Patterns of Specification


Review of Species Problem

Previously, 1 a sample of definitions for the term "species" was given. Presuppositions for each definition seem to be important in establishing the validity, or at least usefulness, of any particular definition. Endear 2 concludes: "It is clear that species concepts vary radically depending on their purpose, be it theoretical or operational, taxonomic or evolutionary, contemporaneous or clade, reproductive or cohesive. It is unproductive, and often positively misleading, to apply one species concept to all species, or to answer all questions."

Notice that the definitions of species as used above hinge on their explanatory power for evolutionary phenomena. If speciation were real, but subject to finite limits of variation, then microevolution very well might be confirmed without the collateral concept of macroevolution being established at all. A creationist view allows for some speciation because of the wide range of definitions, but does not support higher taxonation.

Essentialism

A variety of terms have been used in the past to describe species for the limited view of variation: immutable, 3 constancy, 4 essences, 5 fixity, 6 types, 7 and kinds. 8 The underlying idea is that organisms are grouped by limited expressions, such that gaps exist between fundamental groups. Today's young earth creationist is not a strict essentialist, in that variation is expected and thoroughly acknowledged. On the other hand, gaps between groups are said to be common, and seldom, if ever, bridged. Mayr 9 reviews the contrast of thoughts: "Essentialism with its emphasis on discontinuity, constancy, and typical values ("typology"), dominated the thinking of the western world to a degree that is still not yet fully appreciated by the historians of ideas. Darwin, one of the first thinkers to reject essentialism (at least in part), was not at all understood by the contemporary philosophers (all of whom were essentialists), and his concept of evolution through natural selection was therefore found unacceptable. Genuine change, according to essentialism, is possible only through the saltation of new essences."

Overview

Speciation, like its parent concept, evolution, is said to be a fact, even though few beginning-to-end examples can be given for it. Bush 10 states: "Furthermore, speciation is usually a rare event, seldom, if ever, observed from start to finish. Our current concepts of speciation are therefore primarily based on post hoc reconstructions of past events, or derived from theoretical population genetic models usually based on classical Mendelian genetics, with all the inherent weaknesses and speculative nature of these approaches. The post hoc approach is, at best, subjective, and it is thus not surprising that recent advances in molecular biology call into question certain widely held conclusions of the naturalists and population geneticists (Crick, 1979)."

This is not to deny that speciation occurs. Much evidence implies that isolating processes are establishing unique populations all the time. Indeed, in the case of ploidy, a new isolated species (depending on the definitions) can occur in one generation. However, if speciation (primarily reproductive isolation) is the process of microevolution, and, in turn macroevolution, as some proponents hold, then we are once again in the precarious position of declaring that the fact of speciation leads directly to the fact of macroevolution, without knowing very well how either takes place, or the causative relation between the two.

Modes of Speciation

Mayr 11 lists twelve potential modes of speciation, not all of which have been observed (reworded below by author).

Potential Modes of Speciation

Transformation of single species

1. Single species transformation by mutations, etc.
2. Single species transformation by genetic input from a second species
3. Fusion of two species by hybridization into a single species

Multiplication of species by unique events

1. Asexual species mutating into a new species
2. Macrogenesis or hopeful-monster production
3. Chromosomal aberrations leading to new species
4. Chromosomal set multiplication within a species
5. Chromosomal set combining between species

Multiplication of species by population events

1. New species formed within single populations - sympatry
2. New species formed at hybrid zones - semigeographic
3. New species formed by geographically isolated populations
4. New species formed by extinction within the range of the species.

The first three modes only involve the change of starting species totally into following species without branching. The next five modes involve speciation events that are peculiar in mechanics. The last four modes involve populations which are said to give rise gradually to more than one new species through branching. Mayr gives no detailed examples of each of these modes at this citation, but does offer some general conclusions: First, speciation has come to mean principally the multiplication of species; therefore, phyletic speciation (single species transformation) is not of particular interest to evolutionists. Fusion of species is a retrograde process for evolution, and simply may be the breeding of subspecies that were incompletely identified.

Asexual species formation is complicated by the very definition of species, which is assigned, most generally, to reproductively isolated populations. Since vegetative processes are involved, every individual is reproductively isolated from all others at the outset. Commonly, such organisms are said to belong to a collective species.

