JB01

We’ve all seen versions of the following argument played out ad nauseam in debates with creationists; we must have seen it rehashed dozens of times on this forum alone:

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Educated Person: Evolution, by definition, is simply a change over time in allele frequencies within the gene pool of a population. This is observed happening all the time. One of the mechanisms of this change is the fact that some heritable traits tend to cause their possessors to produce more offspring than those who lack the trait, for example by making them more likely to survive to a reproductive age or by making them more fertile. Since the trait is heritable, the offspring are likely to have it too, and the frequency of the genes that confer it will increase. This is Darwinian selection, which is based on known processes and simple logic, and it too is observed happening all the time.

Creationist: But that’s just microevolution! We already agree that that happens. It lets species adapt to new environments, but it can’t turn one kind into another.

EP: What exactly is a “kind”, and what is this mystical barrier that prevents one from changing to another? A future paleontologist who dug up the bones of a Great Dane and a Chihuahua would be justified in concluding that they were different species, but we know that they were both arrived at by successive selection from a single common ancestral wolf-like species.

C: But they’re still dogs!

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Now I’m not a biologist – I’m a physicist – so this may be presumptuous of me, but having read a lot on the subject, I have some ideas about how biological terminology may be contributing to this confusion.

The creationist in the imaginary debate above has one idea more or less right, which is that evolution proceeds by diversification within a lineage, never by transmogrification across them. That of course is why all known life fits so neatly into the nested hierarchy that allowed Linnaeus to slot it all into his taxonomic system even before the significance of the hierarchy – the unmistakable evidence it provides of common descent – was realized.

Each taxon in the series kingdom-phylum-class-order-family-genus-species represents a branching event within the next-higher taxon. From this it follows that the position of a classification within the hierarchy reflects an approximate, non-absolute measure of how long ago the branching occurred, relative to the present. The only difference between a phylum and a family is that the latter branching happened much more recently; in both cases the branching had to begin as two different species within a single genus of their respective eras. (This is why the “sudden” appearance of so many modern “phyla” [from today’s perspective] in the Cambrian explosion should not be surprising).

So we should be prepared to concede to creationists, that yes, anything descended from a dog will still be a dog, in the same sense that birds are still dinosaurs and humans are still mammals. But in the unlikely event that human and dog lineages both survive for tens of millions of more years, our descendants will almost certainly have to add quite a few new levels of taxa below the seven listed above, and “dog” will not represent a single species but an entire category of animals with virtually nothing in common in terms of appearance, size, behavior, diet, or environmental niche aside from a few residual traits to serve as evidence of their common ancestry.

My main point is that the standard Linnaean categories are an attempt to slap a few crude guideposts onto the incredibly complex branching structure that is the tree of life. If biologists made a greater effort to do justice to this aspect of their worldview in expounding evolutionary theory to the ignorant, it might help to forestall at least one type of frequent misunderstanding. I doubt this would make much headway against dogmatic biblical literalists, but it might at least help to clarify the discussion a little.

theyeti

I think you're right on. The creationist argument "it's still a dog" is nothing more than a semantic game that confuses the issue. More importantly, it's the effect of them sticking to their presuppositions about some magic barrier between "micor" and "macro" evolution. When pressed about it, they will never elucidate what exactly a "kind" is in any meaniful way, nor why enough divergence between lineages will never result in separate kinds. By far the most irritating thing about debating creationists is that their arguments are 90% rhetoric that have little to do with biology or evolutionary theory.

theyeti

Quetzal

JB01: I think you're on to something here. I'll try your approach during my next encounter, and let you know how it turns out. Obviously, I don't hold out tremendous hope - but I've always been an incurable optimist.

Grumpy

It's hard to believe that organisms, in all their variety, were not rolled off an assembly line like models of cars. Each one conforms to a prototypical form. Sure, there may be some varieties based on model year, but a Ford Fairlane is still a Ford Fairlane.

Yes, you can point to models of cars which appear in successive years and see, for example, tail fins grow and then shrink. But these are not direct descendants; rather, they are each individually designed and manufactured.

I can even prove that cars didn't evolve: They contain irreducibly complex parts! Take gas stations. What purpose would they have served before cars were invented? And how could anyone drive the first car (very far) before there were gas stations? It must have all been Intelligently Designed.

(But, you say, if the Designer was just as intelligent in the past as today, why don't we see modern forms of cars in the automotive "fossil record." It's almost as though cars, like organisms, change not through directed deliberation, but as accidents of historical contingency. But now I'm just thinking out loud.)

The Lone Ranger

Personally, I'd like to abandon the word "theory" in science, though I don't know what to replace it with.

It's so frustrating to keep telling people -- over and over and over again -- that "theory" doesn't mean the same in science that it does in everyday usage. I think that we could clear up some of the misunderstanding of science that permeates the general public if we'd stop using "theory" to describe our understanding of things like the evolutionary process.

Cheers,

Michael

[ January 28, 2002: Message edited by: The Lone Ranger ]</p>

Quetzal

Grumpy: LOL!

"why don't we see modern forms of cars in the automotive "fossil record."" OF COURSE there are transitional car forms in the record! Ever been to a junkyard?

Dr.GH

The following link is to a very good discussion of the notion of species. Some of our confusion about the meaning of terms can make it difficult to explain them to others.

<a href="http://www.aaas.org/spp/dser/evolution/science/mayr.htm" target="_blank">http://www.aaas.org/spp/dser/evolution/science/mayr.htm</a>

Late_Cretaceous

This kind of confusion is common in the kingdom/phylum/class heirarchy. How can a turtle and an alligator both be reptiles, when an alligator is much much more closely related to a chicken then a turtle. Usind cladistics, the degree of relatedness is reflected, also you dont stop being what your ancestors were. In other words, we are still cynodonts - even though the first cynodonts were mammal-like reptiles. Birds and alligators are both archosaurs, not separate groups.

Peez

I agree with you in as far as the misuse of the word "theory" is frustrating, but the scientific use of the term is not obscure. In fact, it is the first definition in my Webster's dictionary. In addition, the common descent of living things on this planet is not the theory of evolution. The theory of evolution explains the fact of common descent. Unfortunately, I see little hope in getting many creationists to see this, but explaining the distinction between the fact of evolution (common descent) and the theory of evolution (mutation, genetic drift, and natural selection) is certainly worthwhile.

Peez