When is it not incest?

Remove all ads!

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

 

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.

 

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.

 

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!

 

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.

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?

 

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

 

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.