Volume 10, Number 2

The Role of Natural Selection in Macroevolution Theory

Web note: Origins Research Fall/Winter 1986 (9:2) and Origins Research Spring Summer 1986 (10:1) are not yet available on-line, however we anticipate their arrival in the near future. When these issues become available on this site, we will create a link between this dialogue and the previous two.

Following is round two of a dialogue between Arthur LaGrange Battson III and J. Richard Wakefield on the role of natural selection in evolutionary process. Battson opened the dialogue in the Fall/Winter 1986 issue of Origins Research (9:2) with an article entitled "The Paradox of Natural Selection." Battson suggested that natural selection works to inhibit major evolutionary change resulting in stasis.

In the last issue of Origins Research (10:1), Wakefield responded that Battson's thesis was only correct in a stable environment. Wakefield claimed that earth's history is full of unstable events (such as plate tectonics) which would produce macroevolutionary changes with the help of natural selection.

Battson replied in the same issue that plate tectonics is a slow and gradual process and not a sudden unstable condition. Battson pointed out that no new phyla have arisen over the past 500 million years of drifting and buckling continents. He reiterated that any theory of origins must account for the two key features of the fossil evidence: stasis and the lack of transitional forms among the higher taxa.

And now for round two.

Directional Selection

Wakefield: I'm so glad to see that Arthur LaGrange Battson III is willing to accept plate tectonics. This cannot be said for many other creationists though who flatly refuse to accept this great scientific idea, second only to Darwin.

I would like to address some of the points Battson referred to in his response to my previous letter. He is not totally correct to say that natural selection tends to keep populations in stasis. This is the case in a stable environment. But stasis is not necessarily the case even in a stable environment. Predator/prey relationships can select populations to change (for example, "progress" towards faster running) in spite of a stable environment.

Battson: There was never any question as to the fact of directional selection. The example of the nut and seed eating birds in my original article shows directional selection taking place in a stable environment. The shift from point C to point D is the result of genetic change coupled with directional selection and is a good hypothetical case of microevolution. The original article by Roger Lewin on which the example was based (Science v.231 14Feb1986 p.673) explained how natural selection can inhibit gradualism in a stable environment and predict a pattern of punctuated equilibria:

"But", Lewin points out "the debate began with the challenge of explaining the punctuated equilibrium pattern -- and specifically stasis -- in the face of a changing environment. This remains to be explained to the satisfaction of all sides."

My point in the reply to your previous letter was that environmental change is an insufficient cause to produce macroevolutionary change. Apparently, environmental change is not even a sufficient cause to always produce microevolutionary change

Natural Selection as a Constraint

Wakefield: Natural selection is like a small multi-dimensional (one dimension for each selective pressure) window which not everyone can get through. If you are the lucky one with all the attributes to get through that window then you get, on average, to reproduce. It is here that we have the constraint. However, when the environment changes the window shifts to another position (if it shifts too far the whole population will become extinct.) Now a new set of constraints are imposed on that population and now a different set of attributes in the population are required to reproduce. The descendents of the population over time will have to become different (Darwin's descent with modification).

Battson: Your description of natural selection is a good one. Basically it is a constraint rather than a creative mechanism which eliminates the less fit from a population (if not the entire population, as you point out). It should never be thought of as a creative mechanism because it is obvious that nature cannot "select" anything that doesn't already exist.

The Naming of a New Species

Wakefield: Now is this the same species, or is it a new one? How long does change have to "progress" in a given direction before you would be forced to rename the population a new species? You can't use the same name as the parent population which gave rise to the new population.

Battson: Technically a new species arises when a population becomes reproductively isolated. When reproductive isolation cannot be used as a criterion, as is the case with fossil species or asexually reproducing species, morphological differences may be used to classify new species.

Competition and Adaptation

Wakefield: However, leaving the environmental pressures on populations and sticking with pressures between populations we can clearly see cases of apparent progressive change. This progressive change is an added burden to the environmental pressures. This is so true in the selection for mimicry in insects, for example the eye spots on moths.

