Barriers to Evolution
From the thread "Genetic Barriers Don't Exist"
Post of the Month: July 2001
by Reed A. Cartwright
Subject: Genetic Barriers Don't Exist. Newsgroups: talk.origins Date: July 19, 2001 Author: Reed A. Cartwright Message-ID: sIN57.email@example.com
I've been reading some posts about the "genetic barrier" in another thread ("Thermodynamic challenge to creationists"). I figured I'd give the discussion its own thread. Now I know that some people will already know everything I say, but I'm saying it anyways. Perhaps someone will learn something.
I don't have the complete series of posts so I am unsure exactly what the "genetic barrier" is. I haven't seen any genetic evidence posted in the other thread to support such an idea. I also have never encountered such an idea before, and I am trained in genetics (BS in Genetics from UGA, currently studying for a PhD in Evolutionary Theory). All I can gather is that this barrier is proposed to "destroy" the foundation of evolution, but this barrier has no foundation of its own.
For starters, as I understand it, the genetic barrier hypothesis states, "there is a genetic barrier that prevents one *kind* from evolving into another *kind.*" I have yet to see any genetic, scientific justification for such a barrier. There clearly is not a justification because modern genetics has disproved this hypothesis. However, creationists still use the term because it allows them to look knowledgeable while actually knowing nothing. Such people have more negative ideas then positive ones.
The hypothesis of a "genetic barrier" was not originated by creationists. It arose almost a hundred years ago by biologists/evolutionists to describe the difference between macroevolution and microevolution. (For the sake of this argument, macroevolution is evolution appearing on the *super*-population level, and microevolution is evolution appearing on the *sub*-population level.) Creationists like to *claim* that the mechanisms from macroevolution are fundamentally different from the mechanisms for microevolution; this is their genetic barrier (from what I can tell). They then assert that there is no evidence for macroevolution while microevolution is well supported. They never show why any evidence supporting macro is wrong; they just say it is. A long quote (please forgive me) from Futuyma helps explains the issue:
"One of the most important tenets of the theory forged during the Evolutionary Synthesis of the 1930s and 1940s was that 'macroevolutionary' differences among organisms--those that distinguish higher taxa--arise from the accumulation of the same kinds of genetic differences that are found within species. Opponents of this point of view believed that 'macroevolution' is qualitatively different from 'microevolution' within a species, and is based on a totally different kind of genetic and developmental repatterning. The iconoclastic geneticist Richard Goldschmidt (1940), who held this opinion, believed that the evolution of species marks the break between 'microevolution' and 'macroevolution'--that there is a 'bridgeless gap' between species that cannot be understood in terms of the genetic variation within species. Genetic studies of species differences have decisively disproved Goldschmidt's claim. Differences between species in morphology, behavior, and the process that underlie reproductive isolation all have the same genetic properties as variation within species: they occupy consistent chromosomal positions, they may be polygenic or based on few genes, they may display additive, dominant, or epistatic effects, and they can in some instances be traced to specifiable differences in proteins or DNA nucleotide differences. The degree of reproductive isolation between populations, whether prezygotic or postzygotic, varies from little or none to complete. Thus, reproductive isolation, like the divergence of any other character, evolves in most cases by the gradual substitution of alleles in populations." (Evolutionary Biology, third edition. 477-478)
Barrierists believe, like Goldschmidt did, that macroevolution and
microevolution are fundamentally different; however, unlike Goldschmidt,
they use the absence of a macro-only mechanism as proof of a creator and
proof against evolution. The reason for the absence of a macro-only
mechanism is that the same mechanisms apply to both micro- and
macroevolution. This is not an *easy out* explanation as they'd have laymen
believe. It is backed up by genetic and biological observations and
experiments. Goldschmidt was able to state his claim in 1940 because the
science of molecular genetics did not exist then. It wasn't until the 1950s
that Watson and Crick solved the structure of DNA and showed how genetic
information was passed in cell division via template strands. The genetic
code was later solved, explaining how DNA encoded proteins. Modern
sequencing strategies allow us to map molecular genetic mutations to actual
genes, demonstrating the variability of populations and the power of
evolution. These sequencing strategies also allow us to map the differences
between two organisms' genomes. The genetic distinctions for taxa can be
detected by comparing organisms from different taxa. The data generated
from such investigations show that distinctions between taxa follow the same
rules as distinctions within a taxon.
**************************************** Reed A. Cartwright Graduate Student Department of Genetics University of Georgia "Real scientists don't have ministries."
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