Ergaster

I was asked by Coragyps to copy part a post from another forum to here. I was responding to a poster who is, um, skeptical of evolution, let's say, and who is under the impression that macroevolution is a fantasy (gee...where have we heard that one before??). Here is my response:

<strong>"IF" [evolved] is a question only for cre/evo discussion boards. "IF" has not
been a scientific question for a very long time.

Are you still under the impression that microevolution and macroevolution are fundamentally different things? I believe I
addressed this some time ago--perhaps you have forgotten.

Speciation is often considered to be macroevolution, and for good reasons. However, they are somewhat technical, scientific reasons and thus, in order to fully understand them you will have to forget everything you ever heard about macroevolution from your creationist
sources.

Here are a couple of quotes from the scientific literature that may help you clarify your thinking.

"Evolutionary processes that occur at rates fast enough to be manifested as change within a single species lineage (*within-species* patterns) are included within the domain of *microevolution*. By contrast, processes that occur at slower rates, so that their effects are manifested in *among-species* patterns, are consigned to the realm of *macroevolution*. Microevolution and
macroevolution are thus considered to be parts of a more inclusive whole represented by the hierarchical nature of biological systems."

Brooks D & McLennan D. 1991. Phylogeny, Ecology, and Behavior: A Research Program in Comparative Biolgy. University of Chicago Press, p. 16 (emphasis in original).

"Nearly all the factors that have been used to distinguish the origin of higher categories can be attributed to the same processes of
speciation, behavioral adaptation and the gradual accumulation of morphological differences that characterize evolution at the levels of populations, species, and genera. There are no fundamental differences between the early stages in the radiation of placental mammals in the earliest Cenozoic and what is known to have occurred in the origin of the species flocks in the East African Great Lakes...Although formulation of a distinct theory of macroevolution does not appear to be justified, it may be convenient to retain the terms microevolution and macroevolution to describe the different patterns of evolution that are observed at the level of populations and species versus higher taxonomic levels and time spans exceeding 5-10 million years."

Carroll R. 1997. Conclusions and comparisons. In Patterns and Processes of Vertebrate Evolution. Cambridge University Press, p.392
(emphasis in original).

In other words, there is no difference in process between micro- and macroevolution. One describes populational evolution, the other describes the kinds of patterns that emerge when evolution carries on for a very long time (which should suggest the answer to your last question above...). Species are the only "real" taxonomic category in nature; anything above that (genus, family, order, etc.) are not found in nature, but are convenient organizational categories invented by humans. Once speciation occurs, and if the two species remain separated from each other, then they will evolve differently from each other. As time goes by, they will become increasingly
differentiated. In terms of the time scale of the earth, humans have only been around long enough to have observed the tiniest slice of time. If we happen to observe two species who have recently diverged, we see how similar they are to each other and categorize them by placing them into the same genus. If, however, we observe two species that diverged long ago in the distant past, we see that while they might retain some very basic similarities to each other, they are
much too different to belong in the same genera and so we place each into a higher category: family, or order, perhaps, depending on our
criteria of "difference" for that organism. In other words, the regular mechanisms of evolution (see the second quote above) continue to work in each lineage, but over great amounts of time certain patterns emerge among various lineages. Macroevolution is the description and quantification of these patterns.

So, yes--given that the main difference between micro- and macroevolution is time, humans are exceedingly unlikely to be able to observe this gradual divergence of lineages.</strong>

As an additional note: I would highly recommend the Carroll book, and suggest that everyone have a copy of that last chapter at least(referenced above) for their files. He summarizes a whole whack of information about macroevolution in it; I could easily have quoted the whole shebang!

Doubting Didymus

I don't even understand why we keep the terms. there is no such thing ans 'micro' and 'macro' evolution. Its all the same evolution, at similar speeds.

The terms aren't even convenient, they are misleading at best, creationist fodder at worst. We already have a term for the only 'above the species level' evolution that exists: speciation.

Coragyps

Thanks, Ergaster!

Blinn

I agree. <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=58&t=001015" target="_blank">Here</a>
is a thread I started earlier on the subject. Obviously, we biologists seem to differ on whether speciation is micro- or macro- evolution. Maybe that just makes the point the the terms are ambiguous. "Macro-", if I must use it, is differentiation somewhere at about the class level, IMHO. Anyone want to suggest definitions based on genetics?

[ July 29, 2002: Message edited by: Zetek ]</p>

Ergaster

I have to disagree, and for a couple of reasons.

First, it is simply a fact that the normal processes of evolution alone could not have produced the history of life as we currently observe it. There are events that occur during the time frame required for macroevolution that contribute to these historical patterns emerging: things like mass extinctions (the opening up of new possibilites for surviving lineages with resulting great radiations of new forms), plate tectonics (shifting continents contribute to extinctions, also open up and close migration routes, shallow contintal shelves), catastrophic events (asteroids, massive volcanic eruptions which cause differential extinction and survival quite independently of the mechanisms of microevolution)--all these things cannot be disregarded in the production of the patterns of life as we know it. They will continue to influence the future trajectory of life. Microevolution, understood as process, and macroevolution, understood as the result of these and external processes in producing patterns over the long term, are indeed very useful terms. Macroevolution simply is not "microevolution writ large". "Macroevolution" connotes external influences as well as normal evolutionary mechanisms.

Secondly, I reject the notion that we must abandon a useful term just because creationists might subvert and misuse it. If we do so, then they have won a small but significant point in the game. Our aim should be to educate people about the proper use and meaning of terms, not give up because creationsits are scientifically clueless and agenda-driven and we get tired of correcting them again and again and again.

"Macroevolution" is a term that many biologists use. They are not "wrong" because creationists don't understand it. We keep insisting that creationsim is a political, not a scientific phenomenon. If that is true, we cannot discard useful scientific concepts because of them, or go about whispering in corners because of the possibility that they might overhear and misuse our words. In the realm of science, we must concede nothing to them.

gallo

That sounds good, Ergaster, but what we observe is that a tetrapod always gives birth to a tetrapod and never an arthropod.

pangloss

A very oversimplified take on the micro-macro thing:

Morphologists in general still believe that there is a substantive difference between 'micro' and 'macro' (Mayr, for example)

Geneticists in general believe that 'macro' is 'micro' writ large


LOTS of overlap and disagreement....

Ergaster

You tetrapod, you!

scigirl

Ergaster,

Excellent post. It always makes me sad to see talented scientists (like us ) wasting so much time convincing people that the scientific method is a better way to examine life than reading ancient mythology. Imagine how much more we would understand about micro and macroevolution - how extinctions and disasters play a role, what types of genetic mutations are required, etc - if more people would just accept the theory in the first place!

scigirl

Blinn

The problem with the term 'macroevolution' is that it is often used in two different senses, one being "speciation" and the other being "evolutionary change on a grand scale, encompassing the origin of novel designs, evolutionary trends, adaptive radiation, and mass extinction" (Campbell 2nd ed.).

It seems that most people on this board use the first definition. Speciation doesn't require grandiose change, and as DD pointed out, why call speciation 'macroevolution' when 'speciation' suffices?

And since higher taxa are not natural units but rather constructs of convenience, using 'macroevolution' to refer the evolution of higher taxa seems to imply a process that in reality doesn't exist. All evolution is in populations. Nothing macro- about it. Ditch the terms.