Blinn

Anyone else?

From T.O.:
Yes, for example, we can say after the fact that the class Amphibia evolved from within the Osteichthyes, or that mammals evolved from the mammal-like reptiles, but the actual transitions occurred within populations, not class to class - our boxes.

This is why I believe that macroevolution is an abstract term (and shouldn't be used, nor should micro-). It applies to the nested groups of Linnaean classification but is not an actual phenomenon, since all evolution happens within populations.

The T.O. definition above calls even speciation "macroevolution," but I would bet most biologists still put that into the micro- category. Hell, even the creationists allow evolution of biodiversity from the "kinds" on the Fantasy Ark and call it microevolution.

"[B]etween-species evolution of genes"? Theoretically, a single base substitution could be enough to reproductively isolate, and initiate speciation. But I don't think that describes what most biologists would familiarly categorize as macroevolution. Hyla chrysocelis and H. versicolor (northern & southern gray tree frogs) are different species as a result of polyploidy but the only way to tell the two apart without a karyotype is by listening to the vocalization or taking a peek at the relative sizes of their erythrocytes. Although that fits the definition of macroevolution above, I wouldn't call it that.

I guess it depends on the observer. It's like looking at the visible light spectrum and trying to decide where orange ends and yellow begins. We can all definitely see the difference between red and blue, but red doesn't just switch to blue, there's a lot in between. Likewise, as you know, the fish class doesn't just change into the amphibian class, and that's why I don't like the differentiation.

In fact, I argued with a creationist one time that the terms microevolution and macroevolution were constructs of the creationists, not biologists. But then I went back to my intro. biology text (Biology, 2nd ed., Campbell) and sure enough, there they were-

Campbell’s definitions:

evolution: All changes that have transformed life on Earth from its earliest beginnings to the diversity that characterizes it today.

microevolution: A change in the gene pool of a population over successive generations. (this is the definition that I believe is most succinct and should be used for "evolution," sans macro- or micro-)

macroevolution: Evolutionary change on a grand scale, encompassing the origin of novel designs, evolutionary trends, adaptive radiation, and mass extinction.

That's my USD0.02.

(Note to barely literate creationists - I am not arguing about the factual event of evolution, just the nuances of how we describe it.)

RufusAtticus

Macroevolution versus microevolution harks back to debates in the thirties and forties over whether differences between species were of the same type as varation within a species. Of course, modern genetics decisevly showed that macroevolution was nothing but the accumulation of microevolution. I too have problems with making speciation synomous with macroevolution. I think it only confuses people who don't have much background in the field.

Here is something I wrote earlier.
<a href="http://www.talkorigins.org/origins/postmonth/jul01.html" target="_blank">Genetic Barriers Don't Exist</a>

~~RvFvS~~

[ July 02, 2002: Message edited by: RufusAtticus ]</p>

Dr.GH

RufusAtticus, Would you mind if I were to post a copy of your comments over here:

<a href="http://bbs.payableondeath.com/ubb/ultimatebb.php?ubb=forum;f=2" target="_blank">http://bbs.payableondeath.com/ubb/ultimatebb.php?ubb=forum;f=2</a>

RufusAtticus

Go right ahead. Just remember to put my name on it.

gallo

Then let me throw in my two cents too.

Starting from the bottom, I agree that the definition you got from Campbell should be, in fact is, the definition of evolution. I learned that many years ago and by god I'm going to cling to it forever! To be exact, I learned that evolution is a change in the allele frequency in a population over time. You can reword and expand various terms in that but it boils down to observable changes in the genetic diversity in groups of interbreeding organisms over generations.

But be clear. That is the definition of what constitutes the minimum process of evolution. It is a definition, not a statement of theory nor an explanation of a mechanism. It means that changes in individuals are not evolution, nor are changes that are not heritable.

But consider this case of speciation (macro-evolution?). In northern Europe and Great Britain there are two species of gulls that do not interbreed, even in captivity. They share a common range. The herring gull ranges to the west and the lesser black-backed gull ranges to the east. If you observe either population and follow its range to the east or west, you will find that you will circle the globe, end up back in northern Europe and Great Britain observing the opposite species. These gulls form a contiguous and continuously interbreeding population that circles the globe. But the at the extreme ends of its range, the accumulation of small genetic changes has formed different species. This is one of several ring species. It is a perfect example of multiple small genetic changes accumulating until a separate species is formed.

And yes, all evolution happens within populations. But what if a population (especially a small population) is isolated from the parent population? Is it not reasonable that it will evolve differently than the parent population? In the case I gave, the extreme ends of a single huge population were isolated by distance to the extent that they became different species. Polar bears are isolated from Kodiak bears by habitat - polar bears don't hunt in forests and Kodiaks don't roam the ice packs. There are even several striking and obvious morphological differences (fur, shape of face and head, feet, length of legs relative to body). But they are fully capable of interbreeding and producing fertile offspring. But if both survive mankind, it is doubtful that they will ever form a single population again in the future. Eventually, they won't be able to interbreed.

