The Origin of New Adaptive Characters

Abstract

THE author of the article in NATURE of July 15 entitled “The Material Basis of Evolution” has misunderstood some of the chief bearings of my address entitled “Origin of Single Characters as Observed in Fossil and Living Animals”¹, and I would regret to have certain passages in this well-intentioned review quoted as expressing my opinions. My address was based on researches carried on continuously since 1889 on the actual modes of origin of single specific and generic characters as observed in several lines of mammalian descent (horses, rhinoceroses, and titanotheres) in which such characters can be traced from their beginnings to their final development without any break. The term numerical was used as a convenient designation for all characters which may be expressed in numbers and formulæ, while the term proportional was used for such characters as may be expressed in indices and ratios.² There is a clear genetic distinction between these two kinds of characters, for while changes of proportion, such as the reduction of the lateral digits of the feet of horses, gradually lead into changes which may be expressed numerically, such reduction-changes fall under laws which govern quantitative changes in general rather than laws which govern the origin of new characters.