The Status of the Species and the Genus

Abstract

I. STRUCTURES AND ORIGIN THERE seems to be no valid based on a single character. So-called physiological species, differentiated by a single physiological character, are typical varieties, not subspecies, which are geographical units (see below). Any one species in a genus is differentiated from every other species by a set of morphological, as well also as physiological and habitudinal characters. Therefore a species originates, not by a change of one character, but by several contemporaneous changes. Such combination changes are claimed to originate in three ways: 1. By Hybridizatiom. This may occur where species overlap or where an individual is suddenly dropped into a new locality. If this field is fruitful, novelties should be sought for chiefly where congeneric species overlap. 2. By Environmaertal Stimulus. That there is such a thiig has been amply proved by the North American Fauna series of the U. S. Biological Survey where one finds that desert regions consistently imprint certain characters on its mammals (also true of birds, snakes, insects and others), that humid areas consistently imiiprint their characters, dune areas theirs, etc., so that definite subspecies are found in each of these habitats with certain characters modified in the same way. These subspecific (geographical) characters have since been found to be constant on transplantation. Further, these changes check with industrial m-nelanism in Lepidoptera (1), which phenomenon ought to be checked in the Pittsburgh region. Finally alpine dwarfing retains its characteristic in sea-level gardens. Such environmental changes are known as mass changes, because they affect all the individuals of a popu-