Science in Christian Perspective

The Species As A Field For
Gene Recombinations
DONALD S. ROBERTSON

From: JASA 11 (June 1959): 2

The Bible tells us that Adam was the first systematist, for after the creation of living things, God gave him the job of naming them. Ever since then, man has been busily at this task, which is far from complete, as anyone who is familiar with the field of biological classification is well aware. If Adam was successful at all in naming living things, he must have used some system of classification to distinguish one kind from another. What system he used, we do not know, for there are many different criteria that can be used to distinguish between living organisms. For example, they can be classified as to color, habitat they occupy, size, mode of locomotion or structure, etc. What groups a classifier will recognize depends upon the system of classification being utilized. For example, if mode of locomotion is used, the bird and the bat may be includ ed as a single kind, while they would be in separate groups if structure is the criterion chosen. This needs to be kept in mind in any discussion of the Bible kinds. It may be that the Bible does not use the same criter ion for distinguishing kinds that modern science does. 

Now when the scientist came along, he really took God's command to name living things seriously and set about establishing a system of classification that would adequately house all life. This system, depend started with Linnaeus in the 18th century. Linnaeus used the species as the basic unit or kind of this system. Originally the species was defined in purely mor phological terms, which is still the primary criterion used for recognizing species today, as anyone who has ever used a key to classify plants and animals knows. This system of classification, depending on form, was thoroughly worked out before the formula tion of our modern ideas as to what is responsible for the form. Today it is recognized that what an organism looks like, its morphology, or to put it in genetic terms, genetic basis its phenotype, depends to a great extent, on its genotype (another genetic term that stands for the genic make-up of the individual). In the light of modern genetics, the morphological similarity that distinguishes the members of a species results from similar (although not necessarily identical) genotypes.

Sexual reproduction provides an individual with its genotype from out of the pool of genes that the mem ber of a species have in common. Since all members of a species are sharing the same genetic resources (gene pool), and since the genes determining morphology, there will result a certain fundamental similarity between members of a species^1.  This does not mean that each member of a species is identical to every other, for in the gene pool there will be many different  forms of many genes (alleles), which can be combined in different ways to produce the individual variations found in any species. It follows then that different species are different because they have different pools of genes to choose from. These pools are separate and distinct, and will remain so as long as sexual repro duction does not take place between them. If it did to any great extent, a new and larger gene pool would result which would combine the characteristics of each of the original ones. Reproductive isolation then be comes an important criterion for distinguishing two species under the gene pool concept.

Thus a species is a group of organisms between which there is a more or less free exchange of genes and which is isolated from any similar group by a re productive barrier.

Modern biologists do not view species as static things, but as Dobzhansky puts it, they are ". . but a stage in the process of evolutionary divergence. Species are formed when a once actually or potentially inter breeding array of Mendelian populations becomes seg regated in two, or more reproductively isolated arrays. Species are accordingly, groups of populations, the gene exchange between which is limited or prevented  in nature by one or by a com bination of pro ductive isolating mechanisms"(2). The fact that species are not static but are dynamic systems is the primary reason for the so called "species problem" that we are considering in this symposium.

The gene pool concept of a species may be theoreti cally correct, but in reality it has done very little to change the work of the systematist in classifying forms. He still depends primarily upon morphological char acters without any, or very little knowledge of their genetic basis.

REFERENCES

  1. In reality we have over simplified the role of the genotype in determining morphology. The ultimate phenotype of an  organism depends upon an interaction of its genotype with the environment in which it finds itself. The same genotype might result in very different phenotypes if environmental conditions are diverse enough. However, basically it is still the genotype which determines how the expression of phenotype will be influenced by environment and to what extent.
2 . Dobzhanskv, Theodosius. Genetics and The Origin of Species, 3rd Edition,  195 1. p. 262. New York: Columbia University Press.