EVOLUTION NOT THE ORIGIN OF SPECIES. 451 



and with any or all its characters changed.* It is not necessary even 

 that the individuals of a species remain alike; in many unrelated 

 natural groups extremely diverse sexes, castes and ' forms ' remain asso- 

 •ciated in the same species and travel together on the evolutionary 

 journey, sharing the same environment, but without any tendency to 

 become 'exactly alike.' Moreover, we know that sexual and other 

 diversities inside the species are not casual or accidental, but normal 

 and advantageous, facts quite overlooked in static theories, which have 

 viewed life from a narrowly systematic standpoint and have argued 

 that interbreeding prevents the preservation of new characters and is 

 thus a hindrance to evolution. 



The kinetic theory, on the contrary, ascribes the fact that organisms 

 are everywhere bound up into species to a property of fundamental 

 evolutionary importance, and interprets the multitudinous devices for 

 maintaining the coherence of groups of interbreeding organic indi- 

 viduals and the equally general manifestations of sexual and other 

 diversification inside specific lines, as due to the same requirement of 

 protoplasmic organization, an interlacing network of descent. With- 

 out cross-fertilization species would not cohere, but would split into 

 numberless independent, diverging lines. This takes place with organ- 

 isms long propagated asexually, whether artificially or in nature. For 

 example, the genus Sphagnum, which very rarely produces spores, offers 

 a multiplicity of varieties nowhere approached among mosses having 

 normal sexual reproduction; but notwithstanding so many differences 

 in minute details Sphagnum has remained a very compact, unpro- 

 gressive group. Cross-fertilization prevents this type of diversification, 

 but it need not on that account be supposed to impede evolutionary 

 progress. Evolution is not merely a progressive diversification, it re- 

 quires also a progressive synthesis of characters by the interbreeding of 

 the individual members of specific groups. 



The Species a Protoplasmic Network. 

 That sexual reproduction is a substitute or improvement of multi- 

 plication by fission is another partial and misleading view which has 

 contributed much towards the concealment of the causes of evolution. 

 The division of cells is the only method of organic increase; conjuga- 

 tion is not multiplication, but serves as a preliminary stimulant to the 

 necessary cell-division. What is growth, for example, among the 

 filamentous algge composed of chains of cells is reproduction among 

 the unicellular species, where divided cells become separate individuals. 



* ' Four Categories of Species,' American 'Naturalist, 33:287, April, 1899. 

 The ' species ' into which paleontologists arbitrarily divide geological series of 

 organisms may be explainable by evolutionary progress alone, but the multi- 

 plication of the contemporaneous species of a given horizon is a different 

 question. 



