Why not marry your cousin? Millions do

Apr 25, 2012

The health risks of marrying a cousin have been grossly overstated, says a new book.

A better understanding of the health effects of cousin marriage could mean more appropriate marriage laws and better medical care for cousin couples and their children.

In 'Consanguinity in Context,' author and medical geneticist Alan H. Bittles of Murdoch University in Australia examines common misconceptions about cousin marriage from legal, cultural, religious and medical perspectives.

Marriage between cousins is taboo in much of the Western world. In the United States, 31 of 50 states outlaw marriage between first cousins, or allow it only under certain circumstances.

Although cousin marriage is banned in much of the US, the practice is tolerated and even encouraged in other parts of the world. In South Asia and the Middle East, for example, 20-50% of marriages are between first cousins or even closer relatives. They're in good company. More than 10% of people worldwide are married to a second cousin or closer, or have parents who are cousins.

and his wife Emma were first cousins. Darwin's grandparents were cousins too.

Cultures where cousin marriage is common point to its social and economic benefits, such as strengthening family ties and keeping wealth in the family.

Opponents argue that first cousin marriage increases the risk of passing on . But for Bittles, 35 years of research on the health effects of cousin marriage have led him to believe that the risks of marrying a cousin have been greatly exaggerated.

There's no doubt that children whose parents are close biological relatives are at a greater average risk of inheriting genetic disorders, Bittles writes. Studies of cousin marriages worldwide suggest that the risks of illness and early death are three to four percent higher than in the rest of the population.

But the risks apply primarily to couples who are carriers of disorders that are normally very, very rare, Bittles explained. "For over 90% of cousin marriages, their risk [of having a child with a genetic abnormality] is the same as it is for the general population," he said.

What's more, many studies of the effects of cousin marriage fail to account for the influence of non-genetic factors on infant health, such as socioeconomic status, maternal diet during pregnancy, and infections. "Many of the data are exceedingly poor," Bittles said.

Some degree of inbreeding has been the norm for much of human history.

Scientists estimate that the first people to migrate out of Africa numbered 700 to 10,000 breeding-aged individuals. Given those small numbers, and the fact that these people likely dispersed in small hunter-gatherer groups and often married within their clan or tribe, "it seems inevitable that some level of close kin mating would have occurred," Bittles writes.

"If you marry within your community, there's not a lot of people to choose from," he added.

Bittles is now studying the effects of kin mating in early humans and the genetic consequences for people living today at the U. S. National Evolutionary Synthesis Center in Durham, North Carolina.

One surprising and oft-neglected advantage of marriage between close biological relatives is a phenomenon called purging, in which disease genes are exposed and removed from the gene pool.

Thanks to purging, marriage between close relatives in early human populations would have kept the prevalence of genetic disorders low, Bittles explained.

Today, cousin marriage is on the rise in regions with a large influx of immigrants from areas where the practice is more common, such as North Africa, the Middle East, and Central and Southern Asia.

But in the long-term, shrinking family sizes and increased mobility in many parts of the world means that cousin marriage is likely to decline. In the absence of purging, harmful genetic variants could accumulate over time.

"We may be creating a problem for ourselves in future generations," Bittles said.

Explore further: Newlyweds, be careful what you wish for

More information: The book will be published by Cambridge University Press on May 7, 2012.

Provided by National Evolutionary Synthesis Center (NESCent)

3.6 /5 (16 votes)
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User comments : 20

