262 ESSENTIALS OF BIOLOGY 



functioning or structure confers advantage upon an organism 

 so that it will tend to live longer and reproduce more often than 

 do organisms of the same race that have not made the adaptation. 

 And conversely a mutilation must expose the organism to some 

 disability so that it will not live so long, nor reproduce so often 

 as do those that are not so mutilated. But all this need not lead to 

 transformism. In order that this may occur it would be necessary 

 that the adaptation, say, should not only be something that is novel 

 but that it should also be such a change that will necessarily occur 

 in the progeny of the organisms in which it first appears. Now 

 leaving, for the moment, this question of the inheritability of 

 acquirements we may conveniently discuss the logical argument 

 for Lamarckian transformism. 



Urges, needs and desires in organic behaviour. We have seen 

 (Sections 46 and 47) that the animal so behaves as to maintain 

 itself in a condition of normality. It so acts as to maintain its 

 own individual existence and to reproduce. If the environmental 

 conditions change, it so modifies its behaviour as to establish 

 new relations with regard to the things outside itself such that 

 the state of normality may be restored. It has still its urges to 

 live and reproduce and these must be satisfied if it is to retain 

 its normality. Its urge to grow and reproduce is indefinitely 

 great and is limited only by the opportunities that wild nature 

 affords for nutrition, shelter, and space for the indefinite distribu- 

 tion of its progeny. Therefore by " normality " we must also 

 understand the potential increase of its race to an indefinite extent. 

 So even should the environment remain the same the organism 

 and its progeny must continually endeavour to find in it new 

 opportunities for nutrition, defence against enemies or unfavour- 

 able conditions, and for reproduction. 



If these urges are not satisfied the organism must experience 

 needs and desires. It does not follow that such needs are '' felt " : 

 they may be experienced unconsciously as lack of normality. 

 There is simply dissatisfaction, whether the lack is consciously 

 experienced, as it doubtless is so experienced in ourselves and 

 many other animals, or whether it unconsciously affects behaviour. 

 We experience dissatisfaction, or lack of normality, when we are 

 hungry, but even when we cannot attribute the unconscious feeling 

 of hunger to an organism there must, nevertheless, be an urge to 

 renewed assimilation. 



