Taking a religious point of view, we are all sons and daughters of Adam and Eve. So therefore any relationship we have with another human is incestual in nature. Now obviously if that's the case the word 'incest' really has no meaning.

But ignoring that, when is a relationship with a member of your blood related family not incest? How many generations need to pass before the offspring can create their own?

Sadly I can't draw a family tree here but we'll take an example of a married couple called Bob and Sarah and they have two children called Jacj and Jill, those children marry other people and they have two children, those children marry... and so forth. When can the great-great-etc.etc. grandchildren have a sexual relationship with each other? How far 'diluted' must they be from their origional parents?

Every generation the blood of Bob and Sarah is halved in the children. What amount of similar blood is 'allowed'? Obviously Bob and Sarah's immediate children will have 100% blood (or 1/1) of their parents whereas Bob and Sarah's grandchildren will have 50% or 1/2 blood ties to their grandparents and therefore 50% relation to their cousins. The next (3rd) generation would be 1/4. The 4th generation would be 1/8.

Obviously they can't just have a relationship with their immediate cousin. For this to work they would have to have a relationship with their opposite on the other side of the family tree. Say the 4th grandchild of Jack could have a sexual relationship with the 4th grandchild of Jill. Remember Jack and Jill are both the children of Bob and Sarah.

From a non religious point of view: It would depend on how many "bad traits" are carryied by the family line and just how bad they are. First cousins seems to be to close, many of my 14 grandchildren (smiles with pride, best kids in the world) look and act too much alike to not be carrying a lot of what could be trouble. Second cousins seems to be about as close as is safe and that is also what the laws are in most states AFAIK but I could be out of date about the law.

Fourteen... bloody 'ell. Don't be telling my mother or she'll want me to catch up... being only child and all, gah!

??? Just got knocked off trying to post.
I tell my kids since I stopped with 3 I am the smartest one in the bunch. Stop when the parents get outnumbered!

Lol, Old one, your children must be nuts. :)

Incest is actually a bit more complex than that, depending on what society you take it from. Some say anyone raised in the same household, regardless of blood relatives or not. This means marrying your sister is fine if she was raised by the neighbors. Others are more like the standard today, but say relation by marriage or adoption is just as bad as by blood, so the brother of a now deceased husband can't marry the widow, nor can two children who were both adopted (from seperate families) by the same parents.

As for blood relations, second cousin seems to be the modern standard, but I doubt many would claim more than 1/16, and all human beings is rediculous. There must be a 'close family relation' and stretching that to a whole species which is ~150K years old and spans the entire planet is insane. You might as well say we're all 'close family relations' of cockroaches and black mambas at that point.

To clarify. A Second Cousin then would be for example your parents's parents's sibling's child's child? Therefore having 1/4 similar blood ties to each other.

I forget whether the threshold is 3rd or 4th cousins (5 or 6 generations). I think 5 Generations from the common ancestors is fair game.

@Abomination: To tired to figure yours out. Try this Someones grandchildren are 1st and their kids are 2nd so..great grandkids. I think in my muddled way we said the same thing?? Pretty far removed. Yes my little ones who are all but the girl much bigger then I am are a wee bit touched sometimes, get it from me :-D

First cousins are fine from a genetic point of view. The genes are sufficintly "diluted" for there not being higher risks than with any other couplings. In Sweden and I think in most countries first cousins can marry and such. It is mostly a social stigma and even as that a fairly recent one. Pretty sure that through history cousins marrying have been quite common.

From a personal view there is quite a large difference between screwing the cousin you spent your entire childhood with and the cousin you met twice before accidentely bumping into a hot chick on hte dancefloor and bring her home just to find out afterwards that it was your cousin you only met twice before.

If you count being allowed to marry as an indication of incest, then in England this includes:

Grandparents
Parents
Parents Siblings (Uncles, Aunts)
Parents half-siblings
Adoptive Parents
Siblings
Half-Siblings
Children
Adopted Children
Siblings Children (Nieces, Nephews)
Half-Siblings Children
Grand Children

In Scotland, Great grand-parents/grand-children are added to the list.

So having sex with your Cousin doesn't count as incest in the UK.

Wow, I hold a belief that 3rd Cousins would be pushing it. I mean I have several female cousins, all rather attractive, but the idea of 'having it off' with them disgusts me. I mean my mother and their mother share identical blood so my cousin's blood is 50% the same to my own...

I thought there were numerous reports that the children of first cousins were often deformed.