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YabancIst
2.5 / 5 (8) Apr 26, 2012
Why not eat shit? Trillions of flies do. Sorry, but the title of this piece is even more inane than its content. And to mention Darwin in an article downplaying the genetic effects of first cousin marriages is particularly ironic: He spent his life in severe illness (still controversial exactly what) and his daughter died as a child, most likely due to congenital defects. Sure most first-cousin couples have healthy children (so do some sibling couples), and sure biologists (eugenicists?!) should not meddle with individual's choices, but actively advocating a practice which is also socio-culturally oppressive is really astounding...
kochevnik
2 / 5 (4) Apr 26, 2012
Isn't incest used to keep breeds in line with expectations?
Bigbobswinden
5 / 5 (2) Apr 26, 2012
A town in Britain has real trouble with baby's born with genetic problems due to constant family intermarriage. As told to me there is little or no problem the first time interrelated family members marry but the effects build up fast on subsequent occasions.
kevinrtrs
1 / 5 (14) Apr 26, 2012
The real irony is of course that ALL human beings are related - otherwise there would be some really interesting problems with procreation. Here it would be extremely difficult to show how evolution was responsible for this: it cannot account for sexual differences and never in anyone's wildest dreams can evolutionary processes conjure up the complex genital and procreation organs.
It remains for evolutionists to demonstrate just how such organs could arise from random processes. Good luck with that.
kochevnik
3.7 / 5 (9) Apr 26, 2012
The real irony is of course that ALL human beings are related
No doubt in your town.
A town in Britain has real trouble with baby's born with genetic
Yes like the problem of hemophilia in the royal family. Apparently purging didn't work for them.
DaFranker
5 / 5 (6) Apr 26, 2012
The real irony is of course that ALL human beings are related - otherwise there would be some really interesting problems with procreation. Here it would be extremely difficult to show how evolution was responsible for this: it cannot account for sexual differences and never in anyone's wildest dreams can evolutionary processes conjure up the complex genital and procreation organs.
It remains for evolutionists to demonstrate just how such organs could arise from random processes. Good luck with that.

It's not difficult. Try studying genetics for a few years and you'll have all the answers.
physorgname
4.2 / 5 (5) Apr 26, 2012
Why not eat shit? Trillions of flies do. ..


I think the author was talking about human activities. However you're free to do as you please.
Anorion
2.3 / 5 (6) Apr 26, 2012
i heard many religious groups practice that, indeed that explain a lot...
kaasinees
1 / 5 (2) Apr 26, 2012
Monkeys eat elephant shit.
Musashi
3.4 / 5 (5) Apr 28, 2012
"The real irony is of course that ALL human beings are related"

No, but your parents definitely were...
Lurker2358
2.5 / 5 (2) Apr 29, 2012
No, but your parents definitely were...


There are supposedly 4 known maternal lines in Mitochondrial DNA, which ironically agrees with the Biblical Flood story's genetic bottle neck, since the story claims there were 4 women on the Ark.

I don't know what to make of the flood story, but it is interesting that the conditions of the story meet the criteria needed to sustain the 4 branches of human Mitochondrial DNA.

The exact details of this event are not important, except that one detail in this flood, genetic bottleneck story happens to be precisely what it would need to be to produce the observed genetic evidence.

This bottleneck event happened, in some fashion, even though the exact details are lost to history.

So you have genetic proof that all humans are definitely descended from a population containing as few as 4 original females.

Why would it be such a stretch to believe the 4 maternal lines had diverged enough in the years since the one "Eve"?
TheGhostofOtto1923
3 / 5 (6) Apr 29, 2012
The real irony is of course that ALL human beings are related - otherwise there would be some really interesting problems with procreation. Here it would be extremely difficult to show how evolution was responsible for this: it cannot account for sexual differences and never in anyone's wildest dreams can evolutionary processes conjure up the complex genital and procreation organs.
It remains for evolutionists to demonstrate just how such organs could arise from random processes. Good luck with that.
More lies from a paid spokesman. Why dont you get an honest job?
TheGhostofOtto1923
2 / 5 (4) Apr 29, 2012
There are supposedly 4 known maternal lines in Mitochondrial DNA, which ironically agrees with the Biblical Flood story's genetic bottle neck, since the story claims there were 4 women on the Ark.
Well I think this would be consistent with the idea that our species was engineered by aliens, but unless you begin posting links for the info you post I feel justified in calling you a LIAR as I dont think I need to find them myself.
Lurker2358
1 / 5 (1) Apr 29, 2012
Well I think this would be consistent with the idea that our species was engineered by aliens, but unless you begin posting links for the info you post I feel justified in calling you a LIAR as I dont think I need to find them myself.


