What are the odds, if a pregnancy results from incest, that the offspring will have a birth defect?
I suspect that, if any organization has actual data on this, that the numbers might be skewed because of lack of a sufficient sample.
Anybody know?
What are the odds, if a pregnancy results from incest, that the offspring will have a birth defect?
As I understand it, there isn't a single simple answer to that. It would depend on a number of factors.
Is the family in question a carrier for a known but recessive genetic defect?
inbreeding does not generally cause genetic mutations, but it will amplify otherwise recessive traits.
The risk increases when it is repeated across multiple generations.
If your mother is also your sister, you are probably okay. If you have two sisters, one who is also your mother and one who is also your grandmother, you might have a problem.
Given the legalities (or lack there of) of human incest, if you want a quantifiable answer, look for research on controlled in-breading in domesticated animals.
Given the legalities (or lack there of) of human incest,
Or just look at the European Royal families.
Or just look at the European Royal families.
Not a good sample for a scientific study.
Not a good sample for a scientific study.
Or for actually being effective leaders, either.
Or for actually being effective leaders, either.
True, but from a stand point of studying reproductive risk to first generation incest, the European royal families are a population with centuries of multi-generational inbreeding.
Or just look at the European Royal families
the best known historical example is Habsburg jaw, or Habsburg or Austrian lip, due to its prevalence in members of the house of Habsburg.
The prognatism of the last Spanish Habsburg king Charles II. (1661-1700) was extreme. Six of his 8 great-grandparents were borne Habsburgs and the seventh a Wittelsbach with a Habsburg mother.
His Habsburg jaw was so extreme that he had severe problems with speaking and chewing.
HM.
he prognatism of the last Spanish Habsburg king Charles II. (1661-1700) was extreme.
Again, centuries worth of multi-generational inbreeding, not the result of a single instance of first generation incest.
Interesting, but not really relevant to the question the OP asked.
Again, centuries worth of multi-generational inbreeding, not the result of a single instance of first generation incest.
Interesting, but not really relevant to the question the OP asked.
Actually, he didn't specify if it was a simple and single brother-sister knock-up, or something ongoing. That was your own decision that studies of generations of inbreeding (meaning incest) are irrelevant.
IIRC with a first generation, the risk is roughly double that of the general population. but if it continues the risks raise quite quickly.
I'm not sure what's riskier, Parent/Child or Siblings.
Cousins are a different kettle of fish especially 'double cousins'.
There is a 'couple' in Germany who are Bro/Sis and they have a few kids together. He has served multiple sentences for incest due to demonstrable kids together. I remember some of them have developmental issues. So it's not without risk and just looking at recessive traits is not the whole 'story'.
As you would expect there are practically no studies on this topic as it stands. but I'm sure there must be at least a few out there.
there are practically no studies on this topic as it stands. but I'm sure there must be at least a few out there.
If you find a study done by the Church, ignore it. They will be biased.
Cousins are a different kettle of fish especially 'double cousins'.
'Double Cousins' can be one of three types.
1) The Moms are identical twins and the Dads are identical twins - same risks as siblings.
2) One set of parents is identical twins the other not. The risk is less than in the first case, but higher than cousins.
3) The cousins share paternal and maternal grandparents, but neither their Moms or Dads are identical twins. Risk is less than in the second case, but higher than just random cousins.
IIRC with a first generation, the risk is roughly double that of the general population.
The risk for the general population (baring one or both of the parents having known genetic defects) is so small that double the risk is not really significant.
I'm not sure what's riskier, Parent/Child or Siblings
Parent/child has guaranteed 50 % duplication of genes. Possibly more if BOTH parents are genetically close.
Siblings can have from near 0% to near 100% match.
The royal families of Europe married each other for centuries. It's common for a Muslim to marry a first cousin today (I know this from a friend in Pakistan who is marrying her first cousin).
It's common for a Muslim to marry a first cousin today (I know this from a friend in Pakistan who is marrying her first cousin).
I did some research on US state laws on this for a story I started but haven't posted.
Most US states restrict first cousin marriages, but a few don't.
Colorado, for example, allows unrestricted first cousin marriages.
My home state (Wisconsin) Allows first cousin marriages given certain significant restrictions are met. It would be allowed if the woman is post-menopausal or if at least one of the couple has medical proof of sterility.
It's common for a Muslim to marry a first cousin today
I'm a christian from Iraq and lived among muslims where cousin marriage is a very common thing. I don't recall seeing an unusual level of birth defects compared to the west.
