General Discussion

Abstract

The first consideration which arises in any discussion of symbiosis is the connotation to be attached to the term. In what sense, if any, can the symbiotic organisms be regarded as constituting a unity? The ‘struggle for existence’ presupposes antagonism between organisms whether or no they belong to the same or diverse a species. On the other hand, the question remains whether associated species tend to provide for each other a favourable environment. The analysis of the relations between organisms has been dominated by the notion of ‘competition’ or ‘struggle’ and the converse notion of ‘co-operation’ has in consequence been disregarded. It should be remembered that even with regard to the unitary organism the notion of ‘struggle’ between organs has been seriously advocated. The data of ecology serve as a challenge to this view of the predominant role of ‘struggle’. It will be generally accepted that the individual organism represents a true unity, and the persistence of the species bears witness to this fact. In this case the unity of the organism and the transmission of this unity from generation to generation is achieved by a genetic mechanism; nevertheless, the uniformity of genetic constitution throughout the cells of a single individual permits of differentiation of the cells into tissues and organs with diverse physiological functions displaying a ‘division of labour’ between the various organs. The unity of the organism expressed and recognized in the persistence of form within the species thus embraces a diversity of functioning within the constituent parts; and thus the unity may be regarded as a ‘functional unity’ or ‘functional field’. Each organ by its activity provides factors essential for the activity of other organs. The recent advances in the study of hormones as regulating factors in development and coordination is only one aspect of this functional unity.