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Old 12-06-2018, 04:32 AM
Velocity Velocity is offline
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How much "genetic distance" is needed for inbreeding to not be a problem?

Not a need answer fast.

With incestuous inbreeding, the children that are born are vulnerable to genetic disorders passed down because the family genes are too close. From a scientific standpoint, just how much diversity/difference is required for this problem to not be present? If two distant cousins bear children together, is that enough mixed diversity to avoid inbred issues, (and how far distant exactly?)
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Old 12-06-2018, 05:32 AM
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With incestuous inbreeding, the children that are born are vulnerable to genetic disorders passed down because the family genes are too close.
Genetic diseases can inherited even if there is no shared heritage between the parents.

Genetics is a probability thing. Brother/sister share on average 50% of their DNA. There is no degree of diversity that guarantees a genetic disorder (expressed or recessive) in one parent will not be present (either expressed or recessive) in their progeny.

Once the relationship is 3rd cousin then the average shared genes of 0.78% is not significantly different to that existing in the general population.
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Old 12-06-2018, 06:13 AM
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Depends on how cute he/she is
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Old 12-06-2018, 07:03 AM
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The master speaks :

https://www.straightdope.com/columns...sins-marrying/

"A recent review (Bennett et al, Journal of Genetic Counseling, 2002) says that, on average, offspring of first-cousin unions have a 2 to 3 percent greater risk of birth defects than the general population, and a little over 4 percent greater risk of early death."
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Old 12-06-2018, 07:33 AM
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I suggest you look at the data in Table III, etc. in this paper (PDF).

Note that when you read something like "an increase of 2-3% of birth defects" when already there's a 2-3% chance of such birth defects means a doubling of the odds of something bad happening.

And that's with one-off unions. After a few generations of cousin marriage things get much worse. While a 3rd-cousin marriage is fairly safe, this should be a one-time deal. No repeats over each generation.
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Old 12-06-2018, 08:27 AM
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Genetics is a probability thing. Brother/sister share on average 50% of their DNA.
As Mr. thule implied in his full post, inbreeding is a matter of probability. Two parents who are almost unrelated might give their child a bad homozygous allele pair by bad luck; while an incestuous couple might "get lucky" and produce a healthy child.

Note that the chance that the offspring of a brother-sister mating inherits two copies of a particular rare allele is 0.25 (= 50% x 50%). This is the "Wright's Inbreeding Coefficent" (WIC).

Animal breeders (dogs, etc.) will often maintain pedigrees and calculate the WIC for various proposed matings. However there is no clear answer to how high a WIC can be and still be acceptable. Some webpages imply that even 0.01 is too high (are they "protecting themselves"?), but some breeders will want a high WIC because they seek an especially "pure" breed. One common rule of thumb, I think, is that WIC shouldn't exceed 0.05.

A first-cousin mating gives WIC=0.0625 if the ancestors are all otherwise unrelated to each other. It will be somewhat higher if several of the ancestors were themselves the results of cousin marriages. Double first-cousin mating and uncle-niece mating each have WIC=.125, which is certainly beyond the threshold of prudent risk.

At least three Kings of Spain had WICs in excess of 0.20 according to their official pedigrees. These include Carlos II 'el Hechizado' who had severe deformities; his grandfather Philip III; and the Bourbon King Alphonso XII. (Alphonso, however, is not cnsidered to be the product of inbreeding: despite the official pedigree it is generally accepted that his natural father was one of his mother's several lovers.)
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Old 12-06-2018, 09:20 AM
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Note that when you read something like "an increase of 2-3% of birth defects" when already there's a 2-3% chance of such birth defects means a doubling of the odds of something bad happening.
But that's different from "a 2 to 3 percent greater risk". At least, if everyone involved is using the terminology consistently and correctly, which you probably don't want to take for granted.
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Old 12-06-2018, 09:52 AM
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I wonder - the original Easter Islanders were probably a single flotilla - one or two canoe-loads? This on top of a chain of expansion that meant the genetic diversity must have already been getting poorer and poorer as settlers moved east from island to island. Of course, these were big canoe-loads, so maybe 100 or more people? yet there do not appear to have been such problems in the Easter Island population that is believed to have peaked about 15,000.

