People Choose Spouses With Similar DNA

[Aberdeen]

I think for the norm we have to go back to small hunter gatherers tribes. They did it for couple of millions of years.

I would say that some of the small Paleolithic hunter/gatherer clans probably suffered from too little genetic diversity.

 

[Angela]

I would say that some of the small Paleolithic hunter/gatherer clans probably suffered from too little genetic diversity.

I would agree with that. The same point was made about the Neanderthals in a recent paper wasn't it?

Even with regard to these isolated island or mountain communities, I think it very much depended on what the founders brought with them in terms of genetic material. There are some relatively inbred such communities which suffer from a whole series of genetic defects, while others are remarkably free from them. The Sardinians, despite the high incidence of longevity, are one such group. The French Canadians are another example; their fertility rates in the early years of settlement were extraordinary, but they also are, relatively, prone to certain recessive disorders.

 

[LeBrok]

I would say that some of the small Paleolithic hunter/gatherer clans probably suffered from too little genetic diversity.

It depends on environment. If it is steady, you don't need genetic diversity. Genetic sameness is pretty good and suiting static environment. However these groups are less prepared to sudden environmental changes, slow to adapt to them, and in greater danger of dying off than others when changes happen.

 

[Aberdeen]

I would agree with that. The same point was made about the Neanderthals in a recent paper wasn't it?

Even with regard to these isolated island or mountain communities, I think it very much depended on what the founders brought with them in terms of genetic material. There are some relatively inbred such communities which suffer from a whole series of genetic defects, while others are remarkably free from them. The Sardinians, despite the high incidence of longevity, are one such group. The French Canadians are another example; their fertility rates in the early years of settlement were extraordinary, but they also are, relatively, prone to certain recessive disorders.

Yes, a study of Neanderthal DNA actually suggested that inbreeding and lack of genetic diversity may have contributed to the decline of the Neanderthals. As for French Canadians, there's certainly an issue with inbreeding and recessive illnesses in relatively isolated communities such as those in the Saguenay region. It isn't really an issue in more urban areas and less isolated rural areas, because of immigration over the years, settlers from England and Scotland, and also huge numbers of Irish orphans being adopted by French Canadian families during the Irish Potato Famine. The Irish children were sent to French families because the orphans were almost all Catholics, and mostly grew up speaking French and carrying the names of their adoptive families, but they did inject a lot of new blood into Quebec, even if the Irish peasants at that time were probably quite inbred themselves. There's a big problem with inbreeding and recessive diseases in Newfoundland and Labrador, where most people are descended from settlers who moved there during the period 1400 - 1600 AD - the Bristol merchants were fishing in Newfoundland and even settling there before Columbus, although they were initially very secretive about it, to protect their source of cod. So pretty much everyone in Newfoundland is related to everyone else, except for the small minority who've settled there in the last 100 years or so. And of course the inbreeding of the European royals is a whole saga in itself.

 

[oriental]

I think those "dwarfs" with short arms and legs all being 4 feet or less tall are inbred offsprings.

 

[LeBrok]

Yes, a study of Neanderthal DNA actually suggested that inbreeding and lack of genetic diversity may have contributed to the decline of the Neanderthals. As for French Canadians, there's certainly an issue with inbreeding and recessive illnesses in relatively isolated communities such as those in the Saguenay region. It isn't really an issue in more urban areas and less isolated rural areas, because of immigration over the years, settlers from England and Scotland, and also huge numbers of Irish orphans being adopted by French Canadian families during the Irish Potato Famine. The Irish children were sent to French families because the orphans were almost all Catholics, and mostly grew up speaking French and carrying the names of their adoptive families, but they did inject a lot of new blood into Quebec, even if the Irish peasants at that time were probably quite inbred themselves. There's a big problem with inbreeding and recessive diseases in Newfoundland and Labrador, where most people are descended from settlers who moved there during the period 1400 - 1600 AD - the Bristol merchants were fishing in Newfoundland and even settling there before Columbus, although they were initially very secretive about it, to protect their source of cod. So pretty much everyone in Newfoundland is related to everyone else, except for the small minority who've settled there in the last 100 years or so. And of course the inbreeding of the European royals is a whole saga in itself.

Let's listen to other side of the inbreeding story a bit:

Let's take a look at some actual figures to see what the real risks are. Perhaps the best example is the work of Professor Alan Bittles, an adjunct professor at the Centre for Comparative Genomics at Australia's Murdoch University, who has worked on the subject for over three decades and in 2008 conducted a review of forty-eight studies from eleven countries on the rate of birth defects in the children of first cousins.
He found that increased risks do exist, but not nearly to the extent that we might imagine. While there's about a 2% risk of birth defects in the general population, first-cousin children have about a 4% chance. Of course, you can phrase that in any number of ways, depending on how you want to spin it. On the one hand, that means that there's double the risk of birth defects in the children of first cousins. On the other hand, 96% of such children are born completely healthy, which is still the vast majority.
What's more, Professor Bittles found that only 1.2% suffered increased infant mortalityrates. Generally speaking, these are marginal increases we're talking about, hardly the sort of guaranteed horrific outcomes that are often associated with inbreeding. But all that shows is that inbreeding isn't as bad as we often think - a statement worth making to be sure, but probably not totally earth-shattering. To that end...

Whole article:
http://io9.com/5863666/why-inbreeding-really-isnt-as-bad-as-you-think-it-is

Also there are situations when encouraging recessive traits proliferation by inbreeding, might be good for population. Alleles for very white skin and lactose tolerance might have received a helping hand thanks to close relationship between people in small tribes or villages. I guess, as long as we skip inbreeding to second cousins not much harm happens.