Not to darken things but…. here is a piece of work about incest avoidance

What is the issue in the controversy over incest-avoidance? Can biology, psychology, or sociology settle it?

Incest avoidance has long been a debated subject in sociology due to question of whether it exists and if so how it came about, why it exists and by what mechanism is it played out? In this essay I look to highlight some psychological explanations such as the Westermarck effect and biological arguements such as avoiding genetic load. I will also try to explore where the incest taboo may have come from.
Incest in humans is defined as sexual intercourse between close relatives that is illegal in the jurisdiction in which it takes place. Inbreeding is often defined as the breeding of related individuals within an isolated or closed group of organisms or people. Incest avoidance has been defined as the tendency of organisms to avoid incest.

Since it is rare to observe in animals, historically incest was only studied in humans. It was thought that the incest taboo, compounded by religion, effectively ensured incest never occurred, but that, where it did, it resulted from societal pressures. The incest taboo is almost universal throughout the world and even in cultures with little in common. Almost all religions forbid incest to varying degrees. The idea that the incest taboo stopped incest stems from the self-regulating system of a hereditary taboo, each generation passing down the taboo so it remains indefinitely. Of course at some point the taboo has to start and one may ask why it was started. This could be because people noticed the higher levels of hereditary illness in incest born children and with or without knowing why this was the result banned incest. From this point it can be argued that with sufficiently strong enforcement people can instill a deep seated disgust from an early age such that the strength of response feels innate. This traditional view, however, started to be contested due to its inability to satisfactorily explain the behaviour of animals and why incest should seem to be acceptable in some circumstances. In RED Freud managed to popularise the view that we all wanted to have sex with our family and that the conflict of this desire with the incest taboo was a large source of psychological strife for many; more recently Socio-Biologists such as Gregory Leavitt have tried to find more universal solutions to explain incest avoidance and have looked to genetics for answers.

The idea of incest avoidance in itself is slightly flawed as the demand for incest avoidance is derived from the fact that incest imposes a genetic load. Incest’s genetic load occurs in the form of accumulations of dangerous homozygotes. These can cause debilitating diseases, can cause a lack of immunity to pathogens or may cause physical and mental deformity. If incest had no dangerous effects then incest avoidance would not exist and as such incest avoidance is just another way of maximising one’s genetic survival rate through maximising the capacity to survive of one’s children. Incest avoidance is not really the avoidance of incest for its own sake, therefore, but rather one of mate selection. In cases such as starting a new colony with a small group of individuals, incest is the best and only option and in this case it must be allowed; nature supports this arguement and so we find that incest occurs in these situations. This shows that any mechanisms behind incest avoidance are rather more nuanced than a simple rule forbidding incest.

One framework through which one may view incest is that of search cost in economics. Here we take all possible mates from the worst (A) to the best (B) and lay them along a line. A is likely to be related and b unrelated. One does not know the value of a random potential mate but may be able to narrow down the range though signals sent by the individuals. It is assumed that one knows the value of A and B and any individual they pick. A random female searches for a mate using up resources and time doing so, a cost to the individual we can call S. In doing so she finds a mate X who could be anywhere on the scale from A to B. The cost for her to look for another mate is again S. In order to determine whether she will search for another mate we take her search cost {S} and compare it to the expected gain of her searching for another mate {(B-X)/(B-A)*((B-X)/2)=(B-X)^2/2(B-A)}={the chance of getting a better mate multiplied by the expected improvement in mate}. As long as the search cost is less than (or equal to) the expected gain of finding a new mate she will search for another mate.
This framework could potentially be used to find the cost to a female of incest, by taking two individuals A and B, one related and one unrelated, and then imposing a search cost S which was adjusted until the female was ambivalent about incestuous activity. Situations where incest occurs in the wild could be checked to see whether they fit this frame. For example, where mates are limited such that both A and B are related, a female will take a related mate, as offspring that may have dangerous homozygotes are better than no offspring.