Macrogenesis is not known from real data, but is rather an hypothetical construct. Many monsters have been born, but none are known to have given rise to new species lines.

Chromosomal alterations, either in structure or number, are common. Indeed, the only direct evidence for speciation is found in the formation of polyploid organisms. Multiple sets of chromosomes make them unable to cross with the parent species; hence they become new species, even though they might look and behave very much like the parental lines.

Most speciation is said to be associated with gradual population changes under the influence of geographical differences. The mechanisms for such speciation is hotly disputed, even though the population data seem to indicate definite levels of divergence or subspecies formation. Mayr concludes, on page 513: "The widespread occurrence of geographic speciation is no longer seriously questioned by anyone."

Once again, we come to a dissettling conclusion regarding the process of speciation. Transformation within single species is not of highest importance to evolution; unique speciation events are not a major source of evolutionary change; and population events, like evolution as a whole, are said to be difficult to observe. Hard evidence (start to finish) for speciation as a major process in evolution is obviously lacking.

Mayr, on page 48 comments: "Speciation is a slow historical process and, except in the case of polyploidy, it can never be observed directly by an individual observer. . . . The method [of construction] most suitable for our purpose consists in the reconstruction of an essentially continuous series by arranging fixed stages in the correct chronological sequence. . . . Stating our aim more specifically, it should be possible, speciation being a slow process, to find natural populations in all stages of 'becoming species.'"

Summary

The wide variety of definitions for the term species today permits one to conclude that some new species are being formed from old species. Thus, speciation supporting microevolution (horizontal change), is an acknowledged phenomenon. However, the critical category of speciation that would establish macroevolution (vertical change) is said to be difficult to document as a totally observed event. Although much literature has been written to illustrate the concept, most of it is inferential. Even in these writings, a credible extrapolation of these transformations to establish higher taxonation above the species level is very suspect.

Today's creationist interpretation of speciation would be given in an essentialist perspective claiming that even though the ancient "fixity of species" dogma is disproved by speciation events, there are also practical limits to so-called "phyletic" change. These limits are seen in the historic and current documentation of discontinuities between types. This subject will be the theme of an upcoming article on "specialization."

References

[1] K. B. Cumming, "On the Changing Definition of the Term 'Species,'" Acts & Facts "Impact" No. 211 (1991); pp. i-iv.
[2] J. A. Endler, "Conceptual and Other Problems in Speciation," in D. Otle and J. A. Endler, Speciation and Its Consequences, (Sunderland, Massachusetts, Sinauer, 1989), pp. 625-648.
[3] D. Kohn, "Theories to Work By: Rejected Theories, Reproduction, and Darwin's Path to Natural Selection" in W. Coleman and C. Limoges, Studies in History of Biology (Baltimore, Maryland, The Johns Hopkins University Press, 1980), p. 69.
[4] J. Phillips, Life on the Earth (New York, Arno Press, 1980), pp. 191, 194 [Originally prepared in 1860].
[5] E. Mayr, "The Nature of the Darwinian Revolution," Science, 166 (1972): pp. 981-989.
[6] M. Denton, Evolution: A Theory in Crisis (London, England, Burnett Books, 1985), pp. 17-367 [particularly p. 19].
[7] C. Lyell, Principles of Geology (New York, D. Appleton and Co., 1853 Ninth Ed.), pp. 578-590 [particularly p. 579].
[8] H. Morris, Ed., Scientific Creationism (El Cajon, California, Master Books, 1984, Eleventh Ed.), pp. 51-54.
[9] E. Mayr, The Growth of Biological Thought (Cambridge, Massachusetts, The Belknap Press, 1982), p. 38.
[10] G. Bush, "What Do We Really Know About Speciation?" in R. Milkman, Perspectives on Evolution (Sunderland, Massachusetts, Sinauer, 1989), pp. 119-128 [particularly pp. 119, 120].
[11] E. Mayr, Animal Species and Evolution (Cambridge, Massachusetts, The Belknap Press, 1979), pp. 428, 488, 513.

* Dr. Cumming is Professor of Biology and Dean of the Institute for Creation Research Graduate School.

Cite this article: Kenneth B. Cumming, Ph.D. 1991. Patterns of Specification. Acts & Facts. 20 (5).