Major Patterns of Variation j 277 



tinction. The discontinuities in the taxonomic description of variation 

 patterns reflect extinction pkis generous samphng errors. Examina- 

 tion of the fossil record has resulted in a classification of the major 

 patterns of phylogenetic change as splitting of lineages, phyletic 

 evolution, and quantum evolution. Rates of evolution appear to have 

 fluctuated widely in the course of time. In addition to the standard 

 rates for a group, there often have been unusually slow and unusu- 

 ally rapid rates. The so-called problem of the origin of higher tax- 

 onomic categories is seen to be a composite of linguistic, analytic, 

 and evolutionary problems. 



REFERENCES 



Rensch, B. 1960. Evolution Above the Species Level. Columbia Univ. 

 Press, New York. An interesting analysis of evolutionary patterns, pri- 

 marily in animals, with detailed consideration of trends in evolution 

 and of the evolution of the nervous system. 



Simpson, G. G. 1953. The Major Features of Evolution. Columbia Univ. 

 Press, New York. The most thorough and general account for zoology 

 of the patterns of phyletic change and their explanation in modern 

 biological terms. Simpson's more recent chapter in Sol Tax [ed.l. 

 Evolution After Darwin, Univ. Chicago Press, Chicago, 1960, vol. 1, 

 pp. 117-180, is an excellent brief consideration of the problems. 



Stebbins, G. L. 1950. Variation and Evolution in Plants. Columbia Univ. 

 Press, New York. The best source for an overall view with genetical 

 orientation of the record of past plant life. The chapter The evolution 

 of flowering plants, by D. I. Axelrod in Evolution After Darwin, op. 

 cit., pp. 227-305, contains more recent work on the Angiospermae. 



