude that the case of the kibbutzim actually provides little support for the Westermarck Effect and that childhood proximity cannot in itself produce sexual avoidance without the the existence of social pressures and norms.[3]

However, while not mentioned in the Wikipedia article, incest avoidance by at least mothers has been observed in primates (this is where I read of Westermarck before). See for example here.

*Lunatic*, n.
One whose delusions are out of fashion.

by DoDo on Thu Nov 8th, 2012 at 11:09:09 AM EST
[ Parent ]
I think it was up to Thomas to offer the reference, but...

It's hypothetical. The empirical evidence offered is shaky. There seems to be no evidence for brain structures dedicated to this, or of the involvement of pheromones, as Thomas suggests. I think it's fair to call the whole thing conjecture.

A pity kcurie isn't here to talk to us about myth structures concerning incest.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 12:18:23 PM EST
[ Parent ]
I wasn't doing Thomas a service but wrote about it because I heard of it too (I think it was via something on Jane Goodall's research). I don't think the evidence from other primates can be called mere conjecture or shaky. The observed incest avoidance isn't deterministic, but a strong trend. I can't find where Thomas mentioned brain structures dedicated to this (nor do I think it necessary that such will be found – this sounds like excessive reductionism of brain functions), but the pheromones speculation (if it isn't Thomas's own) certainly needs sourcing.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Nov 8th, 2012 at 12:45:27 PM EST
[ Parent ]
Thomas:
the incest avoidance mechanism in our brains works by remembering who we spent our childhoods with and killing all sexual interest in that set of people. It probably works by remembering pheromone complexes. (for obvious reasons.. not a lot of research into how this works, exactly)

As to incest avoidance in primates, it may be that there are observable behaviours. In mammals in general, there is no incest avoidance afaik. Probably the most important point is that males move around, favourising gene distribution. I suspect this may explain, in humans, the difference between isolated endogamous communities, where genetic defects become apparent after several generations, and communities with sufficient contact with "mobile" males for intermixing.

I insist, however, that it is not materially possible that all our ancestors coupled exogamically. We are the children of endogamy.

by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 02:18:10 PM EST
[ Parent ]
it is mine, and it is purely speculative. Well, I base it on the bit where most people do not actually look anything like their 1-6 year old selves when grown, and the fact that scent has been proven to have a heck of a lot of sway over who we find attractive. .. Actually, this theory is testable, without doing anything overly morally questionable. Just apply "scent of partners sibling" to one half of a couple and see if it murders their sex life. >,)
A positive result would also prove the original hypothetical. Somewhat .. cumbersome experimental protocol, tough.
by Thomas on Fri Nov 9th, 2012 at 02:31:31 PM EST
[ Parent ]
myth structures concerning incest

On this note, I found the critique of Freud's critique of the Westermarck effect, quoted on the Wikipedia article from a book by Steven Pinker (where I find he himself references one John Tooby) funny:

The idea that boys want to sleep with their mothers strikes most men as the silliest thing they have ever heard. Obviously, it did not seem so to Freud, who wrote that as a boy he once had an erotic reaction to watching his mother dressing. But Freud had a wet-nurse, and may not have experienced the early intimacy that would have tipped off his perceptual system that Mrs. Freud was his mother. The Westermarck theory has out-Freuded Freud.


*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Thu Nov 8th, 2012 at 12:53:34 PM EST
[ Parent ]
and ties in nicely with Michel Onfray's fisking of Freud.

I sort of wondered if it was a Jewish thing, or what. Ick.

It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II

by eurogreen on Thu Nov 8th, 2012 at 01:43:58 PM EST
[ Parent ]
I'm not sure kcurie would go along with the reference to Freud re myth structures...
by afew (afew(a in a circle)eurotrib_dot_com) on Thu Nov 8th, 2012 at 02:02:31 PM EST
[ Parent ]

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