Sunday, November 4, 2012

Some ponderings on Darwin's views of domestic variation, showing again how the processes of evolution are naturally limited

In a copy of Darwin's Origin of Species that I have from 1979, a heavily abridged "coffee table" type book featuring lengthy commentary by Richard E. Leakey and lots of glossy pictures of animals, Leakey gives the following introduction to Chapter 3, Variation Under Domestication:
Darwin's idea that domestication can, in itself, cause greater variability to arise between individuals is now known to be wrong.  The greater varaibility which is seen in domesticated plants and animals is the result of their not having been subjected to natural selection which, if the environment is stable and the species well adapted, tends to eliminate those which depart from the norm.  Gene recombination and mutation are what give rise to variation, and these will occur at the same rate in the wild as under domestication.  But in the wild, variations will usually be far more ruthlessly weeded. out.
Thus goes the evolutionary explanation of 1979 and it sounds pretty familiar so I have no reason to think things have changed much if at all since then.  Of course he's right that Darwin was wrong to think domestication in itself causes greater variability than occurs in the wild, but his own explanation is just as wrong.  It's basically a recitation of The Creed, which is what an awful lot of evolutionist writing really comes down to.  "Not having been subjected to natural selection" is nothing but The Creed.  So is the inclusion of "mutation" in the explanation of what gives rise to variation.  Neither such drastic weeding by natural selection in the wild state, nor variation as the cause of such weeding, nor mutation as the basis for normal variation, is supported by actual evidence.  It's all speculative assertion.  The Creed.  Gene recombination, yes, that IS what gives rise to variation in both nature and under domestication, and yes, this WILL "occur at the same rate in the wild as under domesticatiom."  That much IS known for sure.

This topic particularly interests me because I've had my own explanation of how variation occurs for some time now, and it differs from both Darwin and Leakey's view, although it is quite compatible with some observations by evolutionists -- it just depends on which source you are reading. 

Darwin's discussions of variation, both in domestic plants and animals and in nature, are interesting because he had no knowledge whatever of genetics. Although Mendel was his contemporary, Mendel's studies of inheritance were not known until after both were dead.

So here's Darwin from this chapter:
When we compare the individuals of the same variety of our older cultivated plants and animals, one of the first points which strikes us is that they generally differ more from each other than do the individuals of any one species or variety in a state of nature.  And if we reflect on the vast diversity of the plants and animals which have been cultivated during all ages under the most different climates, we are driven to conclude that this greater variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from those to which the parent-species had been exposed under nature.  It seems clear that organic beings must be exposed during several generations to new conditions to cause any great amount of variation;  and that, when the organization has once begun to vary, it continues varying for many generations.  Our oldest cultivated plants, such as wheat, still yield new varieties;  our oldest domesticated animals are still capable of modification.
I'm sure breeders today could answer Darwin on this point if they were not brainwashed with the evolutionist notion of mutation as a major agent of change.  Genetic recombination explains it all quite nicely and all mutation does is interfere.  It may occasionally produce an unanticipated but benign anomaly (I'm not really convinced this happens though), and that could be exploited if one wanted it to be passed on, but it is hardly THE method that gives rise to variation, or even A method.

What brings about variation or change in the phenotype, change, that is, in the appearance or function of the creature itself, is REPRODUCTIVE ISOLATION.  Period.  Reproductive isolation simply means that a specific number of individuals of any species are separated from others of the same species and gathered together in an exclusive population of themselves alone, so that they only breed among themselves, and so that therefore their offspring carry only the genes and traits of the members of their relatively smallish circle, which over generations of such inbreeding can intermix all the genes/traits of all the original individuals so as to produce a very specific and unique appearance or set of traits that becomes characteristic of that overall population.  This is recognized in the field called Population Genetics but it gets confused with too many irrelevancies it seems to me and therefore isn't given the emphasis it deserves.  Natural Selection, which probably occurs to some extent but nowhere near the extent attributed to it, is just a form of reproductive isolation. 

Reproductive isolation is what happens under domestication, and it's THE reason for the development of a characteristic new breed.  Originally I'd suppose a portion of a wild species was brought under domestication, say of herd animals, cattle, sheep, goats or whatnot, some smallish number I would assume, or at least small compared to the original population, and the new domesticated population would then inbreed for generations until a new phenotype or particular set of traits would come to characterize the domesticated herd. 

This would occur over and over in different places as different portions of the wild herd were brought under domestication by different owners, or split between them so that they got isolated and inbred over time.  Their different gene pools eventually develop into separate herds each with its own characteristics that differentiate it from both the original wild herd and those of the other domesticated herds taken from that same wild herd.  This occurs over some number of generations of inbreeding.

THIS is why there are so many varieties of domesticated animals even when special breeding programs are not pursued, not Darwin's notion that somehow domestication itself produces variation, but simple reproductive isolation of a part of the original wild gene pool, which naturally occurs as part of that gene pool gets selected out for the purpose of domestication.  It's interesting to look up various animals on Wikipedia to get a list of the domestic breeds of each species.  Cows, pigs, sheep, goats -- there is an enormous number of varieties of each species.  Variation of course also happens in the wild but not nearly to such a dramatic extent as there is so much more intermingling of the individuals in larger populations, known as "gene flow" which is what DOESN'T happen with reproductive isolation.  Nothing to do with Leakey's affirmation of the Creed of Natural Selection as "weeding out" variations that arise.  The variation in nature is of course also due to reproductive isolation, which probably most often occurs through migration that leads to geographic separation of portions of a population from others, such as for instance the successive populations of ring species demonstrates.