I was dead worried some time because I have a cousin who is fit as ****. If I didn't know who she was, I'd proper knock her hips out. Cousins aren't technically incest, but it is a bit... dodgy, pml.

@Abom:

I can't say I disagree with your feelings, although from a personal standpoint it's irrelevant.
Genetics are not quite as simple as your percentages either -

Monozygotic (MZ, identical) twins share 100 percent of their genes, while dizogotic (DZ, fraternal) twins share only 50 percent of their genes (the same percentage as non-twin siblings). So unless your Mother and Aunt are identical twins and then married identical brothers (Which would be 50%), your "sameness" to your cousins is probably about 12.5%

The risks don't appear to be massively increased. From the NHS (UK National Health Service):

The population risk of having a child with a severe or lethal medical condition is around 2%; for a first cousin couple this increases to around 5% It particularly increases in families with a history of consanguineous marriage. (Second cousins or closer).

It's also worth remembering that we're all 99.9% the same anyway, and there's more genetic diversity in your average tribe of chimps than in the entirety of the human race.

From a non religious point of view: It would depend on how many "bad traits" are carryied by the family line and just how bad they are.From a religious point of view, it would be quite bad to disregard the genetic problems, as well. At least depends what religion and what point of view it is, but I wouldn't really be able to reconcile my religion with the idea of not giving a thought to what kind of stuff my kids are about to be born with. ;)

There are two problems with incest: 1) genetics, 2) family relations.

For both of the reasons above, sexual relations between ascendants and descendants are particularly freaky. Between siblings, it also has to feel weird. As for further degrees of kinship, it depends on the culture, I guess, especially the social customs and the living circumstances. For example, it would be much freakier to go out with cousins if all the offspring of the given patriarch lived in the same place. The fact that siblings are off limits gives certain opportunities and keeps certain things straight that could otherwise go bad.

If anyone is interested, in most jurisdictions there's a marriage ban between ascendants and descendants, siblings and often also aunts or uncles and nephews or nieces, maybe even first cousins.

In the Catholic canon law (link (http://www.vatican.va/archive/ENG1104/__P3Y.HTM)), as a rule, you can't marry up to fourth degree collateral line (roughly translates as four births between you and the other person, it not being an ascendant-descendant kinship). You can receive dispensation up to 3rd degree (means you can't marry yourself or your siblings, but aunts and uncles or nephews and nieces are a different story). Suffice to say I don't really like the way certain people already know they are related before they marry and then they make some fuss and actually get the marriage declared null (the marriage once contracted can't be declared null for reasons of consanguinity unless any degree of direct line or 2nd degree collateral line, if consent persists in both parties).

To build on what Carcaroth is saying, brothers and sisters are not 100% identical, unless we're talking about identical twins. They are (regardless of gender) 50% genetically similar.

So when we're talking about 1st cousins, that's what the relationship would be if one of my brothers and I have children. Our wives aren't related in any way. Therefore, since my brother and I share 50% of the same DNA, our children will posess 25% of the same DNA relative to each other. With 2nd cousins, it drops to 12.5%, and 3rd cousins 6.25%.

With a nod to Chevalier who I tend to agree with my opinion as to second cousins being the closest anyone should consider chancing kids with stands. The first cousin risk of more than doubling lethal conditions is just too much.

Chinese aren't supposed to marry people with the same family name, since they would be considered brothers/sisters in a sense (and to prevent inbreeding/incest in every generation).
For example, my family name is Wong, and I can't marry another Wong (but only if the person's family name has the same meaning, since there are more than one word in Chinese pronounced as Wong).

Kinda flawed actually, since a girl would have to change her family name when she marries out of the family and her children would have the father's family name instead.

How much it is adhered to depends on the society I suppose, but my parents are still pretty much against such marriages. I guess even now, its still frowned upon.

I'd say at least second cousin, and you must also be unaware of your blood relationship with the other person.

For example, in my school, there is a girl who I suspect is the grandchild of my grandfather's brother. She has the exact same last name, and to make it even more freakier, she has the same first name as my sister. Needless to say (?), I avoid even looking her way.

I understand genetically the non-identical twins wouldn't be genetically identical, but to say they're 50% is also incorrect since there are so many genetic combinations possible between the two. It's not a matter of just X and Y, there is the eye and hair color, bone structure, facial features, height etc. and your sibling won't have brown eyes BECAUSE you have blue eyes. It is entirely possible for your year younger sibling to have identical DNA to you, however the PROBABILITY is low.

