550 



SCIENCE. 



[N. S. Vol. XIX. No. 483. 



true that many variations of inbred domesti- 

 cated plants and animals are very abruptly 

 discontinuous, and that such changes are not 

 caused by selection,* but these facts in no vyay 

 militate against others equally obvious, that 

 the natural evolution of new types is a rela- 

 tively slov? and gradual process, and that selec- 

 tion may easily influence the direction of this 

 continuous vital motion. The older selective 

 hypothesis was only half erroneous. Selection 

 does not set stationaiy organisms in motion, 

 but it often guides spontaneous change. It 

 does not explain evolution or vital motion in 

 general, but it does explain adaptation, or 

 motion in some particular direction, as when 

 one species difl^ers from its relatives in special 

 characters which enable it to exist in a special 

 environment. That all adaptations are mere 

 coincidences is as improbable as that all char- 

 acters represent useful adaptations. 



Selection is not, as many ' Darwinians ' have 

 maintained, the true, efficient cause of evolu- 

 tion; the vital motion of species proceeds 

 whether selection is operative or not. Species 

 do not acquire characters from the environ- 

 ment, but merely in accordance with it. At 

 any point in the evolutionary journey, selec- 

 tion may determine whether certain characters 

 shall be acquired or not; it is an obstacle in 

 the environmental road over which the species 

 would travel, instead of being the source of 

 power of the organic automobile. By prevent- 

 ing motion in one direction selection may be 

 said, of course, to cause advance in another, 



cause It can not be an advantage to a plant to be 

 able to breed with only half of the members of its 

 species. The same reasoning would apply, how- 

 ever, to all the phenomena of sexual separation, 

 of which the dimorphism of bisexual plants may 

 be an incipient stage. It seems obvioug, too, that 

 to breed successfully with half of the individuals 

 of a species is an important advantage over the 

 alternative of breeding less effectively with all of 

 them. The partial or complete sterility of some 

 dimorphic plants to the pollen of others of their 

 own caste may be due to impotency rather than to 

 adaptation, and a dimorphism by which this 

 fatal result could be avoided would certainly be 

 favored by selection. 



* Except as selection implies inbreeding, by 

 which mutations are induced. 



but it is apparent that this causality is nega- 

 tive and passive, or a mere figure of speech. 

 Selection may explain why a particular char- 

 acter is accentuated in a particular species, 

 but it is no more a cause of the developmental 

 progi-ess of the species than the turns of the 

 road are the motive power of the vehicle. 

 Segregation enables species to attain difieren- 

 tial characters, and selection assists their ac- 

 commodation to environment, but both these 

 possibilities rest on the more fundamental fact 

 that organic evolution goes forward without 

 external causation in groups of diverse, inter- 

 breeding individuals. If a species stood still 

 selection could effect nothing except its par- 

 tial extinction. In the recognition of a con- 

 tinuous and universal evolutionary motion the 

 kinetic theory supplies the long-sought ex- 

 planation of selective influence. By ceasing 

 to look upon selection as a mysterious evolu- 

 tionai-y cause we are able to ascribe to it a 

 practical and easily comprehensible evolution- 

 ary function. O. F. Cook. 

 Washington, D. C, 

 March 11, 1904. 



NATURE STUDY. 



To THE Editor op Science: In the last two 

 numbers of Science have appeared articles by 

 Drs. Wheeler and Chapman on the abuses of 

 nature writing as exemplified in the writings 

 of Wm. J. Long. These articles have ex- 

 pressed the fear that such work may increase 

 and that it may invade the secondary schools 

 as supplementary reading designed to aid in 

 the instruction in zoology. That this is no 

 idle fear is brought very vividly before the 

 science teacher in the normal schools, for he 

 stands, as it were, an outpost between science 

 and its teaching to immature students. Per- 

 mit me to call your attention to a pseudo- 

 scientific extravaganza put forth in a seeming 

 serious mood which exemplifies this point. 

 Before me is a book designed evidently for 

 students of the first grades called ' The Tree 

 Dwellers.' It bears the publishei's' imprint 

 of Band, McNally and Co., 1903, and its 

 author is Katharine E. Dopp, of the Extension 

 Division of the Chicago University. The at- 

 tempt of the book is to place before the stu- 



