Some case studies on inbreeding

Kibbutz study

So the Kibbutz study in question was supposed to show, in Israeli groups of children raised together communally, that mere close proximity in those formative years was enough to trigger the incest avoidance mechanism, and cancel or invert any sexual feeling between such young people as if they were relatives. For more on this and the debunking, I suggest Instinctive Incest Avoidance: A Paradigm Case for Evolutionary Psychology Evaporates from Justin Lieber, but the abstract should do just fine:

One example is based on Joseph Shleper’s description of some Israeli kibbutzim collective farms, which raised children communally, so that coincidentally the Westermarck effect could be supposed to apply to the entire cohort of children, who did seem not to engage in lustful sexual activity with each other, nor, much more certainly, marry (the small number of exceptions were supposedly cases where one or the other joined the kibbutz after their sixth birthday.
But Shleper described 1960s kibbutzim, which though Shleper denies and ignores this, strongly cultivated and systematically enforced a no privacy and no-sex-before-marriage atmosphere, which the youngsters only escaped when they all entered compulsory military service in their late teens, when they had their first opportunities for dating and courtship, although even then under strong parental and communal pressure to marry members, not of their own, but of nearby kibbutzim (which was, shades of Levi-Strauss, intended to strengthen the ties between the kibbutzim communities). […] Moreover, re-examination of Shlepher’s data suggest serious gaps between Shleper’s interpretation and the data. In any case, several marriages did occur unnoticed by Shleper that violated his claim that “not a single case of intra-peer group marriage occurred”.

Despite common features, not all kibbutz movements were the same and some were relatively more conservative about youth sexual matters, some maintaining sleeping arrangements and shower arrangements to avoid temptations until a later age. Shepher’s statement was directly opposed by numerous studies, pointing at the fact that indeed social scripts in many kibbutzim, rejected the idea of romantic or sexual relations between co-reared peers.
Leavitt argued that according to Shepherd himself, children of the same peer group engaged in intense sexual play with one another until the age of 9 or 10, which was inconsistent with the theory of negative imprinting and sexual aversion.

Shor and simchai (in a study of Asian « minor marriages », involving adopting a young child bride before marrying her) found that a number of sociocultural factors were important in explaining differences in attraction levels and romantic/sexual relationships avoidance. Most important among these factor was social cohesion and fears of hurting the integrity of the group. Other factors reported as important in preventing romantic and sexual relationships were age homologs and the general atmosphere in the kibbutzim, often reported to be intolerant of over sexuality in general and of romantic and sexual relations withing the peer group in particular.

Importantly they also controlled for those who had indeed passed their full youth reared together, while it is true that a part of kibbutzim youth now have had significant time spent with their families, hence theoretically lessing peer negative sexual imprinting.

According to them, the sample controlled for this variable, on average showed attraction toward co-reared peers in later years and almost none of them developed feelings of sexual aversion.

That suffices to show the lack of honesty of those scientific researches. But at least they did not outright fake the data, that much should be commended I suppose.

A Canadian study showing no aversion, but merely restraint in coitus in particular

In A test of the revised Westermarck theory Irene Bevc and Irwin Silverman), 170 subjects related their experiences while having been separated (then subsequently reunited) from their sibling (of opposite sex) during early childhood.

Respondents reporting potentially procreative, post-childhood sexual acts (attempted or completed genital intercourse) with siblings were compared with those reporting sexual relationships excluding procreative acts, and a third sample reporting no post-childhood sibling sexual behavior. Consonant with expectations from the earlier study, prolonged separation during early childhood was associated with procreative post-childhood sexual activity but not with other post-childhood sexual activity. Contrary to predictions, however, both sexual activity groups reported significantly more nudity and physical contact with siblings during childhood than subjects reporting no sexual activity.

Interestingly, this seems to advocate for an instinctive separation of the two kinds of sexual activities - as detailed by Mr Burger - and the understanding of incest as primarily energy-based, while sometimes - when necessary or adequate, socially, ecologically and spiritually - feeding the reproductive program.
In any case… No aversion or overall negative feelings.

General documentation

For information, instead of skimming through the entire damn literature like I had to a reader should instead pursue the aforementioned studies, available online through which any intelligent person should know how to handle:

  • A test of the revised Westermarck theory, Irene Bevc and Irwin Silverman
  • Instinctive Incest Avoidance: A Paradigm Case for Evolutionary Psychology Evaporates, Justin Lieber
    Plus a few others:
  • the seminal Disappearance of the Incest Taboo: a Cross-cultural test of General Evolutionary Hypotheses from Leavitt taking account a broad study of the incest question in 121 societies. Though we do not agree on purely materialistic explanations, it is interesting to see how in general, contrary to common sense in what we call primitive societies, first degree incest was actually not the most vilified degree, as it wasn’t socially the most disruptive regards to the Alliance theory - Tylor vs. Westermarck: Explaining the Incest Taboo, Gregory Leavitt
  • Thornhill, N. (1991). An evolutionary analysis of rules regulating human inbreeding and marriage

Those studies demonstrate the absolute lack of generality in human societies regarding to that taboo. That alone is enough to invalidate in one fell swoop, the totality of all neo-darwinian/sociobiologist arguments.