454 Morpho genetic Factors 



comparable to those upon which natural selection is effective. One cannot 

 discount the possibility, of course, that in the very beginning this regula- 

 tory normativeness may have arisen by a selective process and later be- 

 came established as a general characteristic of all life. 



An essential aspect of organization and of the organic forms that result 

 from it is that these involve much more than a series of successive chemi- 

 cal steps, for form is concerned with relationships. In an earlier chapter 

 evidence has been presented that relationships, and thus form, are 

 genetically determined, but how genes act to produce this trait is far 

 from clear. An organized system is a complex pattern of such relation- 

 ships and one that is not static but changes during development and 

 restores itself if altered. Whatever its origin, the problem still remains as 

 to how, in terms of protoplasmic activity, such a self-regulating, pat- 

 terned system is produced. 



One of the simplest explanations is that proposed by Child ( 1941 ) and 

 others who point out that an organized system does not develop unless 

 a polar axis is first established in originally homogeneous material by the 

 influence of an environment that differs on the two sides and that a 

 gradient arises along this axis. The essential importance, at least at the 

 beginning of development, of an asymmetric environment must not be 

 forgotten, an environment which, so to speak, "lines up" the undif- 

 ferentiated egg or mass of tissue in one direction and so orients it that 

 it can then organize its developmental pattern in an orderly fashion. Grav- 

 ity and unilateral light are the commonest asymmetric environmental 

 factors for plants. They make one side of the structure different from 

 the other and thus begin the continuing process of differentiation. Plants 

 grown where these factors are uniform on all sides are usually amorphous 

 (p. 137). The interaction between the polar gradient and the genes of the 

 organism is an important factor in producing a specific form. For some 

 biologists this explanation is sufficient to account for organic form, but 

 it does not give a clear picture of how such interaction works nor does it 

 explain the complex correlations that occur during development. 



Among other suggested explanations one of the most promising is the 

 concept of a biological "field" in conformity to which development takes 

 place. Gurwitsch ( 1923 ) assumes such a field to be present around a 

 developing organic structure, but this is difficult to describe in physical 

 terms. In Gurwitsch's hands it acquires an almost mystical character and 

 seems to resemble nothing so much as an astral body immanent in and 

 around the growing organism. Where such a beautifully precise structure 

 as a fungus fruiting body molds itself out of a complex and intertwining 

 tangle of sliding hyphae, or where from a throng of individual myx- 

 amoebae a specifically fashioned sorocarp develops through their inter- 

 action, we must assume that in the mass of living stuff there is a formative 



