Teaching the Major Concepts: Evolution

Abstract

I would like to speak of four aspects of the study of evolution which seem to me to be particularly fruitful approaches for the teachers to hold the interest and illuminate the understanding of the students. First, historically, it was the concept of evolution w hich made possible some unity, some cohesive theory, in the enormously complex array of data and hypotheses which is biology. Second, the history of the world of life and its diversification from relatively simple beginnings is evolution, as studied in the paleontological record. Thus viewed, evolution is the Creative Act itself, than which there is nothing more fascinating. Third, because the data of evolution are drawn from all fields of biology, almost every lesson and experiment can be used to illuminate the subject of evolution in one way or another, or conversely, evolution supplies the rationale for every lesson. Finally, our knowledge of evolution is a fascinating mixture of well established facts and laws, reasonable secure hypotheses, tentative hypotheses, and tantalizing areas of ignorance. For this reason, it is a subject ideally suited for demonstrating to students the important facts that the books are not the final authorities, and that there are new frontiers of knowledge to challange them. Let us discuss each of these points briefly. I have stated that the concept of evolution made possible some cohesive theory in biology. That biology participated in the great upsurge of the sciences in post-Renaissance times is well-known. The names of men such as Spallanzani, Redi, John Ray, Wolff, and Buffon are known to all of you. These nmen accumulated an enormous store of biological data, a store, however, which was rather chaotic, for there simply was no theoretical framework within which this vast array of data could be ordered. Linnaeus partially filled this gap with his systematic studies, in which he tried to classify the entire world of life, indeed, the entire phenomenal world. The net result, however, was that he stimulated further biological exploration and fact finding without really satisfying the need for a fundamental theory, for the taxonomic system itself was not explicable. This may be illustrated by the problem of the construction of diagrams to represent the facts of taxonomy. Linnaeus at first tried diagramming these data as a map, with each species being assigned a certain area, and those species which resembled each other most being assigned adjacent areas. But however many times such a map might be redrawn, two defects seemed to be unavoidable: some similar species had to be separated, and some dissimilar species had to be placed side by side. It was finally concluded that a map simply was not a workable model of the organization of the living world. Many other models were tried, but all failed until the idea of a tree of life was tested. Diagrams based upon this concept worked, yet no one could understand why this should have been so, so long as the concept of evolution was not a part of the biologists' intellectual equipment. Thus, by the time the Origin of Species was published, there was in the biological literature the accumulated data of 200 years of intensive biological exploration and experimentation, a burgeoning chaos. The concept of evolution provided the theoretical framework into which these previously disorganized facts could be arranged in meaningful order. Thus it became obvious that the data of taxonomy could be diagrammed as a tree, 'Presented to the Joint Symposium of the Teaching Societies at the AAAS meetings in Indianapolis December 28, 1957.