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Old 12-06-2018, 10:37 AM
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Genetic relatedness decreases with the inverse square law, and even first cousin marriages were quite common in the US before 1900.

While I am definitely of the modern mindset that cousin marriage is wrong, the risk of a 40 year old women having a child with a genetic disorder is higher than first cousins.

Remember the risk is with recessive genetic disorders. The minimum viable population is really about risk, and with ~100-200 individuals you could, with management, repopulate the world. Lower numbers are higher risk, and at higher risk of divergence genetically but it is possible.

Also remember that in some time in the past 100,000 years there was only about 1000 humans or less worldwide for a very long time.

Now with easy movement and communication the risks aren't worth it but we actually have real world examples with other species rebuilding with 20 individuals without controlled breeding programs. But the risk of going extinct due to a recessive genetic trait go way up with numbers that small.

Had the original settlers of Easter Island arrived with a large number of significant recessive genetic traits they would probably have gone extinct too.

Note that even at the time of Charlemagne to someone who is directly related today, the modern person will have 4,000,000,000,000 direct great-grandparents at that level, which is about 70,000% more individuals than existed in Europe at the time. So the very minor differences that are made up among all populations in Europe is mostly due to inbreeding.

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Old 12-06-2018, 11:21 AM
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Genetic relatedness decreases with the inverse square law...
What two things are related by the inverse square law, exactly?

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Also remember that in some time in the past 100,000 years there was only about 1000 humans or less worldwide for a very long time.
This is a bit of an exaggeration - there's no evidence for this severe a reduction for a long time. It's true that modern human genetic diversity corresponds to a surprisingly low effective population size of the order of 10,000. But even a brief population crash wipes out genetic diversity for a long time (diversity goes with the harmonic mean). Numerous models have been proposed to explain the low diversity, including multiple bottlenecks or a somewhat larger (but still small) population for a longer time; there's no conclusive evidence about which is correct.
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Old 12-06-2018, 11:34 AM
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I wonder - the original Easter Islanders were probably a single flotilla - one or two canoe-loads? This on top of a chain of expansion that meant the genetic diversity must have already been getting poorer and poorer as settlers moved east from island to island. Of course, these were big canoe-loads, so maybe 100 or more people? yet there do not appear to have been such problems in the Easter Island population that is believed to have peaked about 15,000.
Lack of genetic diversity (which reduces the pace at which continued evolution can proceed) and inbreeding are slightly different issues. Note that individuals with bad homozygous genes may be unable to reproduce, so the gene pool will gradually improve. (IIRC, a population which starts with N unrelated individuals will tend over time to a WIC of 1/N if breeding is even.)

Pitcairn Island had a very small number of initial breeders. Has there been a study of the birth defect rate there?

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Also remember that in some time in the past 100,000 years there was only about 1000 humans or less worldwide for a very long time.
Do you have a cite for this? I thought there was some controversy here, and do not recall the "for a very long time" part.
("Ninja'ed" by Riemann.)
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Old 12-06-2018, 11:59 AM
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To clarify I was not referencing the Toba theory, which is disproved.

I will not be able to provide cites until tonight, but this is related to diversity studies of other great apes etc...not the Toba catastrophe theory.
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Old 12-06-2018, 12:11 PM
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Tangential, but I'm interested in talking bottlenecks, here.

So say there WAS a bottleneck. 10,000 humans 100,000 years ago - or whatever the hypothesis is - all on the edge of extinction. Enormous pressure on the species.