I was using blood-ties since it's the only thing one can be 100% sure about the division. I know it doesn't have much scientific backing but it sure as hell has some social backing.

I understand genetically the non-identical twins wouldn't be genetically identical, but to say they're 50% is also incorrect since there are so many genetic combinations possible between the two. No, it's absolutely correct that it's 50% genetically identical between siblings. If you have 10 brothers and 10 sisters, you will share 50% of your DNA between all of them, and all of them will share 50% of their DNA with each other. I have two brothers. 50% of my DNA is the same as theirs, and 50% of their DNA between them is also in common. You're correct that gender has nothing to do with it.

It is because of the very thing you mention that this is true - there are literally billions of genes that are passed on by each parent, and for each gene, you have a 50-50 chance of getting either of the two genes that each parent possesses. It's just like flipping a coin two billion times. Maybe you won't get exactly 1 billion heads and one billion tails, but with a sample size that large, you will still approximate a 50-50 distribution. Siblings are 50% genetically identical, even though in reality you may only be 49.9999% identical or as much as 50.0001% identical - that's still 50-50 for all practical purposes.

So does this mean that the children of close siblings are only 75% human? :D

Wordplay actually brings up an interesting topic, albeit in a roundabout way. If siblings had children, they would be 75% genetically identical, moreso than the parents even - strange indeed.

Here's another strange real life example from my own family. And it also ties in a little bit to the topic of this thread. My wife has both full siblings and half siblings - kind of. As has been previously stated, all full siblings are 50% genetically similar. Half siblings are normally 25% genetically similar, as they have one parent in common.

My wife's father married and his first wife died during the birth of their second child. My wife's father later remarried, but the odd thing about this is that he married his first wife's sister. Since the sister was 50% genetically similar to his first wife, the children of the second marriage were 37.5% genetically similar to the children of the first marriage. So they are kind of like 3/4 siblings. I'd like to point out that since my wife's father was not in any way geneteically related to his first wife that this does not represent incest.

I think odd was the right word, Aldeth. Personally, I have as little to do with most members of my family as possilbe -- so any relationship is a little too close for me (after all, I'd then have to deal with even MORE of my family).

Incest is really driven by culture. Jerry Lee Lewis married his 'second cousin, twice removed' (I can never keep track of what those things mean) -- and it would have been okay in the public eye had she not been 13.

I read a book while taking cultural anthropology about a small tribe in South America (To Hunt in Morning was the title). For them, it was really necessary to engage in what most of the world would consider incest. They also had their taboos:

mother's - sister's - child -- taboo
father's - sister's - child -- okay
father's - brother's - child -- taboo
mother's - brother's - child -- okay

This is called a parallel cousin taboo and is quite common.

I was suprised to find out that first cousin marriage is legal in 21 states in the US. What's even more surprising is that Kentucky is not one of those states.

Wow, I hold a belief that 3rd Cousins would be pushing it. I mean I have several female cousins, all rather attractive, but the idea of 'having it off' with them disgusts me. I mean my mother and their mother share identical blood so my cousin's blood is 50% the same to my own...
About the DNA, thats where most people are wrong. Infact a child is not made of 50% ads 50% mothers. Its made of roughly 16%dads and 16%mothers, the rest being roughly the same for all humans, with it ofcause being affected by ancesters, but thats why its roughly the same.

So when you get it off, as you put it with a cousin, you only share roughly 16% and its very rough here and can variate a fair bit. often its a lot less, since its no way sure that brothers and sisters share 100% same dna, and its even less certain that cousins inherit the same 16%. But the risk for deformed children is higher when you run it so close as first cousins, especially if it takes place over several generations.

[ October 10, 2006, 22:59: Message edited by: Equester ]

Albert Einstein divorced his wife to marry his cousin...and he was a genius.

Actually, if you want to get into DNA, you should do it case by case. It is possible, though not likely, for a brother and sister to have entirely different DNA. The child gets half the DNA from each parent, so if child 1 gets half A and child be gets everything that isn't in half A, lets call it half B, then they don't share any more with each other than they would with a total stranger.

On the other hand, they could have identical DNA, even without being twins. The odds of either of these are incredibly long, but it is possible, and cousins are even more likely to have different DNA. Remember, we're talking about probabilities here, not guarantees.

Albert Einstein divorced his wife to marry his cousin...and he was a genius.He did, but did he ever bed her?

The biggest thing against marrying my cousins is teh fact that I know about the in-laws already, and that scared the hell out of me!

