Longtime readers will recall my ambivalence towards mendelian models of speciation:
Mendel is not enough
Mendel is REALLY not enough
Very briefly, the model posits that God created organisms with a fixed set of alleles (gene versions). As time went on and the populations began to spread out, certain combinations of alleles became fixed in certain populations, and those populations became species. As I wrote previously,
This model is still quite popular with creationists for what I consider to be mostly psychological or apologetic reasons: (1) It does not require the generation of new attributes or "genetic information" (whatever that is) after creation. (2) All changes can be perceived as degenerative, since the originally created heterozygous condition is broken up and disturbed as species separate out alleles from that original gene pool. (3) If you want to twist the definition of evolution, you can claim that speciation by this mechanism is "not evolution."As far as I can tell, Byron Nelson's "After its Kind", originally published in 1927, is the book that introduced this model to creationism. You can get a brief idea of Nelson's argument in the illustration of dog variation above. His view of biology is very similar to Frank Marsh's. Nelson accepted the idea of variation within certain created limits. Unlike Marsh, Nelson set out a very specific explanation of how those limits worked. In chapter four of "After its Kind", Nelson explained his mendelian ideas:
As the musician may combine notes into the making of new and peculiar harmonies, so nature, by making certain combinations of the factors [an old term for gene] existing in species, may produce occasional varieties new and strange to man.... Yet, no matter how strange such new varieties may seem, they are due only to a combination of factors already existing in the species. ... Each species, therefore, in the light cast upon it by the Mendelian discovery, is fixed and immutable. While variations occur, such variations take place within a closed system. ... A certain evolution, if one may care to call it so, occurs, but it is confined to definite limits set by the Creator. (pp. 109-111).Accompanying this chapter are various diagrams that illustrate the basics of dominant and recessive genes, mendelian ratios, incomplete dominance, and variations that might result from combinations of multiple genetic loci.
As I've said before, this model has become the standard explanation of variation among creationists. Given what Nelson knew at the time, his idea wasn't all that bad. Remember that mendelian genetics was still relatively new at the time "After its Kind" was published, in much the same way that genome sequencing is relatively new today. In the 1920, Nelson knew that this new science of genetics would require modification of creationist understanding of biology, and today, we know that genomics will require yet another revision of creationist models. Currently, genome science has shown that we need a significantly new model for understanding biological change from a creationist perspective. Whatever this new model looks like, we have creationist pioneer Byron Nelson to thank for that first marriage of creationism and genetics.
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