That severely limits diversity. Fine. But how long should it take to reestablish a level of genetic diversity? I'm assuming that once gene lines are gone, they're gone. The only way to introduce new genetic information - other some of the oddball ways viruses can alter DNA - is through a random level of mutation. Some sort of copying error during mitosis?

Is that correct? If so, how long, based on the numbers above, would it take to get back to a healthy level of diversity?
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Old 12-06-2018, 12:17 PM
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To explain my reference to the inverse square law.

Your number of parents follows 2n = x, or it grows by the power. While an approximation you still need to capture the "wash out" probabilities for receiving a single copy of a gene from a parent which is not 50% from the previous generation. The easiest way to approximate this for WAGs is to add another degree of freedom which leads you to the inverse square law.

For the spherical cow case or using Perturbation theory method of finding an approximate solution to a problem, by starting from the exact solution of a related, simpler problem.

You have three degrees of freedom, which leads to the inverse square lot for the simplest case of inheriting a single segment along a line. Not exact but good for base assumptions. FWIW, that is why sound waves and light fall off with the inverse square law, it is 3 spacial degrees of freedom to expand into and thus has n3 possible directions to expand in, which on one face ends up being the n2 area.

Your chances are less but I was trying to keep the math simple.

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Old 12-06-2018, 12:20 PM
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Tangential, but I'm interested in talking bottlenecks, here.

So say there WAS a bottleneck. 10,000 humans 100,000 years ago - or whatever the hypothesis is - all on the edge of extinction. Enormous pressure on the species.

That severely limits diversity. Fine. But how long should it take to reestablish a level of genetic diversity? I'm assuming that once gene lines are gone, they're gone. The only way to introduce new genetic information - other some of the oddball ways viruses can alter DNA - is through a random level of mutation. Some sort of copying error during mitosis?

Is that correct? If so, how long, based on the numbers above, would it take to get back to a healthy level of diversity?
Humans are amazingly similar even compared to other great apes. Genes wash out but I think the assumption you need to check in this case is that humans are diverse, which we are not.

The above mentioned theories are due to the mystery of the extreme lack of variety in the human genome.
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Old 12-06-2018, 01:45 PM
Jonathan Chance Jonathan Chance is offline
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But that doesn't really answer my question, does it?

Humans are genetically not diverse. Fine. But there's evidence other great apes are diverse. This implies that humans were more diverse in the past.

My question is how long would it take - assuming only the two systems outlined above for adding new genes to the mix - would it take to attain genetic diversity again?
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Old 12-06-2018, 01:57 PM
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But that doesn't really answer my question, does it?

Humans are genetically not diverse. Fine. But there's evidence other great apes are diverse. This implies that humans were more diverse in the past.

My question is how long would it take - assuming only the two systems outlined above for adding new genes to the mix - would it take to attain genetic diversity again?
You have to define what "genetic diversity" is, but the mean Minimum viable population estimates in this meta study was about 4169 individuals for a 95% chance of survival.

https://www.sciencedirect.com/scienc...534?via%3Dihub

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MVP with a median of 4169 individuals (95% CI = 3577–5129).
With human culture and an awareness of genetics 200 humans would be enough to have a 90% chance to repopulate the entire world by some accounts.

But when you have a bottle neck the "genetic diversity" is lost and wont' be re-created, new divergences may arise. But with policies like laws against inbreeding that diversity will be slower to grow as you won't have isolated populations.

This is all a gross simplification, but a smaller group of lets say 50 individuals may be able to re-populate the world it is just their chances of success go down. In fact a couple of family groups, if they didn't have any major recessive genetic traits which would cause collapse may be able to repopulate the world their chances of long term success are just much lower.

To be as clear as possible, the only reason we have groups that we can even claim are distinct is due to large amounts of inbreeding in fairly modern times. The minimal amount of diversity us humans have is because our family trees don't really branch much.

The minimal viable population could be as low as a pair of people in reproductive age if they get lucky on what genes they have and they were lucky in survival too.

