Dear Straight Dope:
I was viewing the Straight Dope website and stumbled across a Mailbag article entitled "Does the theory of evolution fly in the face of facts?" SDStaff David states that there is constant evidence of animals being in a transitional state by evolution. This is true only in one way of looking at it, and SDStaff David fails to make the proper distinction that scientists have now made. Evolution as a theory was recently re-discussed by scientists as a body, and they broke it down in micro and macro evolution theories. As I am sure you are aware, macroevolution has more to do with the "common ancestor" aspects of evolutionary theory, whereas microevolution deals with the "survival of the fittest." As far as microevolution is concerned, it's hard to find fault with it. Even creationists, unless they feel particularly stubborn, will admit that it works. Macroevolution, on the other hand, is an entirely different story.
A. Frederic Harms
SDStaff DavidB replies:
All right! Creationists accept half the theory of evolution! We’ll have you guys believing we’re all monkeys’ uncles yet.
Let’s take a look at some terms. Creationists consider microevolution to be small changes within a species. A prime example is the often-cited case of the moths in England changing colors to blend in better with pollution-covered trees. The moth species stayed the same, but there were changes within that species. As you rightly note, Fred, this was an instance of survival of the fittest — the moths that blended in better with the trees were more likely to elude predators and thus pass along their coloring to their offspring.
Macroevolution is said to be the change from one species to another. This naturally leads to discussions beyond species and into genus, family, etc., and ultimately leads to the question of whether we humans share a common ancestor with apes. So you got that right too.
The problem is in your attempt to separate the two. Macroevolution, far from being “an entirely different story” from microevolution, is actually the same story, just on a larger scale. Creationists have not come up with a reasonable explanation why evolution should stop at the boundary of a species, rather than include the process that changes one species to another over time. Fact is, there is no such reason. No hard and fast distinction can be drawn between “micro” and “macro” evolution. It’s all one process.
A new book by Niles Eldredge (who co-authored the famous paper explaining the theory of punctuated equilibrium with now more well-known colleague Stephen Jay Gould) discusses this very topic, among many others. It’s called The Triumph of Evolution and the Failure of Creationism, and I encourage everybody to go out and buy a copy. Maybe two. Guys like this need all the support they can get.
One of Eldredge’s statements in the book summarizes the main point here: “There is utter continuity in evolutionary processes from the smallest scales (microevolution) up through the largest scales (macroevolution)” [p. 119].
Here are some of the other things he had to say on the microevolution/macroevolution topic:
Evolutionary processes taking place in relatively small scales of space and time connect to larger-scale entities, processes, and events to produce the entire history of life from the smallest incremental evolutionary change to the vast spectrum running from the simplest bacteria on up through the complex fungi, plants, and animals — from, in other words, the small-scale changes of so-called microevolution on up through the larger-scaled changes often referred to as macroevolution. This tremendously diverse array of life, spanning at least 3.5 billion years of Earth history, is all connected by a pattern of nested sets of genetic and anatomical similarity that can rationally be explained only as the simple outcome of a natural shared descent with modification [pp. 62-3].
Patterns of evolutionary change within species seem no different in principle just milder in degree from the sorts of changes we see between closely related species. All evolutionary changes are produced by natural selection working each generation on the variation presented to it [p. 76].
The evolution of a family should be no different in its basic nature, and should involve no different processes, from the evolution of a genus, since a family is nothing more than a collection of related genera. And genera are just collections of related species. The triumph of evolutionary biology in the 1930s and 1940s was the conclusion that the same principles of adaptive divergence just described — primarily the processes of mutation and natural selection- — going on within species, accumulate to produce the differences we see between closely related species — i.e., within genera. Q.E.D.: If adaptive modification within species explains the evolutionary differences between species within a genus, logically it must explain all the evolutionary change we see between families, orders, classes, phyla, and the kingdoms of life [emphasis in original, p. 76].
Microevolution and macroevolution differ only as a matter of scale, as we have seen from the connectedness of all life, and from the sliding scale of events — from the simplest, smallest evolutionary changes up through the enormous effects wrought as the aftermath of global mass extinctions [p. 88].
Creationists say there can be variation within kinds (microevolution) but not between kinds (macroevolution). Biologists assert that there has been one history of life: all life has descended from a single common ancestor; therefore one process — evolution — is responsible for the diversity we see [p. 123].
That pretty well sums it up. Granted, Eldredge is just stating his case here; I don’t expect the above to persuade you. (I’ll do that on the next go-round.) My point is that mainstream scientists, of whom Eldredge is a representative example, don’t attach the same importance to macro- vs. microevolution that creationists do.
Incidentally, as far as I know, there was no big conference of scientists on this topic (at least, none outside the realm of the creationists). I have no idea where you got this claim, but the terms macro- and microevolution were coined in 1927, casting doubt on the idea that this division is newly drawn. One would suppose that a guy like Eldredge would have been involved in such a scientific conference had it occurred.
In summary, it’s nice of creationists to admit that microevolution occurs, but the truth is that there is no magical dividing line between micro- and macroevolution. Biological evidence shows that changes within species are caused by the same natural forces that eventually cause differences between species, genera, families, and all the way up the line.
For further information on just what is or isn’t considered macro- or microevolution, see the Talk.Origins Macroevolution FAQ: http://www.talkorigins.org/faqs/mac roevolution.html.
SDStaff DavidB, Straight Dope Science Advisory Board
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