MACROEVOLUTION.


Partial knowledge leads to total confusion.



Macroevolution is a large-scale and long-range evolution of organisms in taxonomic categories above the species level, that is the evolution of genera, families, orders, and so on. What a strange situation is being presented by this definition! It gives the impression of realism about something that does not really exist. This is like describing a dragon as a huge, frightening, scaly beast with wings, and seven heads, all breathing smoke and fire, and somehow omitting the small detail that this beast is only a mythical monster. There is really no such thing as macroevolution. The reason for this is simple enough. The evolutionary process in its concreteness happens in terms of life and reproduction of individuals in a vast number of coexisting species, and not in the abstract world of the higher taxa. Nonetheless, we do see such book titles as Vertebrate Evolution, and Evolution of Mammals, as if evolution on the level of subphyla and classes were real. I shall examine in this presentation the validity and the fallacy of several meanings of macroevolution currently in use.
According to one common usage, macroevolution is understood as being the source of the natural taxonomic system. We assume that the system is natural because it reflects the evolutionary relationships of the various taxa including, of course, taxa above the species. This kind of thinking is begging the question. According to another idea, we discover macroevolution in the fossil record, and we find still other ideas of macroevolution implicit in studies of overlapping chromosome inversions, and in DNA, RNA, and protein phylogenies. What could be wrong with that?
I shall start here with the problem of macroevolution when we apply it to a system of natural classification. It is customary to classify all living organisms into a minimum of seven taxonomic ranks. We call these seven, obligate ranks Kingdom, Phylum, Class, Order, Family, Genus, and Species. For some people, taxonomy is a filing system. Each rank contains several subdivisions all the way down to the last file that holds the pages of the many species. All entries belong to the same system, and all ranks are just sets of files of the same logical value. There is then a great deal of confusion and arbitrariness associated with all the different taxa, including the species. I have read somewhere a rather tongue-in-cheek statement saying that a species is a species if a competent taxonomist says it is. In this kind of thinking both, the evolution of species, or microevolution, and the evolution of higher taxa, or macroevolution, are part of the same logical system. The question is being raised whether the moving forces of microevolution are sufficient to explain those of macroevolution. This last statement then closes the circle of confusion because it presents the two processes having the same, real value. Contrary to this view, it can be shown that microevolution is real, while macroevolution, if not interpreted correctly, is nothing more than speculation outside the reach of the scientific method.

There is a real difference between the biological species and all the other taxa. The difference is between the concrete and the abstract. By analogy, the difference between the species and higher taxa is comparable to that between the actual languages of German, English, and Swedish, and the abstract concept of Germanic languages. Such concept may imply the relatedness of these languages in their origin but not in their concreteness. We do not speak in Germanic but in English, German, and Swedish. Similarly, we bake an apple pie with real apples. The pie is food, it has calories, and it tastes good. We do not bake a generalized pie filled with the concept of “appleness.” Evolution is a concrete, observable phenomenon. It refers to individuals who share a common gene pool, produce viable offspring, are reproductively isolated from all others, and compete with each other for the available resources. Chordates as a phylum, Vertebrates as a subphylum, and Mammals as a class, do not feed, reproduce, or interact in any way. None of the facts of life apply to the higher taxa. The only existing evolutionary process is microevolution on the level of the species.

The conceptual contradiction implied by the term, macroevolution, becomes even more clear when we consider the way the evolutionary process was first discovered. It is through the scientific method that we know about biological evolution. The primary discoverer of the evolutionary process was Charles Darwin who somehow instinctively made good use of this method at a time when it was not yet clearly formulated. During his five years long voyage around the world on the ship H.M.S. Beagle in the early 1830s, he observed and described a multitude of data about living things. These years represented the first stage of the scientific method. An entry in his Autobiography indicates that he formulated his hypothesis on evolution of species by means of natural selection in 1838. The eleven years after that, until the publication of The Origin of Species in 1859, represented the time of systematic inquiry, or the “experimental” phase, of the study. During these years, Darwin gathered an enormous volume of evidence both for and against his hypothesis. In spite of many difficulties, the evidence he obtained supported his original ideas.

What did Darwin propose in the Origin? His first statement was a reflection on the variation of all living things. Next, Darwin stated that we should study and understand this natural variation in the concreteness of the way of life of organisms as they live in their actual environment. He also found that the relationship between the variants, their many offspring, and their environment of limited resources, results in competitive stress. Under such conditions only the most successful variants survive and leave offspring transmitting the successful traits from generation to generation. Darwin named this process of elimination of the unfit and preservation of the fit, natural selection. Since the environment is not static but is constantly changing, the concrete meaning of fitness must follow these changes, continuously altering the forms of living things. Darwin also recognized that the basic biological units of such evolutionary changes are the species.

These statements in the Origin were the results of careful and extensive observations and inductive reasoning. Every one of these fundamental tenets of biological evolution has been well established, and can be studied experimentally by measuring, comparing, and evaluating them. There is no logical gap between the premises and the conclusion of Darwin’s thesis. The evidence that the biological species is a process phenomenon is overwhelming. Studies of natural populations reveal the polytypic and dynamic characters of the species creating the need for such process terms as subspecies and semispecies.

