Monday, April 30, 2012

Genetic Anomalies Due to Inbreeding?

A reader (I'll live him anonymous for now, unless he wants credit) wrote:
Reading last May's "Where is the Promise of Christ's Coming?" , the question came to me: how do we square the facts of closely-related "inbred" lines in genealogy with the Biblical fact that all of humanity descends from Adam via the eight of the Ark?

We know from the condition of the Habsburgs that such close relations lead to deformities and even mental incapacity (Charles II) over the span of less than 500 years of that family's history. Has humanity overall been preserved from this biological fact which interbreeding seems to engender over long periods of time? Was this simply a curse of God on the Habsburgs?

How do the 8 saved in the ark translate to the ~7 billion of today with such varied racial characteristics? It seems contradictory.
First, the Bible does indicate to us that human lifespan has dramatically decreased from the multiple century lifespans before the flood to the sub-century typical lifespans after the flood, and even today. Whether this is due to genetic corruption from an early period of "in-breeding" or whether it is due to changes in the Earth's protection from solar radiation associated with the Great Flood (something I've heard AiG types suggest), there has been some significant change to human life.

While I understand what you mean by "racial characteristics," it needs to be recognized that categories like "race" are largely conventional. Typically, pronounced physical differences are associated with relatively isolated groups. This isolation does tend to reinforce particular physical characteristics that are less common outside the group.

An example that most people may think of is the Pygmy people group, while the blue skinned people would be another less well known example. In God's providence, neither of those groups ever got large enough to be referred to as a "race," but the basic principle is the same.

Thus, "in-breeding" (very loosely defined) of each group may help to explain the very distinctive appearance of Europeans as compared to sub-Saharan Africans, peoples of the Indian sub-continent, and far-east Asians (to take some examples).

The Bible explains that at Babel language confusion resulted in dispersion of people from the tower. Moreover, in the days of Peleg the world was divided. This dispersion and division tended to have the result of people groups becoming more segregated and distinctive. It's not totally clear how uniform in appearance the pre-Fall humans were, but even if they were all quite similar in appearance to one another, this post-fall dispersion and segregation would be expected to produce groups with distinctive looks after a number of generations.

We all derive from one pair of adults (Adam and Eve), and also from a maximum of 8 grandparents (Noah and his wife and the in-laws of their three sons), all of which are descendants of that original pair. This led to some measure of marrying one's close relatives for a number of generations. However, over time this necessity decreased. Thus, by the time of Moses, there were prohibitions on marrying one's half sister, although only about seven generations earlier Abraham had married his own half-sister, though clearly there was already stigma associated with marrying a full-blooded sister at that time.

Why then are we not all then deformed? First, as the relationships become more distant, inbreeding does not invariably produce and emphasize harmful, recessive mutations. Second, the "survival of the fittest" principle applied to a large extent in pre-socialistic societies. Those with physical and/or mental defects would tend to remove themselves from the gene pool in a variety of ways. Thirdly, it is entirely possible that human genetics were not as prone to mutation before the fall, and that they only gradually became prone to mutation after the fall. For example, if the mechanism that produces a short life is also the mechanism that leads to harmful mutations, and if that mechanism is solar radiation, then it seems possible that there was no significant genetic risk to mutation before the fall.

A lot of this is, of course, speculation. God does not necessarily give us the answers to all these questions. We have no way of knowing whether the Hapsburg family was specially cursed by God, or whether their condition had some other purpose in God's plan. Whatever the answer to that question, since the history of man before and after the flood does not require men to marry their first cousins or full blooded sisters for many successive generations, the risks associated with in-breeding today among a population of 7 billion derived from an original pair is small.



Truth Unites... and Divides said...

"We all derive from one pair of adults (Adam and Eve), and also from a maximum of 8 grandparents (Noah and his wife and the in-laws of their three sons),"

Couple the above with Global Flood and YEC, then think of the difficulties and distances of migration and the enormously quick micro-evolution which had to occur to obtain such differentiation between various races, and it becomes hard to conceptualize. Not saying that that didn't occur, but that it seems difficult to conceive.

Steve Drake said...

Dr. Andrew Snelling in "Earth's Catastrophic Past", Vol. 1 of 2, Institute for Creation Research, Dallas, 2009 has a very plausible reason how this occurred. Couple that with population statistics if modern homo sapiens sapiens has been around for 60K plus years (should be way more than 7 billion), and from only the 8 that came off Noah's Ark, you have a very plausible explanation for the 7 billion people on earth today. The differences in human 'races' are minor (skin color, shape of eye, nose, face, etc.), in reality we are all one race, one blood and can interbreed with no detriment to fertility. The distances in migration from the tower of Babel event is exactly as how God wanted us to spread across the globe in the first place and took place fairly quickly.

Truth Unites... and Divides said...

Hi Steve,

Thanks for the tip. I looked at the page on Snelling's book and it seems to concentrate on geology. Are there any web essays on Young Earth immigration?

For example, to get from Noah's Ark to Upper Russia through the Bering Straits down to California, from Asiatic to Eskimos to Native American Indians with various communities established, and moving on with harsh terrains and primitive modes of travel in a period of 6 to 10K years, it just makes me wonder.

It's not critical to my faith as a follower of Jesus; I'm just a curious guy.

