THE CAUSES OF EVOLUTION

Abstract

The writer begins by reaffirming the evolution concept and the uncertainty of Darwinian theory. He proposes to discuss only causes of evolution but gives a brief summary of evidences. That changes result from environmental conditions is admitted; but "changes producible in .... a few generations have been of .... subordinate importance in evolution." Five causes of deeper transformations are listed, viz., random heritable variations, heritable variations due to action of the environment, internal and not random causes (Berg's nomogenesis), variation due to hybridization, and selection. Among more recent contributions he discusses neoteny and caenogenesis, emphasizing Bolk's theory of foetalization in man, and mutation. He proposes to answer the following questions: What is the nature of heritable differences within species? Are differences between species of the same character? Does selection occur in nature? Does it account for the formation of species? Must we allow other causes? Is evolution good or bad, directed or undirected? In answer variation within species is treated with a discussion of the principles of genetics, and mutation "enables us to escape from the impasse of the pure line." Interspecific and intraspecific differences are of the same nature. Natural selection is considered mathematically. The rate is in direct relation with the number of recessives in the population. Combinations of genes may have unsuspected effects on selection values. Hybridization is a source of rapid jumps by allopolyploidy. Selection may be overcome by mutation only when the mutation concerned has very slight selective disadvantage. The superficiality of observed characters and the probable existence of subtle adaptive values for which we have no measure are emphasized; probably competition based on embryonic growth rates and gametic characters was important in past evolution. A strong anti-Lamarckian opinion is expressed and natural selection is regarded as the main cause of evolution, based upon changes of unknown origin for which we must study variation and its causes. In conclusion vitalistic philosophies are unfavorably received and our essential ignorance of values and possibilities in evolution is frankly acknowledged. The author holds an optimistic opinion that mind and possibly unknown emergents may play an important part in future evolution. An appendix contains an outline of the mathematical theory of natural selection. || ABSTRACT AUTHORS: A. W. Lindsey