He did, but did he ever bed her?I'd say that is very probable, if he married her. ;)

The child gets half the DNA from each parent, so if child 1 gets half A and child be gets everything that isn't in half A, lets call it half B, then they don't share any more with each other than they would with a total stranger. On the other hand, they could have identical DNA, even without being twins.In practice it is impossible for that to happen due to a process called recombination, which I will explain in more detail below. If there were no such thing as recombination, it would be theoretically possible for what you described to actually happen. Humans have 23 pairs of chromosomes and each parent donates one of their pair (so either Chromosome A or B) so that the child also has one pair of each. So in theory a parent could donate all 23 As to one child and all 23 Bs to the next child, meaning their DNA would be completely distinct. Conversely they could donate all As and all As again, which would result in complete similarity. The odds of that happening are 2^23.

However, recombination prevents this from ever happening. In the process of making egg and sperm cells, all the chromosomes undergo a process called recombination, in which genetic material is exchanged between chromosomes. To explain this by example, lets say a person has one gene for brown eyes and one gene for blue eyes. The brown gene is on Chromosome A, and blue gene is on Chromosome B. Through recombination, you could reverse that and have the brown gene now on Chromosome B, and the blue gene on Chromosome A. However, each Chromosome codes for dozens of traits, and all of the other traits that chromosome A coded for remain on A, and all of the traits chromosome B code for remain on B. In other words, the chromosomes are exactly the same except for the trait regarding eye color. The recombinative process is completely random. It can occur multiple times between two chromosomes during the formation of sex cells, or not happen at all. And that possibility exists for all 23 chromosomes.

So, while the mathematical answer to how many combinations of traits you can pass on is 2^23, recombination pushes that number a great many orders of magnitude higher. The number certainly isn't infinite, but I wouldn't even want to guess at the number of potential combinations. Let's put it this way. A man produces several million sperm cells every day, from the time he hits puberty until the time he dies. Over the course of his lifetime, the odds state that no two sperm cells will ever be exactly the same.

And this is why I must say again, that regardless of the genders involved, brothers and sisters share 50% of the same DNA, with a variance of only 0.0001%. It's not possible to be exactly the same (except identical twins), and it's not possible to be entirely different. It's not even possible to be 49% or 51% similar. The range is 49.9999% - 50.0001%. This number is the same whether the parents involved have 2 children ot 2 million children. All of them will share 50% of the same DNA when compaing them with each other. Obviously, there is variation regarding which 50% of the DNA is in common, but in all cases there is 50% in common, and 50% different.

I didn't know all that, and it is very interesting, although in a strictly theoretical sense, you've already stated that it isn't impossible, unless I misunderstood something. You stated that it is possible that recombination doesn't happen at all for a particular chromosome, and I'm assuming that, given increadibly high odds, it is possible that it could not happen for all chromosomes being donated by both parents twice, which could result in two identical children or two totally different children. If I'm wrong in that assumption, please tell me. Also realize that this is a strictly theoretical analysis and I would be suprised if it happened even once in all of human history, given the numbers you're suggesting.

Speaking complete theoretically, I suppose there is something approaching an infinitely remote chance of this occuring. While recombination has not been shown to occur all the time in all chromosomes, and not at the same rate in all chromosomes, I've never read a single report about recombination not occuring in any chromosomes during sex cell formation. Common numbers cited for recombinative processes usually number in the thousands for each individual sex cell, so it's truly a rarity for the number of recombinative processes to even number under 100, much less zero.

The biggest factor in the number of recombinations that take place on each individual chromosome pair is the size of the chromosomes. The pairs of chromosomes are numbered 1 through 23, with pair one being the largest, and pair 22 being the smallest (the 23rd pair are the X-Y sex chromosomes). Simply put, the bigger the chromsome, the more chances it has to recombine.

Also realize that this is a strictly theoretical analysis and I would be suprised if it happened even once in all of human history, given the numbers you're suggesting. The numbers I'm suggesting put the odds beyond the total number of people who have ever walked the earth. Just to give you an idea of what we're talking about. The odds of producing two genetically identical children are the same as producing two genetically distinct children, so what I say for one goes for the other.

The odds of a woman donating all the same chromosomes twice are 1 in 2^23. The same goes for the man's chromosomes. So the odds of getting both to happen at the same time are 2^46. That alone makes the odds extremely long. However, you then have to factor in at least hundreds if not thousands of potential recombinative processes that may occur. Keep in mind that recombination is a random event, and that it can occur anywhere on the chromosome. Since the idea of no recombination taking place seems impossible even in the theoretical sense, we are then left with the possibility of the same sets of recombinations taking place in two separate instances in which the appropriate chromosomes were also donated both times. The mind boggles at what the odds of that occuring would be.