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Old 12-06-2018, 02:04 PM
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To add to this, while the single migration model is in question in the Americas, the estimated effective size of the groups that peopled the New World is only around 70 individuals.
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Old 12-06-2018, 03:40 PM
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Tangential, but I'm interested in talking bottlenecks, here.

So say there WAS a bottleneck. 10,000 humans 100,000 years ago - or whatever the hypothesis is - all on the edge of extinction. Enormous pressure on the species.

That severely limits diversity. Fine. But how long should it take to reestablish a level of genetic diversity? I'm assuming that once gene lines are gone, they're gone. The only way to introduce new genetic information - other some of the oddball ways viruses can alter DNA - is through a random level of mutation. Some sort of copying error during mitosis?

Is that correct? If so, how long, based on the numbers above, would it take to get back to a healthy level of diversity?
Mutations during meiosis, not mitosis, are what matters for reestablishing a diversity of alleles. Mutations during mitosis do not get passed to the next generation.

IIRC, each person has, on average, around 64 recessive alleles.
And, on average, about 70 new mutations arise per generation. But many of those new mutations are non-coding or do not alter protein synthesis due to redundancy in the genetic code. And, much more rarely, a new mutation reverts a recessive allele to the dominant type.
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Old 12-06-2018, 05:34 PM
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I was wondering about this exact OP when the North Sentinel Islanders recently came into the news again. Seems to be a fairly closed group.
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Old 12-06-2018, 10:08 PM
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Another thing to remember though is that recessive traits will likely winnow out of a population longer term. For every 4 children on average with matching recessive genetic deficiencies, one will die, two will be carriers, and one will be healthy. And of those carriers married to a clean person, odds are only one in 4 of their children on average will be carriers. Before modern medicine, a lot of these problems took care of themselves. I imagine by the time the population reached Easter Island, many problem genes had weeded themselves out. (That would be an interesting simulation to try to program).

More insidious is something like Huntingdon's that doesn't show up until childbearing is over. Those problems may not go away, not so easily bred out.

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Old 12-07-2018, 12:43 AM
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Another thing to remember though is that recessive traits will likely winnow out of a population longer term. For every 4 children on average with matching recessive genetic deficiencies, one will die, two will be carriers, and one will be healthy. And of those carriers married to a clean person, odds are only one in 4 of their children on average will be carriers. Before modern medicine, a lot of these problems took care of themselves. I imagine by the time the population reached Easter Island, many problem genes had weeded themselves out. (That would be an interesting simulation to try to program).

More insidious is something like Huntingdon's that doesn't show up until childbearing is over. Those problems may not go away, not so easily bred out.
A few issues here...

A recessive carrier marrying someone who is "clean" (homozygous normal) has a 50% for each child of that union being a carrier, not 25%.

Second, not all recessive traits are lethal. So there is no guarantee that a child who inherits two recessive alleles will not have children.

Third, some traits seem to have a greater survival advantage in the heterozygous state. So a child who inherits one "normal" allele and one recessive allele may, on average, have more children than a child with two normal alleles. A recessive CFTR gene, which may cause cystic fibrosis in the homozygous recessive state, seems to offer a survival advantage in areas where cholera is endemic. Sickle Cell trait is another such gene, offering survival advantage in the heterozygous state in malaria endemic areas.

It is true that modern medicine may allow persons with two recessive genes to live longer and have more children than they would have without modern treatments thus increasing the gene frequency of the recessive allele in the general population.
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Old 12-07-2018, 04:26 AM
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I wonder - the original Easter Islanders were probably a single flotilla - one or two canoe-loads? This on top of a chain of expansion that meant the genetic diversity must have already been getting poorer and poorer as settlers moved east from island to island. Of course, these were big canoe-loads, so maybe 100 or more people? yet there do not appear to have been such problems in the Easter Island population that is believed to have peaked about 15,000.
It was not unknown for islander cultures to practice some rather stringent eugenics - that is, they did not permit the significantly deformed to live. IF you're willing to do that you can cut down on the bad genes floating around the population. It's not a perfect solution but it might be one reason we encounter small populations that manage to survive for long time periods.