Consider also the hawthorne maggot fly. It infested (of course) the hawthorne. In the early 1800's apple trees were introduced to the Ohio valley. Since they were not native to the area there were few paracites. About 1850 it was noticed that flies that were identical in appearance to the hawthorne maggot fly were infesting apples! Since the hawthorne and the apple bloomed and fruited at different times, the maggot flies - although appearing identical - could not interbreed because their breeding cycle was congruent with the host plant. Since then, there have appeared the cherry maggot fly, and the pear maggot fly. I don't believe that they have jumped outside of the rose family of plants.

So imagine some primative reptile in a similar situation - pick any from above. You have two (or more) isolated populations that are prevented from interbreeding (by distance, breeding cycle, physical barrier). Now add millions of years where the same type of scenario occurs over and over. You end with reptiles, birds, dinosaurs, and mammals.

But all that said, I think that you do have a point. Through all of my studies of biology, including genetics and evolutionary biology, I never heard the terms macro/micro except in reference to Goldschmidt, his macromutations and hopeful monsters. That was a matter of the history of evolutionary theory. I was taken aback when I first heard the terms in a creationist debate - just like you. It seems that that the term macroevolution was coined to designate the result of one of Goldschmidt's macromutations. From there, came microevolution as a result of a mutation that caused only a slight change in morphology. I never liked the terms - I guess because I didn't learn them when I was a student. I have learned things since, rejected some and accepted others, but still to me evolution is evolution, continuous and ongoing.

But still, how many mutations caused the loss of pigmentation in the fur of a polar bear (they are black skinned, by the way)? I can't cite a reference, but I believe it is one. As a result, they can hunt on the ice pack. The rest comes as adaptations to the habitat. I could be wrong, but I don't think it is beyond reason.

So there you have my USD0.02. I never thought for an instant that you were doubting the reality of evolution.

Dr.GH

Naturally.

I thought that your presentation in a historical context would helpful to non-science kids.

Quetzal

I agree with everyone who dislikes the artificial distinction between micro- and macro-evolution. They're not even operationally very useful terms, IMO. Unfortunately, they now appear to be ingrained in the popular literature, and are starting to enter into the mainstream peer-reviewed articles. Even Ernst Mayr is guilty of using them - quite possibly the only quibble I've ever had with his works. He defines them in his popular science book, "What Evolution Is" as:

micro-: Evolution at or below the species level
macro-: Evolution above the species; the evolution of higher taxa and the production of evolutionary novelties, such as new structures.

He has a whole chapter (Chap. 10 Macroevolution) in the book regarding macroevolution. Maybe it's just an "evolution of language", but it appears to becoming an accepted distinction.

Is there justification - as Mayr, for example, seems to imply - for the use of two distinct terms in biology? I don't know. All I know is I don't like added complications - especially ones that play into the hands of the anti-science crowd.

Ergaster

I think there is, or has been, a discussion on TO about the inadequacy of the "macroevolution" FAQ.

Here is my perspective, FWIW: macroevolution *does* include change at the species level (this is from personal experience and education; for example, the university I attended offers a course called "Macroevolution" that deals basically with speciation, historical ecology, and cladistics).

However, the main problem with most attempts at defining macroevolution is that they fail to point out that macroevolution, while using the exact same *mechanisms* as microevolution, includes as part of its definition the observations of patterns of change over the long term (geologically-speaking, of course). It is true that the mechanisms of evolution only take place at the level of populations and species, and one of the reasons for this is that only populations and species are evolutionarily "real" units in nature--that is, you cannot have evolution at the genus or family level, because genera and families (etc.) are human constructs of taxonomic convenience, and do not exist in nature. Species that have diverged far enough from their sister-species over long enough periods of time generally tend to get classified into higher categories when humans observe them because they meet some sort of criteria of "difference".

So one of the requirements for macroevolution is time.

The other main difference is that there have been contingent and entirely unpredictable occurrances that, over the span of time, have profoundly influenced the pattern of life on earth and the origin and extinction of major taxa. These include mass extinctions, plate tectonics, natural disasters, changes in earth's tilt and oscillations which have profoundly influenced past cliamtes: all these things have had a huge impact on the way life has developed. Mass extinctions create enormous opportunities for the evolutionary radiation of survivors; tectonics divides populations, opens and closes migration routes among land masses, alters climates, and so on--I think you get the picture. The processes of microevolution are not different for macroevolution, but the temporal scale and historical circumstances decidedly have been.

That is why, IMO, there *is* a valid distinction between micro- and macroevolution, and why the standard explanations that try and either differentiate them or collapse one into the other are faulty. They are, at the very least, terribly incomplete. Macroevolution is about pattern, and this pattern has been influenced by events which do not occur or have the same kinds of long-term impacts at the level of microevolution, even though the processes of evolution are the same.

KC

Microevolution and macroevolution are relative terms only, denoting degree of divergence. They neither imply nor require a difference in mechanism.

Cheers,

KC

Blinn

If the macro- & micro- distinctions are going to stick around, IMO the following would be the most apt definitions:

Evolution Change in the gene pool of a population over time.

Macroevolution Evolution characterized by the divergence of gene pools between species or populations of a species.

Microevolution Evolution characterized by change in allele frequency of a population’s gene pool.