I can't comment on siblings incest or parent/child incest as that is punishable by death in Iraq if it were to become public.
I have two aunts (sisters) and they married their first cousins (two brothers) and they had 8 normal children. Although, our family doesn't have a history of cousin marriages so they were an oddity.
It's common for a Muslim to marry a first cousin today (I know this from a friend in Pakistan who is marrying her first cousin).
That supposedly doubles the risk of birth defects from 3% to 6%, according to the first few results returned by Google. The UK encourages counselling for South Asians who want to marry cousins, but in the Muslim population particularly there's a feeling that it's Allah's will that matters. The UK's birth-defect hotspots coincide with high South Asian populations.
AJ
Unless there is something along the lines of hemophilia or other recessive gene, it's still only around 5-6% for any random actual brother and sister, versus the 1-3% chance for any two random strangers. If the gene pool doesn't expand very much in later generations, the odds will increase.
Also, how many of these defects are environmentally triggered rather than biologically? Many areas where there is a high level of incest also have high levels of ground/air pollution. Could some of that pollution based abnormality be miss-represented as of a biological nature?
Anyone who has kept pets will know that they don't care if they are siblings or parent/child. In nature there are no restraints. If genetic damage through incest was really such a critical biological factor, then why don't we see pods of dolphins all with horrendous abnormalities? Or indeed any other animal that uses a social/familial structure.
I'm not denying that any inheritant DNA errors have the potential to spiral out of control, but surely the opposite also runs true, that beneficial traits will also proliferate?
DNA changes manifest themselves faster in organisms with a shorter lifespan, so you will see the effects in wildlife long before you would see it in humans, especially since the average human generation is about twenty seven to thirty years. Much longer than most animals.
If genetic damage through incest was really such a critical biological factor, then why don't we see pods of dolphins all with horrendous abnormalities? Or indeed any other animal that uses a social/familial structure.
It might be because a young dolphin with 'horrendous abnormalities' are less likely to survive to adulthood.
because a young dolphin with 'horrendous abnormalities' are less likely to survive to adulthood
Good point.
Anyone who has kept pets will know that they don't care if they are siblings or parent/child. In nature there are no restraints. If genetic damage through incest was really such a critical biological factor, then why don't we see pods of dolphins all with horrendous abnormalities? Or indeed any other animal that uses a social/familial structure.
Because you can't equate the behavior of animals in captivity to wild animals. Most studies show that wild animals in almost all cases practice incest avoidance behavior. The same is not true of domestic animals - if for no other reason than they don't have the ability to do so - they are confined with a small population of other animals almost all of which are related. The same mistake was made in the studies of wolf pack structure. They tried to use observations from captive animals to theorize about the pack behavior in the wild and were completely wrong.
Because you can't equate the behavior of animals in captivity to wild animals. Most studies show that wild animals in almost all cases practice incest avoidance behavior
True for the first part, not for the second. Both DNA evidence taken from wild animals and observations of lion prides in Africa and wild deer in Scotland, as well as others, have proven that animals don't care. And will quite happily indulge in incest when the mood takes them. This is also true of apes, who indulge in sex for pleasure as well as procreation.
True for the first part, not for the second. Both DNA evidence taken from wild animals and observations of lion prides in Africa and wild deer in Scotland, as well as others, have proven that animals don't care.
That appears to be dependent on how long it takes for critters of a particular species to forget familial relationships. I remember that cats have to be separated relatively early if you don't want siblings knocking each other up, dogs have longer.
AJ
Its a well known psychological force. people who 'grow up' together generally have a built in aversion to each other sexually. sorry can't remember what its called.
but conversely relatives who are separated early on and meet in adulthood frequently have genetic sexual attraction issues. I don't have any numbers to back up that claim, but I've read up on it a bit. Its also a well understood affect.
There is a Czech study that compared the children born of incestuous with the children born of the same mothers in non-incestuous relationships. The children of the incestuous relationship had much more problems than the others. Higher mortality, retardation, birth defects.
https://www.jstor.org/stable/45100818
might be skewed because of lack of a sufficient sample
I think that would be an accurate assumption.
I've read that Josef Mengele and Aribert Heim conducted experiments along those lines, along with the Japanese unit 731 from WW2.
Those would have been the only studies of sufficient sample size. However, any and all results from them have long since been buried deep.
There has been some studies since then, but any information from them would be suspect at best for political reasons.