Disclaimer: I have no idea if the Rapa Nui actually practiced infanticide or not, I'm just say it's a possible means to achieve a genetically healthy population with a small founder group. That doesn't mean it was used in a particular instance.
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Old 12-07-2018, 04:52 AM
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they did not permit the significantly deformed to live. IF you're willing to do that you can cut down on the bad genes floating around the population. It's not a perfect solution...
It's not a solution at all if the character is recessive. You could kill both the progeny and both parents without material effect on incidence.
Even for recessive lethals, the vast bulk of those genes are carried in the general population.
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Old 12-07-2018, 05:25 AM
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And that's with one-off unions. After a few generations of cousin marriage things get much worse. While a 3rd-cousin marriage is fairly safe, this should be a one-time deal. No repeats over each generation.
I suspect that in a lot of societies, most marriages involved people who were 3rd cousins or related more closely. I was raised in a rural area. When people were talking of someone, the conversation would almost always devolve in determining who is person was related to ("Wasn't his aunt X, who was your husband's cousin?") and a family link was found pretty much all the time. I'm pretty sure I was third cousin of or more closely related to most of the local population. And the local people definitely married each other.

And there are societies, even nowodays, where first cousin marriages are commonplace. I imagine that 3rd cousin marriages there must be repeated pretty often.

Is there really a dangerously high level of birth defects related to inbreeding in these societies?
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Old 12-07-2018, 05:36 AM
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While I am definitely of the modern mindset that cousin marriage is wrong
It's not a modern mindset, it's a cultural mindset. First cousin marriages aren't perceived with horror over here as they are in the USA (not sure if it's specifically an American thing or more generally an Anglo-saxon thing. Do British or Australians recoils at the idea of first cousin marriage?).


And I'm not sure how it's "wrong". Morally wrong? Because of the inbreeding? It seemed to me it was more a matter of "eww" factor than a matter of morals.
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Old 12-07-2018, 05:39 AM
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To clarify I was not referencing the Toba theory, which is disproved.
It is disproven? With certainty?
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Old 12-07-2018, 06:17 AM
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It's not a solution at all if the character is recessive. You could kill both the progeny and both parents without material effect on incidence.
Even for recessive lethals, the vast bulk of those genes are carried in the general population.
Well, yeah, like I said - it's not a perfect solution. It's actually pretty damn crude but if you're operating at low levels of tech there may not be a heck of a lot of alternatives.

Island societies also use infanticide as a form of population control. Not all of them, of course. Other "solutions" we continental folks in the modern world might find abhorrent include putting the old/crippled into boats and sending them off to sea to "discover" new islands, putting the old and infirm on ice floes during hard times/famine, and other unpleasant things. When you start studying what people used to do to survive you gain a better appreciation for the modern world and its alternatives to such methods.
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Old 12-07-2018, 06:21 AM
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And there are societies, even nowodays, where first cousin marriages are commonplace. I imagine that 3rd cousin marriages there must be repeated pretty often.

Is there really a dangerously high level of birth defects related to inbreeding in these societies?
Define "dangerous".

There is a detectably higher rate of birth defects/genetic disorders among societies with many first cousin marriages, but not to the point that those societies are in danger of extinction. The vast majority of people in such societies are fine and it's a sustainable mating practice over the long term.
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Old 12-07-2018, 08:04 AM
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In Iceland they take the risks of cousin marriage very seriously. There is a dating app so you can avoid accidentally getting romantically involved with your near cousins. Iceland is a leader in the field because of its small population size, low rates of immigration and comprehensive ancestral records. They can make a good estimate of how closely related two people are.

https://www.bbc.co.uk/news/av/techno...lose-relatives

Pretty soon genome decoding will be cheap enough for everyone to have it as part of their medical record and it should be possible to scan for two adults who want babies to scan for dangerous recessive genes rather than using fairly rough measures like cousins.