How have these organisms been formed to mimic so well something they are not? Because of the pressure of another organism (like a bird) selecting as food those individuals which do not look what they are. As the mimic becomes closer to something else in appearance by the predator, members in the predator population are selected for those who are better at detecting the deception. The birds are selecting better eye mimic moths, while in turn selecting themselves as better seeing birds. The end result of this out of control mutual selection is perfect eye mimics, and excellent seeing birds. Apparent progressive evolution, by natural selection, is achieved because of the interactions between populations in competition with each other, or for each other.

Battson: If the adaptations already exist in the population, competition can act to increase their relative numbers. Competition can also act to prevent the loss of adaptations and the deterioration of species. However, when it comes to major evolutionary change, competition can act to prevent the establishment of novel new body plans. Any novelty which arises rapidly by essentially non-selective processes is likely to be poorly adapted, the consequence being that the more novel the bauplan the more adaptive space (i.e. less competition) will be required to permit it to become established.

Phyla versus Species

Wakefield: There seems to be some confusion over the origin of the higher taxa. Natural selection does not operate at any taxonomic level except at the level of the individual in a population. The higher taxa are a consequence of the accumulation of speciation events over millions of years. To say phyla evolve is totally incorrect. Phyla do not and can not evolve, only the species within the phyla evolve because of the selection of certain numbers in that species.

Battson: Evolution must certainly begin with a single individual of a species. Novelty must arise before there is anything to select. When selection of drift takes place populations "evolve" only in the sense of a relative increase or decrease in the number of those individuals. Don't be too quick to throw out selection above the individual, however. Punctual change is thought to occur through species selection.

The origin of a new phylum requires the origin of a new species so different that it cannot be classified in the same genus or family as its parent species; so radically different, in fact, that it cannot be classified in the same order, class or even phylum. The morphological differences between the phyla are profound, the body plans so radically different that we should expect: 1) clear evidence of transitional sequences if evolution occurs through the accumulation of microevolutionary events; and 2) immense time spans between the appearance of new pyla. The fossil evidence as was pointed out in the original article gives us neither. The argument put forth was that the incipient stages between major body plans would be poorly adapted and hence would be eliminated by natural selection. This would prevent the accumulation of minor changes that lead to the origin of a chain of species leading to a new phylum. For the sake of brevity it can be said that natural selection inhibits the evolution of new phyla while fully understanding that selection is acting against individuals poorly adapted to their environment.

No New Phyla

Wakefield: Battson is correct in pointing out that over the past 500 million years no new phyla have arisen, and that we have even fewer phyla now. Actually, with his view of creation, that question is really more appropriate to ask the creationists. Why did God only create phyla 500 million years ago? Why did He not create a new phyla 3 million years ago? No new phyla is what we would expect. But why is that? Stephen Jay Gould answered that in a Nova program he did a few years ago.

"If you look back 500 million years ago, early history of invertebrates, there was an enormous range of designs which we no longer see on the Earth. Designs which we don't even know how how to relate to any existing groups, because any pattern in the history of life it's not progressive advancement of complexity. It's rather the restriction of these enormously varied designs that existed early in the history of life to a few highly successful forms."

This is the whole point of the origin of new taxa, the restriction of a large group of varied populations to just a few which in turn give rise to more large groups of varied populations. Though it is not really proper to think this but a taxonomic level, such as phyla and class, could be seen as a moment in time where a major event occurred to restrict the populations then to just a few. That time measure is from our perspective, and backwards with respect to the direction of time.

Battson: Your question regarding God's creative activity is beyond the knowledge of this author and beyond the scope of science to answer.

No new phyla is what an evolutionist would expect? Is evolution merely the subdivision of pre-existing designs into reproductively isolated subtypes and the extinction of "enormously varied designs"? Admittedly that may be all that natural processes do, but evolution must be able to account for those enormously varied designs in the first place.

Traveling Back in Time

Wakefield: If we were to be able to go back to 500 million years ago and classify the life forms we would have no trouble making species, genera, and families out of the populations. But would we be able to make any higher taxa with these groups? I don't think so.