So to answer your question, given an infinite population set, I suppose it could be theoretically possible to have this happen. Then again, infinite population sets don't exist in reality, so this can only exist in a theoretical, non-realistic scenario. The current human population of 6.7 billion people isn't even approaching the number needed to hope to see something like that happen. The odds of both parents donating the same sets of chromosomes twice are over 70 trillion to one. As if that wasn't bad enough, the odds of getting the same set of chromosomes twice are much, much, much better than the odds of getting identical recombinations of occuring.

All I can tell you is that there have been extensive DNA testing done within families, and siblings have consistently been in the very small range of 49.9999% and 50.0001 percent genetically similar. We've never even seen a 51% or a 49% which is why I'm hesitant to even think of a 100% or 0% as a theoretical possibility.

*eyes glaze over* So can I bang my cousins or not? :p

If you must, promise me two things:

1: You'll wear a condom just in case.

2: I don't need to hear about it...

See no evil, talk no evil, speak no evil.

That's the motto if you intend to marry a relative.

My grand parents were first cousins.

They got married a little over 60 years ago in a small "back country" village in Quebec, Canada. This is relevant as context.
The Catholic Church was very influential during that time, my grand parents were from very religious family.
My grand father had to get a special "permission" from the Diocese.
He had to travel 2 days and pay 10$ (that represent about 1 month savings for him back then) to get the permission.

All his great children knows this story because he loved to tell it all the time. He was obviously very proud of it.

Personally, I would certainly not feel right having any kind of relationship with any of my cousins. We are just too "close" (like brother/sisters) for that.

Sorry - Off Topic
What a surprise, the Catholic Church charging to give someone permission to Marry. A months savings is absolutely diabolical, how did they justify it?

My cousins are ugly and they are either too young or too old for me :p :lol:

Actually, even if it is scientifically safe, at what point is it socially taboo for them to marry/screw?

Different places different taboos. We have jokes in this area about people seeing exwives at family reunions. I have never actually seen this but every large extended family has "cousins" of some degree in most or all of the others. Small isolated town. In So Cal where I was raised that would have caused a Eweeew kinda reaction and comments about Special K Kids. That area had solid settlement from the coast in LA to the far side of San Berdo, about 50+ miles. Lots of people to select from. Still think consensus seems to be at least 2nd cousins.

We have jokes in this area about people seeing exwives at family reunions.If you've been married three times and have the same Inlaws, you might be a Redneck...

I think in Bulgaria the church prohibits it up to third cousins (I think including). I'm not sure what the official law is but generally I'd avoid flirting with my cousins, unless all other options are exhausted... In which case, Abomination, check the law first. I'm pretty sure in Australia it was a punishable offense, though I have no idea about NZ.

This was very interesting, by the way: http://en.wikipedia.org/wiki/Image:Map_of_USA_with_Incest_Legality.svg

What's even more surprising is that Kentucky is not one of those states. Was that really necessary. :shame:

Siblings are able carry substantially more (or less) than 50% of the same genetic material. In reproduction, I will pass only half of each of my 22 trait-affecting chromosome pairs on to my offspring (I did before my vasectomy, at least). My wife will do the same. Since I always pass on half of my genetic material, I will always share 50% of my genetic material with my children (unless the coupling was incestual....in which I would likely share substantially more than 50% with them**).

Since my wife and I only pass on one half of each chromosome pair, it is technically possible (but really unlikely)that we could have 2 children who, while they share 50% of the same genetic material with each of us, share absolutely no genetic material with each other (meaning that neither my wife nor I passed the same chromosome twice). It's also possible that the children would share exactly the same genetic material (meaning my wife and I each passed the exact same 22 chromosomes we passed to the first child along to our second child). Bottom line......siblings probably carry 50% of the same genetic material.....but it isn't absolute. A father or mother, however, will always share 50% of his or her genetic material with each of his or her children (unless incest or genetic mutation are muddying up the waters, of course). A father or mother will then share 25% with grandchildren, 12.5% with great-grandchildren, 6.25% with great-great-grandchildren, etc (unless incest or genetic mutations step in, of course).

** To the best of my knowledge, my wife and I will never be invited to the same family reunion.

[ October 28, 2006, 08:09: Message edited by: Drew ]

Read Aldeths post above. Technically possible, yes, but verging on the impossible.