Lots of interesting ethical questions arise from genome decoding but also some huge medical benefits.

https://www.genomicsengland.co.uk/ab...enomes-project
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Old 12-07-2018, 08:52 AM
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But that's different from "a 2 to 3 percent greater risk". At least, if everyone involved is using the terminology consistently and correctly, which you probably don't want to take for granted.
I don't take it for granted which is why I look these things up. Media and 2nd hand reports often don't carefully specify these things. Looking at papers like the one I cited by Bennett and friends make this clear. They are specifying a percentage increase of overall risk.
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Old 12-07-2018, 01:17 PM
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I don't take it for granted which is why I look these things up. Media and 2nd hand reports often don't carefully specify these things. Looking at papers like the one I cited by Bennett and friends make this clear. They are specifying a percentage increase of overall risk.
If the overall risk was 3%, that's 3 out of a hundred. A 3 percent increase of overall risk would be 3.09 out of a hundred.

But even if the risk is doubled, that's just 6 out a hundred. Still not a huge amount, which is why statistics can be misleading even if precise terms are used.
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Old 12-07-2018, 01:43 PM
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Humans are genetically not diverse. Fine. But there's evidence other great apes are diverse. This implies that humans were more diverse in the past.

My question is how long would it take - assuming only the two systems outlined above for adding new genes to the mix - would it take to attain genetic diversity again?
My guess is that the intelligence and technological development of modern humans also reduced diversity levels by reducing the chances of separate populations staying isolated long enough to become substantially differentiated. And those same factors would prevent future populations from becoming substantially diverse. There is almost nobody anywhere anymore who is too far away to boink.
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Old 12-07-2018, 01:46 PM
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Another point to ponder is that the Sentinelese were likely trading with nearby islands until recently, which would we presume include "pedigree borrowing". One history I read about suggested that about 1300 ocean-going traffic from Indonesia and India started raiding the islanders for slaves; hence the current extreme hostility to outsiders. But the original inhabitants of the archipelago, again, are the extreme end of a migration out along the land bridge during the ice age about 30,000 years ago so not particularly diverse to start.
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Old 12-07-2018, 02:10 PM
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The estimated 50 and 400 Sentinelese individuals is enough. As I mentioned before an effective population size of around ~70 individuals was enough to populate all of the Americas in the past.
  #36  
Old 12-07-2018, 02:53 PM
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Originally Posted by Doug K. View Post
If the overall risk was 3%, that's 3 out of a hundred. A 3 percent increase of overall risk would be 3.09 out of a hundred.

But even if the risk is doubled, that's just 6 out a hundred. Still not a huge amount, which is why statistics can be misleading even if precise terms are used.
The papers I've checked, including my cite, say things like ~3% in general, another 3% for a total of 6% among 1st cousin offspring. (Depending on what they are looking for, etc.)

This is not that hard to check. I've done it here and in previous threads on this topic.
  #37  
Old 12-07-2018, 04:07 PM
Doug K. Doug K. is offline
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Originally Posted by ftg View Post
The papers I've checked, including my cite, say things like ~3% in general, another 3% for a total of 6% among 1st cousin offspring. (Depending on what they are looking for, etc.)

This is not that hard to check. I've done it here and in previous threads on this topic.
If the risk goes from 3% to 6% that's not a 3% increase in risk. It's a 100% increase. But double is only a huge jump if it was largish to begin with. 10% to 20% would be a huge jump, but from 3% to 6% is not.
  #38  
Old 12-07-2018, 04:15 PM
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Quote:
Originally Posted by Doug K. View Post
If the risk goes from 3% to 6% that's not a 3% increase in risk. It's a 100% increase. But double is only a huge jump if it was largish to begin with. 10% to 20% would be a huge jump, but from 3% to 6% is not.
This is a syntax discussion, stating it is a 3% increase in overall rate is far less ambiguous, and it also assumes that there are not other confounding factors.

