INTRODUCTORY 13 



by external influences is continued throughout life. 

 Different creatures differ greatly in their susceptibility, but 

 they are all in the grip of a complex environment which 

 acts on them in rough or in subtle ways. Whether we 

 think of the seasons or the climate, the soil or the sea, we 

 find that this environment is intricately variable. Indeed 

 every kind of plant and animal is continually passing into 

 a new environment of chemical, mechanical, dynamic, and 

 animate influences which play upon it. All through the 

 ages this has been going on; living creatures have been, 

 as it were, ceaselessly passing over a series of anvils on 

 which the hammers of external influences play, with tunes 

 of ever-increasing complexity. It is evident that every 

 increase in the fulness of life implies additional complexity 

 in the incidence of external forces. Every increase in 

 locomotive power, for instance, increases the multiplicity 

 and multiformity of action and reaction between the 

 animal and its surroundings. 



Part of the Biology of the Seasons, then, consists in 

 studying the dints made on living creatures by something 

 unusual in the play of the inanimate hammers by some 

 change in the surge of the wave, the swish of the wind, 

 the salinity of the water, the composition of the soil, the 

 humidity of the air, the temperature, the illumination, and 

 so on. The organism is continually running the gauntlet 

 of environmental forces, which may induce responses or 

 modifications. These may be defined as structural changes 

 in the body of an individual, directly induced by changes in 

 function or in environment, which transcend the limit of 

 organic elasticity, and thus persist after the inducing 

 conditions have ceased to operate. Thus the tanning 

 which follows prolonged sun-burning in the Tropics may 

 persist as a permanent modification throughout the rest 

 of the individual life. 