"The Human MRCA. All humans alive today share a surprisingly recent common ancestor, perhaps even within the last 5,000 years, even for people born on different continents." - Wikipedia, Mitochondrial Eve.

That is very, very close to the Biblical timeline, but does not agree exactly.

"each present-day human has exactly the same set of genealogical ancestors" alive at the "Identical ancestors point" in time. This is far more recent than Mitochondrial Eve

Lurker2358
1 / 5 (1) Apr 29, 2012
There are supposedly 4 known maternal lines in Mitochondrial DNA, which ironically agrees with the Biblical Flood story's genetic bottle neck, since the story claims there were 4 women on the Ark.
Well I think this would be consistent with the idea that our species was engineered by aliens, but unless you begin posting links for the info you post I feel justified in calling you a LIAR as I dont think I need to find them myself.


I am not a liar.

I was not claiming that it literally agrees with the flood story, only the concept of a bottleneck at some point.

As for the other details I gave, I seem to recall it from a Discovery channel documentary.

the net result might not have been caused by a single bottleneck, since you have to figure pandemics and wars and genocides, etc.

In the ancient times, they used to capture the women and keep them as slaves or wives, and murder the men, so the paternal lines would generally die out more often than maternal lines.
Lurker2358
1 / 5 (1) Apr 29, 2012
One of the reasons polygamy existed in the ancient world for thousands of years, maybe even tens of thousands of years, is because about the only thing men did back then was kill one another, and take their enemy's wives as their own.

You can also find a reverse case in the Bible, where the Israeli hypocrites were supposed to have been avenging the death of a woman that was gang raped, and instead they flanked the Benjamites army and torched the city and murdered all the women and children, and left the men who were the original offenders alive.

Unfortunately, that's human history, who the hell would admit that about their own people's history unless it was based on the truth? Nobody would make up a lie and admit to an atrocity like that.

But it's a perfect example of genocide and how that can change the genetics of a population forever.

Oh, by the way, on that other thread, Abraham married his half-sister, Sarah, they were Hittite and Ammorite.
TheGhostofOtto1923
3 / 5 (8) Apr 29, 2012
I am not a liar.
No? Then where did you get this?
There are supposedly 4 known maternal lines in Mitochondrial DNA
Be polite and reference what you post. Your 'Eve' link is NOT this. I suspect that these 4 lines originate millions of years ago, in which case your flood comparison is nonsense, and you know it.

Post a reputable link or STFU.
ryggesogn2
1 / 5 (2) Apr 29, 2012
Marriage has nothing to do with children anyway so why bother with any such laws?
Lurker2358
2.3 / 5 (3) Apr 29, 2012
I am not a liar.
No? Then where did you get this?
There are supposedly 4 known maternal lines in Mitochondrial DNA
Be polite and reference what you post. Your 'Eve' link is NOT this. I suspect that these 4 lines originate millions of years ago, in which case your flood comparison is nonsense, and you know it.

Post a reputable link or STFU.


I'm not required to post an exact reference, because I didn't claim the idea as my own, and I did mention it was on Discovery Channel.

How the hell would I know who to credit on something I saw several years ago, randomly on a documentary?

You're really annoying, Ghost.

If it matters to you that much, look it up for yourself.

I'm sick of wasting my time for your sake, because we both know I always find that reference, and you NEVER apologize for being a jackass or falsely accusing me.

STFU yourself.
TheGhostofOtto1923
3.4 / 5 (5) Apr 30, 2012
I'm not required to post an exact reference, because I didn't claim the idea as my own, and I did mention it was on Discovery Channel.
And I am not required to refrain from calling you a liar when you post unsubstantiated info and personal opinions. Real scientists and celestial mechanics would not be so capricious.

I do understand that you often regard your opinions as fact. This is annoying.
I'm sick of wasting my time for your sake, because we both know I always find that reference
Translation - 'I looked and realized I was wrong.' Much like your unresearched claims for dry ice in the Antarctic.
you NEVER apologize for being a jackass or falsely accusing me.
I have. I think last time my exact words were 'I stand corrected.' Remember?

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