If the mean rate for women is 3%, but the women is over 40 and thus has an increase in the overall rate of 4% the first cousin risk as an additive factor is no longer an 100% increase.

As the important number is the overall risk and not expressly the delta from the existing mean rate I would argue that the overall risk percentage is far more accurate and much less likely to be misinterpreted. That said if one was advocating for legal restrictions on marriage of first cousins the 100% figure would be a better figure for making that argument.
  #39  
Old 12-08-2018, 12:36 PM
Treppenwitz Treppenwitz is offline
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Originally Posted by clairobscur View Post
It's not a modern mindset, it's a cultural mindset. First cousin marriages aren't perceived with horror over here as they are in the USA (not sure if it's specifically an American thing or more generally an Anglo-saxon thing. Do British or Australians recoils at the idea of first cousin marriage?).
Here's a partial answer

https://en.wikipedia.org/wiki/Cousin...United_Kingdom

(Useful page all round).

To be honest, I wasn't particularly aware of this specific issue (first cousin marriage in immigrant communuties).

As a more general view from the UK I would say, yes it does occasionally happen, but it does raise eyebrows - it's tolerated but with a little bit of an intake of breath between the teeth, if you you know what I mean.

j
  #40  
Old 12-08-2018, 03:46 PM
Annie-Xmas Annie-Xmas is offline
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I asked the same question a while back

Incest: How close is too close?
  #41  
Old 12-08-2018, 04:09 PM
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Are the lower limits for source population based on exclusivity (monogamy)? Because it seems like a promiscuous group is going to be viable for a much smaller population.
  #42  
Old 12-09-2018, 02:11 AM
Hector_St_Clare Hector_St_Clare is offline
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To add to this, while the single migration model is in question in the Americas, the estimated effective size of the groups that peopled the New World is only around 70 individuals.
Correct me if I’m wrong, but there wasn’t just one “group” that peopled the new world. Navajos and other Na-Dene speakers etc. derived from a separate and much later migration event, right?
  #43  
Old 12-10-2018, 04:36 AM
filmstar-en filmstar-en is online now
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Here is a BBC documentary about cousin marriage amongst the Pakistani community in the UK and the health problems it causes.

'should I marry my cousin' https://vimeo.com/223139325

Cousin marriage is also tradition amongst Aristocracies in order to preserve a royal lineage in the days when being a member of a royal family, put on this earth to rule by divine ordinance was an important political advantage when it came to deciding who would be King.

https://therake.com/stories/code/ped...cratic-incest/

The same idea was adopted by some of the American corporate dynasties like the DuPonts and the Rothchilds.

I guess how safe it is depends very much on what nasty recessive gene lie lurking in the family genome.

The answer to that question is nearly solved as the cost of genome sequencing becomes cheaper and we learn how to assess the risk of congenital disease between two individuals accurately. Combine that with gene editing and IVR and the future presents some interesting ethical issues.

Some of these issues were explored in the SciFi movie Gattaca.

https://en.wikipedia.org/wiki/Gattaca
  #44  
Old 12-10-2018, 02:44 PM
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Re Pakistani intermarriage - From what I heard on a few documentaries a while ago, cousin (well, 2nd and third especially) is what builds the clans in some middle eastern communities. There are several groups, call them clans, or extended families or tribes or whatever (all loaded words). basically, the clans are extended families which reinforce the bonds with marriages to others of the same extraction, who tend to be moderately closely related. Thus you have many comingled but not usually related groups or families in the same general area.

it was suggested too that part of the Palestinian problem was not so much political or ideological, as inter-tribal conflict for dominance between different clans, some of whom support one faction or the other; hence the fight between Wes Bank and Gaza. Until they can agree to put old rivalries aside and work together, the region will be to fractured to agree among each other, let alone talk peace with an outside group.
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