SOME ASPECTS OF ZOOLOGY 41 



class of the animal kingdom would soon exhaust the available 

 supply of food and perish by famine. 



It follows, from this consideration, that the " Ratio of 

 Increase so high as to lead to a struggle for life and as a con- 

 sequence to Natural Selection " has not exactly the significance 

 commonly attributed to it. The fishes that swarm in the sea 

 and prey upon one another are subject to destruction at every 

 stage of their existence, and the species only maintain their 

 existence by their fertility. They produce enormous numbers 

 of eggs, which for the most part float on the surface, and afford 

 food for innumerable other animals. These passive embryonic 

 stages cannot be said to enter into competition with one another, 

 yet probably it is at this stage that the rate of destruction is 

 the highest. The newly hatched and defenceless young are 

 again a source of food and a prey to other creatures, and they 

 again can hardly be regarded as actively competing with one 

 another. It is when the highest rate of destruction is past 

 that the survivors begin to develop their adaptive characters, 

 and these promptly lead to segregation of the species, which 

 henceforth live more or less apart, as schools of mackerel, or 

 as the more solitary bottom-frequenting flounders, plaice and 

 Pleuronectids generally. The inference is that a very high 

 ratio of increase is itself an adaptation, having high survival 

 value. This point of view is different from that usually taken 

 up, which assumes that all organisms are striving to increase 

 at the greatest possible rate and that adaptation is the con- 

 sequence of the increase. 



In the essay " On the Duration of Life," which formed 

 the starting-point of his elaborately constructed theories, 

 Weismann clearly brought out the fact that, not only is there 

 a correlation between the length of life and the time and care 

 bestowed on the nurture of their young by animals, but also, 

 the higher instincts and organisation implied by this parental 

 care are associated with a diminished fecundity. Of course 

 the term " Ratio of Increase " may be taken to mean, not the 

 actual fecundity, that is to say the power of producing a given 

 number of eggs or young by any animal, but the numbers 

 which survive all the vicissitudes of youth and are able in 



