Microevolution vs Macroevolution
Is There A Difference Between Microevolution & Macroevolution?
By Austin Cline, About.com Guide
.See More About:evolution & sciencemicroevolution vs macroevolution
There is one particular aspect of evolution that needs to be given specific attention: the somewhat artificial distinction between what is called microevolution and macroevolution, two terms often used by creationists in their attempts to critique evolution and evolutionary theory.
Microevolution is used to refer to changes in the gene pool of a population over time which result in relatively small changes to the organisms in the population changes which would not result in the newer organisms being considered as different species. Examples of such microevolutionary changes would include a change in a species coloring or size.
Macroevolution, in contrast, is used to refer to changes in organisms which are significant enough that, over time, the newer organisms would be considered an entirely new species. In other words, the new organisms would be unable to mate with their ancestors, assuming we were able to bring them together.
You can frequently hear creationists argue they accept microevolution but not macroevolution one common way to put it is to say that dogs may change to become bigger or smaller, but they never become cats. Therefore, microevolution may occur within the dog species, but macroevolution never will.
There are a few problems with these terms, especially in the manner that creationists use them. The first is quite simply that when scientists do use the terms microevolution and macroevolution, they dont use them in the same way as creationists. The terms were first used in 1927 by the Russian entomologist Iurii Filipchenko in his book on evolution Variabilität und Variation. However, they remain in relatively limited use today. You can find them in some texts, including biology texts, but in general most biologists simply dont pay attention to them.
Why? Because for biologists, there is no relevant difference between microevolution and macroevolution. Both happen in the same way and for the same reasons, so there is no real reason to differentiate them. When biologists do use different terms, it is simply for descriptive reasons.
When creationists use the terms, however, it is for ontological reasons this means that they are trying to describe two fundamentally different processes. The essence of what constitutes microevolution is, for creationists, different from the essence of what constitutes macroevolution. Creationists act as if there is some magic line between microevolution and macroevolution, but no such line exists as far as science is concerned. Macroevolution is merely the result of a lot of microevolution over a long period of time.
In other words, creationists are appropriating scientific terminology which has specific and limited meaning, but they are using it in a broader and incorrect manner. This is a serious but unsurprising error creationists misuse scientific terminology on a regular basis.
A second problem with the creationist use of the terms microevolution and macroevolution is the fact that the definition of what constitutes a species is not consistently defined. This can complicate the boundaries which creationists claim exist between microevolution and macroevolution. After all, if one is going to claim that microevolution can never become macroevolution, it would be necessary to specify where the boundary is which supposedly cannot be crossed.
Conclusion:
Simply put, evolution is the result of changes in genetic code. The genes encode the basic characteristics a life form will have, and there is no known mechanism that would prevent small changes (microevolution) from ultimately resulting in macroevolution. While genes can vary significantly between different life forms, the basic mechanisms of operation and change in all genes are the same. If you find a creationist arguing that microevolution can occur but macroevolution cannot, simply ask them what biological or logical barriers prevent the former from becoming the latter and listen to the silence.
Microevolution vs Macroevolution: Is There A Difference Between Microevolution & Macroevolution?
Creationists like to erroneously claim that it is impossible for the
accumulation of microevolutionary changes to produce macroevolutionary
changes. A "genetic barrier" is oftern cited to account for this, although
it is never identified. The hypothesis states, "there is a 'genetic
barrier' that prevents one 'kind' from evolving into another 'kind.'" I have
yet to see any attempt to justify this hypothesis using actual genetics or
science. Furthermore, there clearly is not a justification because modern
genetics has disproved this hypothesis (see below). However, it is another
creationist buzzword that has no actual scientific value.
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, evolution apparent between species, and
microevolution, evolution apparent within a species. Creationists like to
claim that the mechanisms from macroevolution are fundamentally different
from the mechanisms for microevolution; this is their genetic barrier. 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:
<BLOCKQUOTE>quote:</font><HR>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)<HR></BLOCKQUOTE>
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.
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