Battson: I must disagree. Actually there was much less diversity among the lower taxa and much greater diversity (novelty) among the higher (an enormous range of designs as Gould put it). It is a possibility that we would have had fewer taxonomic categories but those categories would not be missing at the top. As diversity increased through time it did not become necessary to create additional higher taxa or even increase the number of phyla (or whatever you wanted to call them) but rather add to the number of subgroups. If we were to travel back to the early Cambrian, chances are we would classify its life forms into well over 100 phyla and the idea that these enormously varied designs shared a common ancestor would probably be the farthest thing from our minds. The idea of common ancestry is basically an extrapolation of the common ancestry of very similar species in our modern world of tremendous species diversity. There comes a point, however, where the extrapolation to link increasingly diverse groups goes well beyond the data, and, in my opinion, beyond reason.

I have chosen the level of the phyla to test for common or separate ancestry for two reasons. First, the differences between species classified in different phyla are tremendous and hence ought to offer us the greatest number of transitional sequences between them to establish common ancestry. Second, the level of the phyla gives us a better view of the whole life than would selected examples of relatively minor change at lower levels.

Once criteria are set to determine the common or separate ancestry of the phyla, we can proceed systematically down the taxa to test for common ancestry among classes, etc.

Diversity through Time

Wakefield: Though most of these current populations will become extinct, a few of these current populations will one day (500 million years later) give arise to a whole new set of life forms. Then these few forms which survive will become the past representatives of the "phyla" they propagated.

Battson: Diversity at the species and genus level will certainly increase through time but that is not the problem. The problem for evolution is accounting for the species which existed 500 million years ago which we classify in different phyla.

Age of the Mammals

Wakefield: Later mass extinctions, with a surviving few, gave rise to other lower taxa. Mammals are a classic case. The first "mammal" population 225 million years ago was only a population and would have been given a species name. But since the Cretaceous/Tertiary extinctions a whole new radiation of life forms exploded to become the "class" Mammalia. That class was "born'" so to speak, 65 million years ago. Families within that class were "born" at times during the age of Mammals.

Battson: The first mammal population would have been placed in the phylum cordata the subphylum vertebrata and would have been given its own class, mammalia, because it did not fit within any of the existing classes of the subphylum vertebrata. Admittedly it would have been the only member of this class. Many taxonomists insist that the species name always include the genus name even though no other species may exist in the genus. Such is the case for us. As Homo sapiens we are members of the only species within the genus Homo. There is even a phylum that is represented by a single species. It is designated in a new phylum because it does not share characteristics found in any other phylum. Apart from giving it a traditional name, however, there is no need to tag it with class, order, and family labels until there are additional members of the phylum.

Classy Penguins

Wakefield: Would you classify penguins as a separate class today? No, they are birds. But look 100 million years from now at what the penguins might become, especially if major niches open up because of a mass extinction which they survive. In that time, when they have moved into the open niches and diversified, they would be put into a class of their own.

Battson: If they lost their feathers they would no longer flock together (at least in the class Aves.)

Mass Extinction

Wakefield: Imagine a mass extinction today and only a few life forms (say from one class) surviving. Those few forms, over millions of years, will give rise to who knows what types of life forms. In 500 million years from now, some intelligent life form will try and classify their present biota. With an added 500 million years of evolutionary change, they will have to have one heck of a taxonomic classification system, with far more levels than we have. The level of phyla to them might be 1987 because all their forms came from a few highly successful forms which survived the 1987 mass extinction. They then would have the same problem of classifying all the forms which did not survive.

We must remember that the taxonomic hierarchy is artificial, and really only a tool for our convenience. Only species evolve, the other taxa are a consequence of the diversity certain originating species have become over time.

Battson: At the lower taxa we agree. However, I am not at all convinced that species which are classified in separate phyla ever shared a common ancestor.

God of the Gaps

Wakefield: So much for the origin of the higher taxa. Another item must be brought up. Unfortunately, Battson has fallen into the God-of-the-gaps hole with his last comment of "I have concluded that [creation] is a logical inference based primarily upon the lack of adequate evolutionary mechanisms ..." (emphasis mine). The lack of data on anything does not implicitly imply anything! Nothing can be deduced from a lack of information. It must be left open, as an unknown. I have confidence that the solutions will yet be forthcoming.