Steve Drake said...

Hi Tuad,
Snelling's book not only addresses the geologic catastrophic past, but spends many chapters on just these types of arguments concerning the global Flood of Noah, the dispersions and migrations of both animals and mankind after they came off the Ark, but also the rapid speciation within the genetic variability of this very same biodiversity. It must be remembered, according to Snelling, that before the Flood, the earth was most likely one land mass, and post-Flood, during the Ice Age that followed the Flood and the eventual separation of the continents, there were still many land bridges between continents that are not there today. I'll see what I can find in terms of articles that address this for you.

turretinfan said...

"then think of the difficulties and distances of migration and the enormously quick micro-evolution which had to occur to obtain such differentiation between various races"

The migration patterns are an interesting question. The speed of migration can be greatly affected by whether people group predominantly hunts (potentially highly migratory like a number of the American Indian tribes), farms (tends to be quite stable, because cultivation pays dividends for staying in a particular location), fishes (tends to be fairly stable, since 'learning the river' pays, but can be predictably migratory, if the fishing supply gets exhausted in an area), ranches (generally nomadic to some extent), or raids (requires other nearby groups).

Various pressures (in addition to the food supply exhaustion one) can also lead to migration, particularly a desire for more arable land.


Steve Drake said...

Hi Tuad,
I think Snelling's book has the most comprehensive answer on this; it should also be remembered that Whitcomb and Morris' classic 'The Genesis Flood' also has a wealth of information on this question, but here's an article I found that you may find of interest:

A Possible post-Flood Human Migration Route

Steve Drake said...

Hi Tuad,
Here's the direct link in case you can't view the article:

Jonathan said...

Phenotypical distinctions between what we commonly call 'races' arise from genetic haplotypes that mutate and are redistributed as populations split/migrate, etc. It is not impossible to turn a single couple/family into a large population without significant deformities (though these would hamper population growth more frequently than with a larger initial population), but the modern diversity of haplotypes rules out the possibility of mankind originating from a single couple or family at any time in the past. Besides, human populations are well documented on multiple continents before, during, and after the time of Noah.

Perhaps we should reconsider the shallow exegetical approach that requires us to read Gen. 1–11 as a commentary on population dynamics, rather than as a prologue to history that elucidates the very nature of history, mankind, sin, judgement, redemption, etc.? However, my experience is that shallow exegesis and shallow science commonly go hand in hand.

Jonathan said...

"No, they don't." I didn't realize this was a valid argument. Should I respond with, "Yes, they do"?

"...assumptions about radioactivity present in the environment..." Do you know what those assumptions are? And do you know what methods are employed by geochronologists to verify that these assumptions are correct? What methods are used to constrain chronologies of human settlements that *don't* involve radiogenic isotopes? Do you know the difference between 'assumption' as it is used in the natural sciences versus common speech? Even if you'd like to dismiss their interpretations, you ought to be able to answer these questions that geochronologists/geoarcheologists address on a regular basis. Otherwise, you are (as I suspect) dismissing the evidence through ignorant conjecture. Regardless, unless you can provide a coherent interpretive framework to explain why radiocarbon, luminescence, cosmogenic, and U-series dates converge for Pleistocene/Holocene chronologies of sediments and artifacts, you have made a rather meaningless accusation.

"The historical nature of Genesis 1 is pretty readily apparent from passages like Genesis 5, which compares quite well with similar historical chronologies in Exodus." Sounds like you have 'founded' my point very well. 'Well it looks similar to other histories, so we must be able to read it like any other history written in modern time.' You still need to deal with the interpretive difficulties concomitant to ancient historiographies (particularly those from the Near East prior to Herodotus), and explain how the genealogical structure (a common literary device in ancient narratives) works literarily in conveying the narrative message. Your interpretation is reductionistic, but Genesis is quite polyphonic in terms of genre and its logic.

"No doubt you have plenty of experience with that." Yes, I do.

"Remarkably, no takers yet." I don't think many are aware of this challenge, but you don't seem interested in interacting with the bulk of modern scholarship on Genesis (even within Reformed circles). Hence, I don't see why this is remarkable.

Steve Drake said...

Interesting dialog. Not sure how to read the below three posts from Jonathan. Are you posting this, or is Jonathan, and was it dialog between you and he? Can't tell who's speaking what. With all the quotation marks it's hard to tell who's arguing what.

turretinfan said...

Steve: Generally, the bold bracketed stuff is mine. Anything else is what the original comment stated.

Steve Drake said...

Hi TF,
If Jonathan says this:
The *argument* is that a single family of eight plus ~4,300 years time (or, to be generous, 50,000 years) cannot account for the modern diversity of haplotypes and alleles within the human 'gene pool' unless we posit rates of mutation that are orders of magnitude larger than has ever been observed.

Then, respectfully, I would have to disagree. Scripture is clear. Only 8 humans survived the global, universal, cataclysmic judgment of God at the time of Noah. From what we can surmise from Scripture, this occurred c. 2350 BC. There is a variety of opinion concerning the haplotypes and alleles within the human gene pool. If Jonathan, then his side says no way this could have occurred in 4300 years. On the other side comes this:

Adam, Eve and Noah vs. Modern Genetics