Macroevolution Vs Microevolution Arguments
June 26, 2013
There have been several Skeptoid posts over the last month that touched base with evolution and evolutionary theory. Several time the terms "Macroevolution" and "Microevolution" have been used by commentators articulating what I would term a denial of evolutionary science. These terms were used so much that I though it reasonable for focused review of what these arguments mean, and who uses it.
Microevolution Simplified: " Microevolution is a change in gene frequency within a population. Evolution at this scale can be observed over short periods of time — for example, between one generation and the next, the frequency of a gene for pesticide resistance in a population of crop pests increases. Such a change might come about because natural selection favored the gene, because the population received new immigrants carrying the gene, because some nonresistant genes mutated to the resistant version, or because of random genetic drift from one generation to the next."Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Despite their differences, evolution at both of these levels relies on the same, established mechanisms of evolutionary change.
A common argument/tactic for protesting the scientific veracity of evolution revolves around challenging one or both of these terms.
First of all they are terms not scientific processes or specific descriptions of processes. They are used by evolutionary biologists but they do not specifically describe any specific genetic or selective process. They are merely categories. Arguments using these terms often boil down to "A happens but B does not therefore evolution is wrong".
Words are not the master of science; science is, or should be, the master of its words. But we can inquire how scientists use their words, and whether they use them consistently. And having done that, we can inquire whether others who are not scientists read too much into them, or use them in a totally different way.
Here is good example of a Macroevolution argument from a prior post of mine.
"anonymous"-"Macro" refers to large changes in a population resulting in speciation, in which there are two kinds. One is caused by new genetic information in which a new species arises, and is the evolution that is disputed by creationists. The other form of macro evolution is speciation due to a loss of genetic data. A good example would be plant species that mutates, altering it's pollination time, preventing it from naturally pollinating within the general population. Micro evolution would be simple changes within a population that do not occur from new information, but simple mixing of information. Examples are differences between parents and their offspring, as well as different characteristics between ethnic groups of people or breeds of animals.Let's examine this argument in detail. What are the premises of the argument?
Evolutionary change requires informational increases in the genomes of organisms. Also that mutations are the only ways that this can happen (if other processes accounted for an increase, it would not be an argument against evolution). Plus, that mutations themselves cannot produce informational increase.
The first premise is not strictly true: evolution is defined as the adaptation of a population of organisms to its natural environment, and this does not necessarily require the information of the genome to increase. It can as easily decrease.
But, do point mutations cause informational increases in the genomes of organisms, like creationists say they don't? 100% correct, no, they don't.
Like many non-scientific thought processes this one revolves around a central speck of truth with false extrapolations caused by poor understanding of the discipline. Point mutations don't cause an increase in the individual genome's informational content, but rather in the population's gene pool as a whole. Changing one base pair in a genome does not change the informational content at all. The removal of one allele (gene variation) and replaced it with another. This ignores the fact that individuals do not evolve, populations do. A point mutation becomes the bringer of new genetic variation, which then can be pruned back with natural selection into a different population of organisms. Gene duplication is another mechanism that can increase of information in the gene pool and the genomes of individual organisms.
Gene duplication occurs when one gene is copied incorrectly and the organism gets two copies of the same gene in its genome. How does this relate to information increase? Point mutations changed one gene into an allele of itself. What if you had a point mutation in one of the copies, and the other remained the same? You would end up with the original gene and a variant of that gene, in the same organism. This results in a completely new gene. Given enough mutation voila evolution of a new gene. Transforming, biochemical pathways and transcription factors resulting in new expressed traits and subsequent selection.
Where are the examples? Most of these processes occurred in early earth history.
Life on Earth is at least 3.4 billion years old. Multicellular creatures first appear in the fossil record about 540 million years ago. That means that most of the history of life on Earth, about 3 billion years, was nothing but single-celled creatures. That is a very long time in which to evolve biochemical pathways and cellular complexity — more that 5 times as long as it took to get from a single cell to a person. Cells, proteins, RNA, organelles, and biochemical pathways do not fossilize. They are scantly preserved at all. We are therefore limited in our ability to reconstruct the evolutionary history of billions of years of evolution on this scale. Scientists only have a few methods available from which to infer the evolutionary history of cell structures and biochemical pathways. The main method is to look for patterns in living organisms. By analyzing thousands of species, they can partially reconstruct the evolutionary tree.
Perhaps the best method available is genetic analysis. Genes are a sort of fossil — they do record to some degree their evolutionary past. We can see when genes duplicated and then evolved to take on new functions. We can sometimes see inactivated genes, truly fossil genes, and infer past function from them.
That is why this part of evolutionary theory has been the focus of creationist arguments. New genetic information is a complicated, slow, time intensive process. It occurred primarily in early earth history, and has only limited examples now. Not zero examples just few examples.
There are current examples. Here are two.
Evolution can explain diversity in a limited number of created kinds which can interbreed (which they call "microevolution") while the formation of new "kinds" (which they call "macroevolution") is impossible. This is acceptance of "microevolution" only within a "kind".Essentially they are describing the same process. Although evolution beyond the species level results in beginning and ending generations which could not interbreed. Chromosomal changes can be explained by intermediate stages. A single chromosome divides in generational stages, or multiple chromosomes fuse. Examples of this are found in the human and comparative genetics of apes. Again not impossible, just difficult for lay persons to understand.
The last ditch denial argument is usually to point to a no-true Scotsman logical fallacy. A simple rendition of the fallacy would be:
Person A: "No Scotsman puts sugar on his porridge."
Person B: "I am Scottish, and I put sugar on my porridge."
Person A: "Then you are not a true Scotsman."
Any example of "Macroevolution" is broken down as not "true evolution". This is based upon the relatively arbitrary demarcation of what the term means. They redefine macroevolution as something that cannot be attained. Any observed evolutionary change as "just microevolution".
DanH: "All these examples of microevolution are fascinating. My particular favorite is the abundance of the Kermode black bear (called the Spirit Bear due its white color by the natives) in British Columbia.Even allowing for the misspelling clearly this a psudoscientific demarcation of a no true Scotsman fallacy. Only different chromosomal species qualify for "Macroevolution". That is not the definiton of Macroevolution. It is however a no true Scotsman fallacy.
In truth evolution within species is evolution. Just not the only kind. It is a trick that sounds good to lay persons but it false. For example bacterial plasmids will transmit antibiotic resistance to other bacteria. Sometimes across completely different species resulting in a new organism with a distinctly different genome. At one time there was no nylon on earth yet now we have nylon eating bacteria. Evolution. Only rapidly reproducing species produce current examples of mutation derived evolution. The more time involved the stronger the evidence. Most humans 7500 years ago did not have the ability to digest bovine milk. Now it is a common trait. Since genetics is a young science and evolutionary theory dictates significant time is necessary for mutation derived evolution, it is likely that examples are scarce. It does not refute the theory as a whole.
These arguments are a nonscientific use of scientific terms in an attempt to poke a hole in the total theory of evolution. This is a purposeful attack where the reproducible evidence is the weakest, and the science is the hardest for a lay person to understand. These arguments use scientific terms incorrectly to arbitrarily demarcate evolution into a more manageable target. This is because negating the whole of evolutionary evidence is impossible.
To disprove evolution you would have to disprove everything we know about.
Belief is not science it is just belief.
Griffiths, William M.; Miller, Jeffrey H.; Suzuki, David T.; Lewontin, Richard C.; Gelbart, eds. (2000). An Introduction to Genetic Analysis (7th ed.). New York: W. H. Freeman.
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