Wow, what a raging debate. Sorry i had to miss this last night. I had a personal emergency and couldn't get on to lit net. And what's a debate without Virgil sticking his two cents in. :D :p
There are a number of points to respond to, but so many that it will be impossible to respond to them all. First, I think Wikipedia has a very intersting entry on incest. You can read it here: http://en.wikipedia.org/wiki/Incest. But let me pull out some highlights.
Quote:
Virtually all societies have some form of incest avoidance.[1][2] The incest taboo is one of the most common of all taboos. Most modern societies have legal or social restrictions on closely consanguineous marriages.[3] Although not universal, incest constitutes a cultural taboo in most current nations and many past societies,[4] with legal penalties in some places. In some societies, like Ancient Egypt, brother–sister, father–daughter and mother–son relations were practiced.[5][6]
Which family members constitute those covered by the incest prohibition is determined by the society in which the persons live. Some societies consider it to include only those related by birth or those who live in the same household; other societies further include those related by adoption, marriage, or clan.[7]
Quote:
Some researchers hypothesize that humans have a kin recognition ability that functions in part to enable incest avoidance between close relatives, thereby protecting the gene pool of the family or tribe from excessive damage by inbreeding; and, that this kin recognition system may form a biological basis for social and psychological prohibitions against incest. [12]
Inbreeding leads to an increase in homozygosity (the same allele at the same locus on both members of a chromosome pair). This occurs because close relatives are much more likely to share the same alleles than unrelated individuals. This is especially important for recessive alleles that happen to be deleterious, which are harmless and inactive in a heterozygous pairing but, when homozygous, can cause serious developmental defects. Such offspring have a much higher chance of death before reaching the age of reproduction, leading to what biologists call inbreeding depression, a measurable decrease in fitness due to inbreeding among populations with deleterious recessives. Recessive genes, which can contain various genetic problems, appear more often in the offspring of procreative couplings whose members both have the same gene. For example, the child of persons who are both hemophiliac has a nearly 100% chance of having hemophilia.
Quote:
Psychology
Presumably because of the genetic harm done, animals inbreed only in extremely unusual circumstances: major population bottlenecks and forced artificial selection by animal husbandry. Pusey & Worf (1996) and Penn & Potts (1999) both found evidence that some species possess evolved psychological aversions to inbreeding, via kin-recognition heuristics.
Evolutionary psychologists have argued that humans should possess similar psychological mechanisms. The Westermarck effect, that children who are raised together during the first five to ten years of life have inhibited sexual desire toward one another, is one strong piece of evidence in favor of this. In what is now a key study of the Westermarck hypothesis, anthropologist Melford E. Spiro demonstrated that inbreeding aversion between siblings is predictably linked to co-residency. In a cohort study of children raised communally (as if siblings) in the Kiryat Yedidim kibbutz in the 1950s, Spiro found practically no intermarriage between his subjects as adults, despite positive pressure from parents and community. The social experience of having grown up as brothers and sisters created an incest aversion, even though the children were genetically unrelated.
Further studies have supported the hypothesis that some psychological mechanisms cause children who grow up together to lack sexual attraction to one another. Spiro's study is corroborated by Fox (1962), who found similar results in Israeli kibbutzim. Wolf and Huang (1980) reported similar aversions in Taiwanese "child marriages", in which the future wife was brought into the family and raised with her fiancé. Such marriages were notoriously difficult to consummate and led to decreased fertility of the marriage. Lieberman et al. (2003) found that childhood co-residency with an opposite-sex sibling (biologically related or not) was significantly correlated with moral repugnance toward third-party sibling incest.[12]
Quote:
Laws against adult incest are sometimes questioned on the grounds that such relations do not harm other people and so should not be criminalized. Some legal systems no longer criminalize adult incest. The French Criminal Code removed its incest prohibition long ago, and other countries such as Belgium, the Netherlands, Luxembourg, Italy, Portugal, Turkey, Japan, Israel, Argentina, Brazil as well as a few other Latin American countries and several U.S. states have followed suit. In most countries where the crime of adult incest has been abolished, acts of incest involving a minor are still punishable.
From time to time proposals have been made for the repeal of incest laws, for example, the proposal in Australia by the Model Criminal Code Officer's Committee in the November 1996 discussion paper "Sexual Offences against the Person". This particular proposal was later withdrawn by the Committee due to a large public outcry. Defenders of the proposal argue, however, that the outcry was mostly based on the mistaken belief that the committee was intending to legalize sexual relations between parents and their minor children.
One thing to keep in mind is that the wiki entry conflates all types of incest into a general term, while we are particularly speaking of sibling incest, even something less dubuious as cousin incest. For me, the key paragragh is the one on psychology which I'll requote here:
Quote:
Evolutionary psychologists have argued that humans should possess similar psychological mechanisms. The Westermarck effect, that children who are raised together during the first five to ten years of life have inhibited sexual desire toward one another, is one strong piece of evidence in favor of this. In what is now a key study of the Westermarck hypothesis, anthropologist Melford E. Spiro demonstrated that inbreeding aversion between siblings is predictably linked to co-residency. In a cohort study of children raised communally (as if siblings) in the Kiryat Yedidim kibbutz in the 1950s, Spiro found practically no intermarriage between his subjects as adults, despite positive pressure from parents and community. The social experience of having grown up as brothers and sisters created an incest aversion, even though the children were genetically unrelated.
The basis of my argument rests on this: that brother/sister love is fundementally different than romantic love and to cross the two would be a perversion that would have essentially destroy the family unit and therefore undermine society. Now, you can pull that apart and say what consititutes the family as the basic social unit, but centuries of cultural formation has built it and to destroy it would be chaos. Moral laws are by nature evolved to sustain society. And people are civilized to establish moral boundaries. Civilization equates to moral boundaries. Something like sibling incest requires a moral boundary.
As to the specific case, I still doubt that these adults had no notion that siblings could not do this. They are using it as an excuse to get out of criminal prosecution. Two years does strike me as a harsh penalty for this, but then again I'm not sure what the right penalty is. Certainly changing the marriage laws to accomodate this perversion :p is out of the question.