The main psychological explanation for incest/inbreeding avoidance is the Westermarck effect. Reverse sexual imprinting, or the Westermarck effect, is where people living in close domestic proximity during the first few years of their lives are desensitized to later sexual attraction. For any two given people only one needs to be in the first few years of life for the effect to take place on both (meaning the effect is pertinent to mother/son and father/daughter rape). The majority of work done on studying this effect was carried out in the Israeli kibbutz system. In this system groups of children of any given age are reared together (relation is unnecessary). A study on the marriage patterns of children from this system revealed that out of 3000 marriages across the kibbutz system only 14 were between children from the same peer group. Of those 14 none had been together during the first 6 years of life. This study was useful not only because it demonstrated the Westermarck effect in practice on a scale which would be hard to replicate but also it showed the Westermarck effects peak between birth to age 6 and its following decrease throughout childhood. This study is slightly suspect however due to the conditions of the kibbutz. Psychological studies revealed that children that grew up in the kibbutz found it harder later in life to form deep emotional attachments and as such tended to show very low marital rates (although very low divorce rates) this coupled with a high drive for uniformity may have skewed the results. The Westermarck effect has been studied in other situations such as the shim-pua marriage system, but this system again is odd in that it contains high levels of domestic abuse; as such it can be hard to extrapolate to humanity and even harder to animals. The Westermarck effect is such an attractive explanation because imprinting is a common behavior and the Westermarck effect would through a simple rule solve the problems of inbreeding, and in doing so likely incest. The likelihood of people meeting later in life having been separated at birth is small enough that in a population these occurrences would not impose significant genetic load.

One way in which the Westermarck effect can be compounded is by its absence, often cited as genetic sexual attraction or GSA. Genetic Sexual Attraction is the idea that when relatives are separated at birth and then meet later on in life they may find each other highly sexually attractive. The idea behind GSA is that people find faces similar to their own more trustworthy and likeable, and personalities etc. like their own more attractive. GSA detractors say that GSA is not congruent with other data concerning mate selection such as scent assessment. In studies based on MHC women were found to prefer men with the most dissimilar MHC which contradicts GSA. GSA is very difficult to study due to the fact that it is very rare to find situations where relations have been split only to reunite, not knowing they are related, in a way that can be studied.

It has been posited that inbreeding/incest may be controlled by a form of genetic maximisation that works to counterbalance the expected genetic load of incest. Here genetic load is taken to mean the expected difference between a society with a maximised allelic spread and an existing society. In any population one will expect a small genetic load, as people will not tend to mate with their perfect genetic partner (as defined to be the partner with whom one’s children would be expected to have the genetics which maximise the chances of survival), however this will be discounted as ‘normal’ load due to being both unavoidable in practice and negligible in effect. Incest is likely to cause a significantly higher genetic load than average and as such should be avoided. This is especially pertinent when we apply genetic load to a family as opposed to a society. If the parents have an inbuilt mechanism which causes them to try to maximise their children’s genetic buildup (working in ways such as trying to gain different immunities from both parents via sensing differing MHC’s) then they would avoid incest even though it may have small effects on a society as a whole. As genetic load is cumulative they would be even more antagonistic towards incest than one may think necessary. This can be illustrated by taking two families with different genetic propensities to incest (I assume that this process is genetically controlled because this reflex would have to be innate; society does not teach one to smell different MHCs etc.) we shall call these individuals A and B. Family A has a 1 in 2 genetic propensity to incestuous activity, Family B has a 1 in 3 propensity.

Generation 1 Generation 2 Expected Load
Family A ¼ I, ¾ NI ¼ I, ¾ NI 1/16 I-I, 6/16 I-NI, 9/16 NI-NI
Family B 1/9 I, 8/9 NI 1/9 I, 8/9 NI 1/81 I-I, 16/81 I-NI, 72/81 NI-NI

We may now attribute a genetic load a and we find that Family A after two generations has the expected load of above the normal of (a2 + 6a)/16 whereas family B would have an expected load above the normal of (a2 + 16a)/81. If we give a a value (greater than 1 to depict the increased load caused by incest) we find that there is a disproportionate link between level of propensity to incest and resulting load such that a decrease in propensity gives a larger increase in genetic load. We will give a here the value 1.5 and we find that Family A has the expected value 11.25/16 which is roughly 0.75 and Family B has the expected value 26.25/81 which is around 0.33. The ratio between these two values is 9:4 when we had a starting ratio of 3:2. We will additionally find that the more generations this is extrapolated over the exponentially greater the effect. Propensity to incest will be strongly selected against. One arguement against this evaluation is that there is a level of inbreeding or outbreeding that is optimal such that in many bird species there are high levels of cousin to cousin mating (Japanese quail). In farms inbreeding and outbreeding are balanced to achieve the optimal genes in the population. The biggest problem with any maximisation hypothesis is that it is far too complicated to be subconsciously controlled, and that it needs to be more adaptable than an innate process could be expected to be.

