Sunday, 5 January 2014

Incestuous Creationist Absurdity

Arthritic and inbred

Image: John Reader/Science Photo Library
Inbreeding shaped the course of human evolution - 28 November 2013 - New Scientist

Every now and then, well, to be frank, more often now than then, science throws up something which makes religion and especially creationism look even more idiotic.

Take this article in New Scientist, for example.

It seems that one of the things preventing human progress after we had diversified out of Africa into the relative vastness of Euro-Asia was the fact that we tended to live in small, isolated groups. This meant there was a great deal of inbreeding with incest or near-incest being common.

This had two consequences: the first being genetic; the second cultural.

Inbreeding tends to make genetic defects more common in a population by increasing the probability of a baby inheriting a recessive gene from both its parents. It also retards the spread of new genes and so tends to reduce genetic diversity. Even when there is exchange of mates - usually females - between neighbouring groups, with small scattered groups being the norm there is still a substantial barrier to the spread of genes throughout the entire species.

This of course means we would expect to see geographical variation as localised populations evolve according to local factors and as the result of founder effects. Not surprisingly, this is exactly what we do see.

The second problem is perhaps a little harder to appreciate. Humans are almost unique in that we retain technological advances and pass them on to our offspring in the form of education and training. This meant that, before the advent of writing, skills and knowledge were retained in the minds of mostly the older members of the groups. If they were lost the group lost this skill and knowledge. This could explain why there is archaeological evidence that skills such as bone-working appear to have arisen and then been lost over time in different groups.

So, existing as we did in small incestuous groups we would have tended to suffer from lack of genetic diversity and an ephemeral technology having to constantly reinvent techniques. It was only when the population reached some critical mass that we were able to 'take off' technologically, and then greater mobility would have led to more rapid gene migration and increased genetic diversity.

This could explain why we seemed to have 'exploded' soon after the discovery of agriculture and metal working. It's an example human gene-meme co-evolution in fact.

So how does this make biblical creationism look even more idiotic?

Well, according the the Bible, humans went through two periods in the space of a couple of thousand years, and only a few thousand years ago, in which we were reduced to not just small groups of a few hundred or maybe a few thousand individuals living in geographical isolation, but to single families without even a neighbouring group a fews days walk away with whom to exchange genes and technology.

Such small groups would have been obligatorily incestuous and so biologically non-viable. They would also have quickly lost what few skills they had chanced to have developed or, in the case of Noah's tiny family, those skills and knowledge they had happened to have acquired before the Flood.

The idea that the human species, and human technology, could have evolved from such small, genetically and culturally narrow groups, not just once, but again a couple of thousand years later, is absurd.

The same applies, so far as genetic diversity is concerned, for every other species too, of course.

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  1. As I've had occasion to state more than once in the past, if the story of Genesis - and Cain - is to be taken at face value, we are all the children of a motherf***er.

    Thanks for following me, by the way. It's an honour.

  2. Yes, if taking a literal reading of the Genesis creation and flood stories, then yes, there was a lot of incest and inbreeding, as I've found often-disagreeing religionists readily agree and admit.

    However, genealogists, historians, and anyone who can do math say we have a lot of inbreeding in our not-too-distant past. With each previous generation you trace back, the maximum possible number of your genetic ancestors doubles. You can have 2 parents, up to 4 grandparents, up to 8 great-grandparents, up to 16 great-great-grandparents, etc.

    On average, there are about four generations per century. For people born in the year 2000, their 8 great-great-grandparents were probably born around 1900. Sometime around 1800 their great-great-great-great-great-great-grandparents were born (there may be up to 128 of them). About 29 generations back, or roughly around the time of 1250-1300, the total number of your possible ancestors for that generation equals or exceeds the total population of the planet, which was about 500 million people.

    What gives? Well, first of all, if all 500 million of those people were your ancestors, they would also be the ancestors of all of the rest of us, too.

    Secondly, you probably don’t have every person alive back then as your ancestor. There wasn’t a lot of interracial or intercultural parenting going on back then. People were more isolated, more people lived in rural countrysides rather than dense urban areas, and people were not nearly as geographically or socially mobile as they are today. It was very common for a person to be born in and to die in the the same village or town, having lived all of her or his life there.

    This means that for many, many, many, many generations, there was a lot of what most people would call today “inbreeding.” If your spouse wasn’t your first cousin, your spouse was likely a second or third cousin, or a second cousin-once removed, our even your double-cousin, etc. Not only did these things not destroy humanity, but in Europe, the Renaissance was birthed in these conditions.

    Coming back to around 1800, very few people are likely to have 128 great-great-great-great-great-great-grandparents, just like very few of those people in 1800 had 128 of them in 1600. Because chances are, some of your recent ancestors were cousins, if not closer. If you marry your first cousin, you have no more than six genetic grandparents between you, instead of eight. If your parents are first cousins, you have six great-grandparents instead of eight.

  3. Indeed.

    And this of course explains how beneficial mutations can be concentrated up an improbability gradient because leaving more descendents means they will be more likely to appear in our direct ancestry.

    However, it says nothing about the point of the blog which was that humans existed throughout much of Euro-Asia in small groups of a few thousand individuals and that this was detrimental as evidence by the increased number of inherited defects are found in the fossil record and a lack of genetic diversity found in the DNA records, and that the absurd creationist myth includes two such periods of highly incestuous inbreeding closely following one another, the second being the product of the first and so would have exacerbated the already serious problem of lack of genetic diversity caused by everyone being descended from just two people, one of whom was supposedly a clone of the other - idiotic though that claim might be.


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