156 ANIMAL BEHAVIOUR 



56. ON THE EXCESS-VALUES OF THE URGES OF LIFE 

 The results of animal behaviour are often in excess of those 

 that are necessary for normality. This we consider more in 

 detail. 



i. Assimilation. The expenditure of energy by the animal 

 depletes its tissues of oxidizable material. If it grows or repro- 

 duces this depletion is again the case. Therefore there must be 

 continual assimilation of materials into the body. This neces- 

 sitates the behaviour of obtaining, and eating food. There is 

 an urge to assimilate which is felt as hunger and eating satisfies 

 that urge. Normality would be attained when just so much 

 food as would provide for the necessary assimilation is ingested, 

 but as a rule an animal which is hungry will eat more than this 

 and may fatten (to its disadvantage), or may merely excrete the 

 excess of foodstuffs eaten. In the healthy animal that is of 

 constant weight and in nitrogenous equilibrium there is normality 

 as regards assimilation. Of itself, however, the animal may 

 *' over-eat " because of the pleasure of doing so. This is excess- 

 value of assimilation. In civilized man it is represented by the 

 banquet, etc. 



ii. Growth. Excess is represented by corpulence, or in a 

 sinister quality by the malignant tumour. 



Hi. Reproduction. Normality may be taken as given by that 

 density of individuals, in any region, which is constant — when, 

 on the average, as many are born and live to reproductive age, 

 as there are deaths. Actually there may be an enormous pre- 

 ponderance of births over the deaths of reproductively mature 

 individuals (and there will, of course, be a correspondingly high 

 death-rate of individuals that never became reproductively 

 mature). This is excess-value of reproduction. 



iv. Reproductive Behaviour. Both in man and the higher 

 mammals and birds there is complex behaviour anticipatory of 

 the essential reproductive act — which is the conjugation of the 

 gametes. This behaviour is now an extraordinarily large part 

 of general human activity — that is, it has marked excess-value. 

 It is represented by '' lover's poetry," erotic, and much 

 *' romantic " literature, prostitution, sexual perversion, etc. 



V. Self -preservation. Normality is, perhaps, represented by 



