The Logical and Empirical Bases
of the Theory of Evolution


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The language of science, in discussing the theory of evolution as it pertains to the origin of species, speaks in terms of animals that “must have existed” to fill the gaps in the paleontological record of evolution and in terms of chemical reactions that “would have taken place” in order to generate the first organic material that “had to have lived” in the primordial seas of the young earth. This is the language of pre-theoretical hypothesis, which suggests that the “theory” of evolution is in a tenuous position as regards its logical and empirical foundations. Because much of the biological history that is projected into the past is drawn from the logical implications of principles observed in the laboratory, it is vital that bio-science recognize that which is, and is not, demonstrable under controlled conditions of genetic mutation, selection, isolation and speciation. Otherwise, science is speculating and hypothesizing about phenomena which are largely unverifiable on an empirical basis, due to the unmanageably large time element involved in practical demonstrations. The object of this paper is to establish the logical and empirical bases of contemporary knowledge of speciation in the light of contemporary criticism of the theory of evolution.

Reproducible experience is the basis of explanation or proof of scientific theory, and the scientist most effectively explains unfamiliar phenomena in terms that most closely approximate experience. One such experience is the birth or division of living organisms from precedent organisms that may go back few or many generations within the span of scientific observation. Because the independent disciplines of astrophysics, geology, and paleontology have indicated that the earth, living organisms, and man have not always pre-existed, the question arises: at what point the process of organic reproduction began? A very ancient and powerful tradition maintains that plants and animals were created instantaneously and reproduced themselves thereafter. However, creation is not a reproducible experience for the scientist and is rejected as an explanation in favor of phenomena which are more familiar, in this case, the infinite extension backwards in time of the reproduction process.

Since the paleontological record has demonstrated that progressively more sophisticated forms of life have appeared progressively in time, the logical implication of the backward extension of the reproduction process in time is that all organisms are descended from more primitive organisms or chemical processes. The question then arises of the mechanism by which the transformation of species, one into another, takes place, for it is transformation and not creation that accounts for the appearance of new objects and entities within human experience.

At this point, it must be acknowledged that nothing of human or organic evolution has been “proven” in the popular sense of the term, we have only adopted the best theory in terms of minimizing the gap between imagination and experience in accounting for the existence of life on earth. What, then, has the scientist observed or experienced to explain the “origin” (i.e., transformation) of species within the historic framework established above? An appropriate starting point is the hypothetical first, presumably single-celled, organism. In 1922, a Russian biochemist, A. I. Oparin, proposed the theory that organic compounds had a long history of biochemical evolution before living forms appeared. H. C. Urey later described the primordial earth’s atmosphere in terms of its chemical and thermal qualities, and, in 1953, S. L. Miller performed an experiment reproducing these conditions in the laboratory. This and later experiments produced at least 15 amino acids as of 1968, as well as nucleotides and the bases adenine, guanine, uracil, cytosine and hypoxathine. Experiments reproducing more specialized volcanic activity have formed copolymeric “protenoids” which may be regarded as pseudocells (Williams, 1973: 93–97). Life has not been reproduced, but much has been demonstrated in this direction.

Given the existence of an ancient alga-like body 3.5 billion years old (for lack of fossilized single cells), science must now account for the production of more advanced organisms in view of the seemingly fundamental immutability of species. First of all, nature and the laboratory have demonstrated that organisms are not immutable and that species are not hard-and-fast categories of organisms. Conspicuous and identical mutations have been produced in the evening primrose (Oenothera) and the Drosophila fly to such a degree as to create a dispute in the scientific community over the utility of gross versus micro-mutations in the speciation process (Stebbins, 1963: 24). Further, the definition of a species as all intra-fertile members of a population group is blurred by the fact that fertility in and among population groups is differential and not absolute. In some cases (e.g., the siabon), the production of offspring cannot even be anticipated, which gives the definition of species an ex post facto, operational character. Finally, the synthetic theory of evolution postulates that the demonstrable plasticity of organisms manifest in genetic recombination, assisted by mutation, is the vehicle of change in the inward and outward characteristics of living entities (Stebbins, 1963: 26–30).

