Peoblems and Concepts of Evolution 3 



NATURE OF THE INDIVIDUAL. 



At present the most important question confronting us, aside from the 

 determination of what life is, is probably the question as to the nature of the 

 individual, which is in nature the unit of action in the attaiument of the evolu- 

 tion and distribution of living species. 



Two concepts seem to dominate the present situation : ( 1 ) That the individual 

 is a mosaic, composed of lesser entities, unit-characters, biophores, or similarly 

 conceived ultimate vital units, each the carrier of some one or more characters 

 of the organism; (2) that the individual is an indivisible entity, or the unit of 

 existence. Between these views there has been ia the past no compromise; 

 either one or the other, in the opinion of the adherents of the special concept, 

 must be true, and in the last decade the data derived from the neo-Mendelian 

 investigations has, in the opinion of many, strengthened the mosaic conception. 



If the factors and determiners discovered iu these Mendelian investigations 

 are thought of as carriers in the Weismannian sense, the evidence obtained by 

 the workers with this principle can be construed to support this mosaic concep- 

 tion. The ideas of the nature of these gametic agents are, however, changing, 

 and the most active and progressive neo-Mendelians no longer regard them as 

 ultimate imits, the carriers of characters, but as agents whose presence or 

 absence within or without the organic system is productive of specific end- 

 results or directions of reaction in the general operations of the mass. In this 

 sense the individual and the line of descent must be conceived of in terms of 

 associated gametic and environic factors of composition that must be present 

 and in specific relations for the purpose of maintaining the integrity of the 

 individual in its characters and in descent. In other words, the individual is a 

 compound of physical agents — ^factors, determiners, inhibitors, accelerators, 

 and so on — ^not one of which is anything more than some non-liviug mass or 

 some physical relation within or without the mass, which by its presence decides 

 the course and extent of some one or more residting reactions and the products 

 thereof ia the development of the individual. 



In non-living materials there is present in all substances and reactions these 

 agents or factors of operation that are productive of the end-result or the specific 

 compound or substance. Zinc, sulphur, and oxygen are quite unlike when 

 isolated, and all are different from water ; nevertheless, when combined under 

 the proper conditions of the medium to permit of certain reactions between 

 them, there results crystalline zinc sulphate, a substance with specific qualities, 

 attributes, and conditions of being, no one of which was brought ia by any of 

 the components, but which are the products of the reaction of the component 

 constituting agents of the specific mass. The mass is a unit, an individualized 

 entity, whose integrity and totality of characters and capacity of reaction is 

 entirely dependent upon the Tetention in this mass of the position, proportions, 

 and relations of the agents that entered into its production in the first instance, 

 and change in any of these results is a change in the composition of the mass, 

 its characteristics, and ia its reaction capacity. 



In organisms there is no a priori reason why exactly the same conception is 

 not true, both with regard to constitution and also with respect to its capacities 

 for changed reaction. The results of the neo-Mendelian investigations have 

 shown an abundance of instances in which the demonstrated presence or absence 