There have been, since Darwin, but few conceptual changes added to this overall picture of evolution. For one, we know today about the sources of variation of which Darwin was not aware. We also know that survival is not a matter of a yes or no situation but is a matter of degrees. It is, therefore, more appropriate to speak of the differential survival of variants then just of the survival of the fittest. We also know that, besides the controlled changes produced by natural selection, there are also random factors that contribute to the evolutionary process. This is the picture we gather on evolution through the scientific method, and we call it microevolution.

This process is real, it takes place right here and now in our time, but it happens on the level of the species. Here we do not speak about the evolution of vertebrates, or mammals, or primates, but about changes that occur in the composition of species and lead to their differentiation. We should also keep in mind that in the terms of microevolution we do not use the word “origin” in an ontological but in a phenomenological sense. What the scientific method captures for us is a short sequence of events about the biological realities of populations whose nature is to be varied and to be able to change.

How can then we speak about evolution in the often strange, prehistoric forms of life? Some would immediately say, well from the fossil record of course. The fossil record is valuable because it tells us about certain features of once living organisms of which we would have absolutely no knowledge otherwise. The fossils are a true record of ancient forms of once living organisms but, because of the nature of fossilization, this record is fragmented and incomplete, and it is very much biased, because the conditions of fossilization are biased. We may speak about evolution today as we observe this phenomenon, and we may speak about evolution in the past as we study the fossil record, but there is a fundamental difference between these two approaches. One is about the concrete, the other about the speculative. Our evolutionary ideas about the fossil record are not based upon direct observation but on the reasonable assumption that the processes we observe today as effective, were also present and effective in the past. In other words, we do not prove evolution from the fossil record but we interpret this record in evolutionary terms based upon reasonable assumptions. Of course, assumptions, even very reasonable ones, lead us into a world of arbitrariness and speculation. This becomes obvious when we attempt to tackle such difficult topics as the origin of life, and the nature of the primitive earth. The use of assumptions is legitimate in those situations only where no direct information is available. In that case, however, we should never make the error of assuming that our reasonable assumption is of the same value as the conclusion of a scientific inquiry using the scientific method.

What is a reasonable assumption? Are there any valid criteria to guide us? Instead of making a philosophical argument about the nature of reasonable assumptions, I propose a more concrete and practical approach. Can the data of microevolution explain satisfactorily, given enough time, the evolution of traits of higher taxa? Take, for example, the evolution of mammals. What we are really considering here is not the evolution of a taxon, that is, the evolution of the class of mammals, but that of traits that we use today to classify living organisms into the class of Mammals. Considering the mammals as we know them from the fossil record through the Cenozoic era, we find a progressive appearance of traits that we use today to classify mammals into orders, suborders, families, subfamilies, genera and species. We find that the species characters of today appeared in the Pleistocene and Recent epochs of the Quaternary, and the higher we go on the taxonomic scale the older are the characteristic traits. For instance, we find that many archaic mammalian traits appeared in the Paleocene of the Tertiary period, while the traits that characterize the modern orders, families, subfamilies, and genera, appeared in the Eocene, Oligocene, Miocene and Pliocene respectively, and in that order. I would say, that an assumption that explains this phenomenon of the fossil record in evolutionary terms is reasonable if it is based on what we know about the evolutionary process through the scientific method. Since it is microevolution that is revealed by this method, it seems to me, it is reasonable to assume that the various traits used in the classification of higher taxa were species traits in the past when they were first formed by the evolutionary process.
Of course, this does not mean that the traits we use today to classify living things into higher taxonomic ranks are not influenced by natural selection any more. There is, however, an important difference between the evolutionary significance of, let us say, class traits and species traits. The former are far more buffered against changes than the latter. This difference is due simply to distribution. To illustrate the point, consider the evolutionary event of extinction. A species becomes endangered when the numbers in it are brought below a critical value, an event that may come about relatively easily. In contrast, to render the mammalian class extinct would require to render all the species extinct that we classify into the numerous genera, families and orders of this class. Such an event is far less likely to occur than the extinction of a single species. In any case, all evolutionary events today are played out in the realities of living individuals of existing species. These are micro-evolutionary changes. These we observe directly in our own time, and they are the basis for reasonable assumptions about the past.

We reach the same conclusions when we consider other forms of macroevolution such as chromosome inversion, DNA, RNA, and protein phylogenies. In all these studies we should be keenly aware of the differences between the concrete and the speculative, that is between the actually observed and the reasonably assumed. We should be always honest and cautious. When we indulge in a flight of fancy and speak about such things as the origin of life, or the nature of the primitive earth, we should never look upon our assumptions as if they were proven facts, even if they have a tremendous appeal. Our arguments may be impeccably logical, nonetheless, we should be weary of them if we base them on assumptions. Being logical and being certain are two very different things.


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