If evolution proceeds in the relatively slow and incremental fashion implied by the progressive recombination of genes, why do new forms emerge? The contributions of geological history and a certain degree of Malthusian economic logic are vital in answer to this question. The meteorological and geographical changes of environment in earth’s history have corresponded with the appearance and extinction of many animal species, which suggests that environment exerts a natural selective pressure on organisms to effect the survival of the relatively fit among organisms in competition for resources which will not sustain all the competitors. Thus, “Natural Selection” and “Survival of the Fittest” are prominent and indispensable concepts in synthetic evolution theory.

Critics have suggested that the notions of natural selection and survival of the fittest are a matter of divine ordinance in the former case and of meaningless tautology in the latter. It is claimed that the appearance or disappearance of species is foreordained according to a “plan” or design, but, in the absence of a demonstrable pattern in support of this claim, the scientist must retain his belief in natural causes for the fertility and mortality of organisms, which not only compete, but maintain an equilibrium, in relation to scarce resources. Fitness is criticized as being meaningless because the evolutionist supposedly pronounces an organism “fit” after the fact of its survival, rather than being able to predict the future success of an organism. Because larger size, greater strength, or greater speed do not always contribute to survival, it is maintained that “fitness” merely refers to those qualities that contribute to success, without specifying “a priori” what those qualities are. Admittedly, a general formula for fitness in organisms would be impossible of achievement, but specific relationships between organisms and environments can be analyzed for the relative efficacy of certain characteristics (e.g., the English peppered moth) (Stein and Rowe, 1974: 119).

With the emergence of new forms of life arises the problem of preventing their submergence in clinally related gene pools, which would preclude the possibility of speciation. The science of plate tectonics has provided a virtually indisputable argument for the possibility of absolute isolation of sub-populations of a species from one another. Further, the anatomical and physiological similarities between continentally isolated species lends support to the probability of their common ancestry and subsequent speciation through isolation (e.g., old world and new world monkeys). However, disputed probabilities are not proof of speciation, and the scientist must turn to the laboratory for a demonstration of otherwise unobservable phenomena. Contrary to popular belief, speciation has been demonstrated under laboratory conditions with the artificial creation of doubled hybrids called “amphiploids,” which are reproductively isolated by hybrid inviability or sterility from pre-existing populations. Unfortunately, the natural production of differing species may still be disputed, because amphiploids are rare or lacking in the animal kingdom (Stebbins, 1963: 35).

At this point, the central themes of genesis, mutation, selection, isolation and speciation have been examined for their logical and empirical foundation, but there remain some fringe issues that illustrate the futility of argument over biological history without reference to scientifically observable and reproducible phenomena. The horse series of fossils from “eohippus” to the modern horse is sometimes adduced as evidence of anagenetic speciation, but the operative character of the definition of species makes it impossible to do other than make a judgment of the degree, if any, of speciation involved. Another dispute concerns the implication of human possession of “vestigial” organs such as the appendix, caecum, coccyx, and ear muscles and of the “itphylogenetic” ontogeny of the human embryo (Riegle, 1971: 67–69). Again, a demonstration of more primitive ancestry is impossible; one can only point out the improbability of alternate hypotheses.

A final issue is that of the supposed absence of transitional forms in the fossil record of evolution, though many of the gaps in the record can be explained in terms of fossil biasing factors. In any case, none of the last-mentioned issues can ever be resolved except by implication of the demonstration of central phenomena (genesis, mutation, selection, isolation and speciation).

References and Selected Bibliography

  • Alland, Alexander, Jr. Evolution and Human Behavior. New York, Anchor Press/Doubleday
  • Korn, Noel and Smith, H. R. (eds). Human Evolution. New York, Henry Holt and Co., (1959)
  • Kurtin., Bjoern. Not From the Apes. New York, Pantheon Books, (1972)
  • Poirier, Frank E. Fossil Man: An Evolutionary Journey. St. Louis, C. V. Mosby Co., (1973)
  • Rensch, Bernhard. Homo Sapiens: From Man to Demigod. New York, Columbia University Press, (1972)
  • Riegle, David P. Creation or Evolution? Grand Rapids, Zondervan Publishing House
  • Stebbins, Ledyard G. Dynamics of Evolutionary Change in Lectures in Biological Science, Townsend, J. I. (ed). Knoxville, The University of Tennessee Press
  • Stein, P. L. and Rowe, B. M. Physical Anthropology. New York, McGraw-Hill
  • Wendt, Herbert. From Ape to Adam. New York, Bobbs Merrill Co., (1972)
  • Williams, B. J., Evolution and Human Origins. New York, Harper & Row