It's nothing but reproductive isolation of the newer part from the older main population that brings about the many interesting differences between the different populations.  The smaller the new population and the more complete the isolation the more dramatic will be the differences. 

What's going on here GENETICALLY is that reproductive isolation of a small portion of the original gene pool brings about a CHANGE IN THE GENE FREQUENCIES in the new smaller gene pool (sometimes also the "parent" gene pool as well if it's not extremely large) so that new traits or phenotypes emerge in the new population as it inbreeds over some number of generations, mixing the new frequencies.  That's another well known principle of evolution. 

{Clarification:  Rereading this post (Wed Nov 7) I realize Darwin was thinking of variation among the INDIVIDUALS and I haven't said enough about that as I've been thinking of the amazing variety of BREEDS that occur under domestication and focusing on explaining that.  But I think an explanation of greater individual variation is implicit in the discussion in that the first few (how many?) generations of genetic recombination within the new herd or population would naturally turn up new traits among the various individuals because of the new gene frequencies in the population as a whole, and this individual variation should increase until at some point the gene pool starts to get more blended through continued inbreeding, and starts tending toward the establishment in all the individuals of the traits that eventually come to characterize the breed as a whole.   It's this final blending I've been thinking of as taking some number of generations to get established, but it's in those early generations that new variations would keep appearing as the new gene frequencies get played out.  I mean there are going to be fewer of some alleles and many more of others for many different genes so there will be more pairings that don't fit the blended trait picture of the original wild population, or whatever population was the parent.  I'm sure the word "blended" isn't the best but I don't think it's far off the mark of what must really happen.}

Founder Effect or Bottleneck are the most drastic examples of what happens genetically with the inbreeding of a new gene pool of new gene frequencies, although it happens in any isolated population that starts with smaller numbers than the original, it is just much more dramatic an effect when the population starts from extremely few individuals and has a drastically reduced gene pool that gets inbred.  Founder Effect or Bottleneck is when there are only a very few individuals that are the basis for the new population.  This has often happened in domestic breeding when a particular trait is sought and the elimination of types without that trait are carefully eliminated in favor of breeding only those that have the trait.  This has proved to have genetic drawbacks over time as it multiplies the opportunities for genetic diseases to occur in a drastically inbred population, but the principle is clear enough:  new phenotypes emerge to characterize a new population when competing phenotypes are kept from breeding with the desired breed or stock.

It seems to me that Darwin's observation that this occurs over generations is true and important.  It takes the inbreeding within the new gene pool to bring about a new reliable breed or variation.  How many generations this takes I don't know, but breeders may. 

I was reading up on some of the breeds of cattle and the Hereford is an interesting read.  Apparently it took a while to develop its characteristic appearance, at least a hundred years, its white face for instance.
Until the 18th century, the cattle of the Herefordshire area were similar to other cattle of southern England, being wholly red with a white switch, similar to the modern North Devon and Sussex breeds. During the 18th and early 19th centuries, other cattle (mainly Shorthorns) were used to create a new type of draught and beef cattle which at first varied in colour, different herds ranging from yellow to grey and light brown, and with varying amounts of white. However, by the end of the 18th century the white face characteristic of the modern breed was well established, and the modern colour was stabilised during the 19th century.[7]
Of course usually what breeders want is a breed that "breeds true," so that all the individuals born among the herd have the same characteristics.  Apparently this takes some number of generations to get established.

From other things I've read on this subject, for a breed to "breed true" means that there is a large proportion of genetic homozygosity in the gene pool for the breed's most desired characteristics.  This can happen in any population but again the most dramatic example of how it happens is the drastic bottleneck or founder effect.  A huge number of homozygous genes is characteristic of an inbred population that began with a very few individuals but again, the same condition can develop over successive population splits into new reproductively isolated populations.  It just gets there faster in the drastic cases, such as what happened with the cheetah and the elephant seal.  As long as they don't succumb to genetic disease they can be quite healthy and produce large populations but they lack the ability to vary further. 
Darwin's final line that many of the oldest domesticated varieties "are still capable ogf modification" suggests that they retain sufficient genetic variability, which really amounts to sufficient heterozygosity, to develop new varieties from further splits into new reproductively isolated populations and it suggests also that there is such a thing as reaching a point where further modification or variation ceases to be possible -- which occurs when there are a great many fixed loci or homozygous genes such as are possessed by the cheetah and the elephant seal.

A point IS reached eventually along any such line of continued "selection" of a relatively small portion of a population from a larger, and it must be reached if the process continues, where variation simply cannot occur further because of the great percentage of homozygosity, or lack of genetic variability, in the breed.

This is how EVOLUTION DEFEATS EVOLUTION, or in other words, how evolution comes to a screeching halt simply through the very processes that bring about the variations, or through evolution itself.  Variation can occur within a species, but that's all that is allowed by the laws of genetics built into the organism.  Simply due to the nature of genetics, Evolution Writ Large, or "macroevolution," or evolution/variation beyond the boundaries of the genome of a particular species CANNOT occur. 


Later:  Still rereading this post to try to clarify and correct and felt like adding this You Tube video of a wonderful breed of horses I only recently learned about, The KFPS Royal Friesian Horse, a horse with such an amazing natural elegance it's like something not born of this planet, truly a Royal breed, a heavenly breed even.

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