Didymus
Inactive Member
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Message 52 of 301 (68237)
11-21-2003 1:16 AM
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have introductory contribution, will travel.
Greetings to all present. I am brand spaking new to this board, and hope to lurk around and soak things up. I am in my third year of studying a degree in genetics and ecology, and I am a moderator of the evolution versus creation forum at Internet Infidels Discussion Board. For that forum, a few months ago, I composed this short piece looking at a few of the many different definitions of macroevolution. I repost it here with minor modifications for context.
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Macroevolution is easily one of the most heavily used but least understood terms in the public understanding of evolutionary biology. In the global creation/evolution debate as a whole, it is probably almost as commonly used a word as "it", "but", and "stupid". ... But does anyone know what it means? I used to think I did at one stage. Here, for example, I spoke of macroevolution:
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It's about the effect of large scale patterns on the course of evolution. It's about speciation, but it doesn't mean speciation specifically. It's also about the influence of ecological principles, geology, and still more advanced concepts than I think we even understand. It's NOT neccesarily about "one sort of thing changing into a different sort of thing".
This is PZ’s (a fellow moderator at IIDB, and a professor of developmental biology) take on the matter:
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It's just a term that describes a process that is currently the subject of active research, which contains phenomena that we don't entirely understand yet. I'll cite Gould here, in The Structure of Evolutionary Theory: I should be clear that I intend only the purely descriptive definition when I write "macroevolution" -- that is, a designation of evolutionary phenomenology from the origin of species on up, in contrast with evolutionary change within populations of a single species. In so doing, I follow Goldschmidt's own definitional preferences (1940) in the book that established his apostasy within the Modern Synthesis. Misunderstanding has arisen because, to some, the word "macroevolution" has implied a theoretical claim for distinct causes, particularly for nonstandard genetic mechanisms, that conflict with, or do not occur at, the microevolutionary level. But Goldschmidt--and I follow him here--urged a nonconfrontational definition that could stand as a neutral descriptor for a set of results that would then permit evolutionists to pose tough questions without prejudice: does macroevolutionary phenomenology demand unique macroevolutionary mechanics? Thus, in his book, "macroevolution" is descriptive higher-level phenomenology, not pugnacious anti-Darwinian interpretation. I think it is a useful term, and one that is going to become increasingly significant. Think of the difference between transmission genetics and population genetics: it's an extremely useful distinction, even though we don't imagine that special forces operate in populations that defy the rules of heredity for individuals.
RufusAtticus, another of our moderators whos area is population genetics, prefers this succinct definition:
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Evolution: The change of properties of populations of organisms over time.
Microevolution: Evolution apparent within species.
Macroevolution: Evolution apparent between species.
When I asked him to expand on that final line, he supplied this elucidation:
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That macroevolutionary differences are differences between species, nothing more, nothing less. The reason why I phrase it the way I do is to try to point out that microevolutionary differences and macroevolutionary differences are the result of the same process: evolution. The distinction between macroevolution and microevolution is an artifact of the history of our human investigation into biology. It does not reflect any real distinction present in the biological world. Paleontologists do often use "macroevolution" to refer to process of long-scale trends in the fossil record. But for the most part, biologists like me don't use it that way.
If the different perspectives I have seen offered up by three of this forums own moderators isn’t confusing enough, here are some more:
Talkorigins has this FAQ about what macroevolution is. It starts well, with this opening paragraph:
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In evolutionary biology today, macroevolution is used to refer to any evolutionary change at or above the level of species. It means the splitting of a species into two (speciation, or cladogenesis, from the Greek meaning "the origin of a branch") or the change of a species over time into another (anagenesis, not nowadays generally used). Any changes that occur at higher levels, such as the evolution of new families, phyla or genera, is also therefore macroevolution, but the term is not restricted to the origin of those higher taxa.
Punctuated equilibrium, Phyletic gradualism, Species selection and species sorting are all listed as examples of macroevolution. However, after a look at the history of the terms, the FAQ concludes with this:
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There is no difference between micro- and macroevolution except that genes between species usually diverge, while genes within species usually combine. The same processes that cause within-species evolution are responsible for above-species evolution
This appears to me at least to constitute a contradiction. I don’t see how punctuated equilibrium, a theory tied intimately to such broad fields as ecology and geography, can be said to be the result of the same processes as intra-species population genetics. If it is, what is the point of classifying it as distinctively ‘macro’? Again at talkorigins, The famous 29+ evidences for macroevolution FAQ contains another definition of the word in its introduction.
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Macroevolution, as used here, is the theory of descent by gradual modification from a common ancestor.
Here, it simply means common descent. Nothing more, nothing less. Perhaps it is a definition geared up to directly combat the creationist interpretation of the word, which is still more mutable itself. I have seen creationists define macroevolution as speciation, as common descent, as a crossing of the created kind barrier, as large-scale morphological change. There seem to be the ideas that the 29+ evidences FAQ is designed to deal with, but can macroevolution really be classified simply as ‘common descent’? If so, where does microevolution, something that no-one would claim is not involved in common descent, enter the picture? Some more, subtly different definitions from popular general biology texts:
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A major question in evolutionary theory is whether microevolution (the gradual changes that take place within species) can account for macroevolution (the diversity among families, orders, classes, and phyla). The process of speciation - the formation of new species-is considered of central importance in answering this question."
Curtis and Barnes, Biology, pg 1029. (emphasis mine)
Here, macroevolution is framed not as a process or a theory, but as a fact: something to be accounted for by either microevolution or some other process. This definition is the one that I most often return to.
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Macroevolution:
Evolutionary change on a grand scale, encompassing the origin of new taxonomic groups, evolutionary trends, adaptive radiation, and mass extinction.
Campbell, Biology, 6th Edition
In other words, macroevolution is practically everything in evolutionary biology that isn’t bounded in by a species barrier. Genetic drift: (the bottleneck effect, the founder effect) and natural selection: (gene flow, mutation) are possibly the only things excluded by this definition.
The main problem I have with the term ‘macroevolution’ is not with what it is, but with when it is used. As I have shown in this post, people of all walks of life are using this term for only one of its many meanings. When people mean anagenesis, they say ‘macroevolution’. When they mean cladogenesis, they say ‘macroevolution’. Common descent, paleontological patterns, origins of diversity, genesis of novel properties, are all specific aspects of the great evolutionary canopy, but all are frequently substituted for the single word ‘macroevolution’. It is my opinion that the worth of this term has been, and is being diminished by frantic overuse.
I strongly disagree with interpretations I have read in this thread that refer to speciation as a microevolutionary phenomenon. That does not gel with anything I have read on the topic. Thank you for listening, and it's nice to be here. [This message has been edited by Didymus, 11-21-2003]
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