An arguement against genetic maximisation is that, were this to be true, individuals would only be attracted to a small part of the population based on genetics. However in nature amongst animals such as elephant seals females simply pick harem controllers instead of using scent assessment or another means of mate picking,. This implies that seals select by status and position in the community. This would surely not be a genetics based selection. What this assessment misses is that physical characteristics which earned the seal its position may be taken as an indicator of genetic build-up. This can be used to explain royal incest among humans. Hereditary Royal families are almost unique in nature as places where position in a community does not reflect one’s talents or abilities but instead lineage. As a royal, one’s fitness is artificially high and so their concern is not so much survival rates (affected by genetics) but rather keeping their family royal. One way to ensure this is incest. This can also be taken as an example of an extreme K-selected species (another example being cheetahs). In an extreme K selected species resource distribution may well be as important to the successful reproduction of one’s offspring as their genetic make-up. This may mean ensuring the father is going to invest heavily in the offspring and to ensure territory retention or resource monopolization a kin group may reproduce.

The other occurrences of incest in humans are recorded in families with extreme dominance by the father or where a daughter at an early age takes up the responsibilities of a very weakly represented/failed mother. Both of these situations are very much outside the social normal and in cases where this occurs participants tend to be aware that this situation is not desirable. In a study run on chimpanzees, the animal with a psychological setup as close to ours as possible, researchers found that under severe sociosexual deprivation, sexual disinterest including incest avoidance could apparently be overcome. However cases of this being found were very rare and female partners (the recorded cases were all instigated by two infant males) were violently opposed to the activity.

Gregory C. Leavitt is a Socio-Biologist who has looked at incest in his BOOK ……. He covered a few of the major arguements for and against incest. In one of his main arguements against human incest avoidance he argued that incest would not have been selected out in the Pleistocene. The basis of this stance was that the genetic load caused by incest would have been marginally more than that already occurring due to inbreeding due to living in small communities. One of the reasons he felt the effect of incest was overemphasized was that the weeding out effect of dangerous homozygotes was overlooked. What Leavitt seems to fail to see is that dangerous homozygotes whilst weeded out may still impart a large negative effect on the community; this could be in the form of having to be cared for when young or in pregnancy or depending on the effect of their homozygotes by passing on antagonistic but not deadly/antagonistically pleiotropic alleles.

Leavitt also drew up a list of 16 major cases in which inbreeding could be observed. He managed to show that most of these occurrences were due to either a stark lack of choices (an isolated wolf population on Isle Royale, captive rhesus macaques) or were observed in species where the chance of incest occurring is very low (i.e. species which had no need to develop a mechanism for incest avoidance as the chances of it happening are so low that negligible genetic load results due to the lack of a mechanism).

The final mechanism by which incest avoidance may be carried out is by distancing behaviours. In nature many species such as giraffes leave their group upon reaching sexual maturity and wander until they find another group. This distancing behaviour prevents inbreeding due to geographical constraints. This is observable in many different species and is seen more commonly in matriarchal societies due to the fact that the sons of matriarchs are sexually desirable but should not breed with the highest ranked female due to it being their mother. This behaviour has not been satisfactorily put down to either social cues or genetics.

With behaviours such as distancing it can difficult to ascertain whether they are driven by society or genetics. Since we have not been able to locate any control genes yet we cannot give any evidence for a genetic basis, however it seems behaviours such as distancing and scent assessment are not taught by society. This means that it is very difficult to understand why certain anti-incest behaviours exist or how they developed, or indeed whether they were even intended to be incest avoidance mechanisms.

In conclusion, incest is a lot easier to explain than the methods of its avoidance. We only find a few types of incest (isolated communities, royals, psychologically disturbed individuals) whereas there are many ways in which incest is avoided. Incest avoidance is still a grey area; it doesn’t yet seem to be describable in the universal language of genes and certainly not in the more localised capacities of psychology. The Westermarck effect appears to depict accurately an effect that would have been seemingly easy to evolve (we have evidence of many imprinting behaviours) and useful to have (anti inbreeding) but not only is it not present in many species such as ants (female iridomyrmex humilis has been demonstrated not to have any preferences between unrelated mates wherever they come from) who have incest avoidance behaviours (females will pick an unrelated mate over a related one) it is also hard to give conclusive proof among humans. Sociology and Biology on the other hand seem to be able to demonstrate incest avoidance strategies, and can suggest reasons for them, yet neither is able to prove how the mechanisms came about or what controls them. Is there an incest taboo because of genetic urges or due an understanding of genetic load and the need to prevent it? Personally I think that the taboo arose due to people voicing the views of their genes, and that many behaviours such as scent assessment, distancing and the Westermarck effect only fully make sense inside the frame of genetic control; they are innate behaviours that occur without the interference of society. This view, however, cannot be validated until genes are isolated; as such I feel that the only way the controversy over incest avoidance can be settled is by finding control genes. If this view is wrong it would lead to a lot of wasted time and so in order to fully advance the area of study I think it is important that other causes are investigated even if they are a lot messier whether psychological biological or sociological.