Battson: Oops! I certainly did fall into that age old trap. Now excuse me while I crawl out of it and dust myself off.

What I should have said was given the immensity of the Cambrian explosion, the short period of time in which nearly all phyla appeared, the lack of transitional forms among the higher taxa, the geological evidence for stasis, the pattern for the origin of the higher taxa, and particularly the tendency for natural selection to inhibit major evolutionary change, it is quite logical to conclude that all life did not originate from a common ancestor but has descended instead from a number of basic body plans. It is not the lack of an evolutionary mechanism as much as it is the existence of natural processes that inhibit major evolutionary change from occurring, and which account for the natural phenomenon of "macrostasis." It is not what we don't know, but rather what we do, that makes the inference of creation logical to me. Are there other natural processes which account for stasis and inhibit evolution? Undoubtedly there are and I have confidence that additional answers will yet be forthcoming. Very few scientists over the past 130 years have even thought of developing a theory of macrostasis. If the theory more accurately describes processes that actually occur in nature we should be hearing more of it - unless, of course, we continue to insist that the origin of all biological diversity must be the result of purely natural phenomena or that all life on earth must share a common ancestor.

The Final Challenge

Wakefield: Some creationists claim that scientific research into these areas, like the origin of the higher taxa and the origin of life, is futile and a total waste of time because these were supernatural events. If in our historical past we had listened to that same argument we would still be believing in a flat earth at the center of the solar system and dinosaur fossils are the deception of Satan!

I see that Battson did not address my last questions, which other creationists have likewise dodged. It is fine to scrutinize evolution. We have no fears of that - it is what makes us stronger. However, I'm turning the table around. I'm challenging any creationist who answers this letter to come up with a mechanism for creation from nothing. No, on second thought, I am demanding creationists clarify this very important point. I don't buy the argument that it is supernatural and hence cannot be the subject of science. Hogwash! This creation event manifested itself into reality (some say over geological time). HOW? What are you going to say to school children who ask the same questions? Probably, tell them the answer is "out-of-bounds" and "Do not question!".

Battson: I can only repeat my opinion that creation events are by definition non-natural events and hence are not subject to scientific investigation.

With regard to origins and the ultimate creation events listen to what the authors of Biology, Villee, Solomon and Davis, have to say:

"As critics, the creationists remind us that the theory of evolution is indeed a theory, subject and in need of much scrutiny and reevaluation. As scientists, however, the creationists offer us an alternative to evolution that amounts to an unfalsifiable hypothesis. For in the study of macro- and microevolution the evidence for or against the operation of a superior being is simply not observable, and testing for the operation of a superior being is beyond the means of scientific inquiry. Ultimately, therefore, creationists leave scientists with no possibility but to continue to study the history of life as being controlled by materialistic mechanisms. This is not the same thing as saying that the Darwinian account of evolution is "true," but that it does continue to be the only theory that has held up to the types of investigations that lie within the domain of science."

Villee, Solomon, and Davis
Saunders College Publishing
1985, p. 1053

With regard to testable explanations of the creation events themselves I find myself in agreement with Villee, Solomon, and Davis. The most a "creation model" will ever be able to offer in terms of testable hypothesis are:

  1. the idea that all life does not share a common ancestor.
  2. the description of natural processes that would inhibit the origin of life from occurring naturally.
  3. the description of natural processes which would inhibit major evolutionary change.

For reasons of scientific discussion it is unfortunate that creationists must speak in terms of a "creation model," implying that the creation events are the subject of the model. Creationists, if they are to make any progress in science, should not contrast evolution with creation but rather with stasis, the lack of evolutionary change. Stasis is a natural phenomenon which is subject to scientific investigation.

What will we tell our students? We'll give them the data, explain the leading theories to them, expose them to the problems in our current ideas and motivate them to give us a better description of nature. We might also warn them of the "natural" tendency of scientists to assume that the history of life was simply the result of materialistic mechanisms. The truth may lie elsewhere.

Copyright © 1997 Art Battson, J. Richard Wakefield, Access Research Network. All rights reserved. International copyright secured.
File Date: 2.26.97