242 THEORETICAL BIOLOGY 



and fuller than that of any one of them. Within this sur- 

 rounding-world the fate of many thousands of individuals 

 would have to run its course ; and thus we should get a glimpse 

 into the relations between surrounding-world and species, as 

 weU as an understanding of the meaning of the differences 

 between the properties of the individual creatures. Although 

 each organism is perfect, in the sense that it exploits to the 

 full the means at its disposal, yet the perfection of the species 

 is higher, because the limits that are imposed on the individual 

 are shifted much further back. An individual cannot be black 

 and white at the same time, nor swift and sluggish, nor large 

 and small. But a species can possess and bring to realisa- 

 tion contradictory properties simultaneously, because it is 

 not bound to the function of one single framework. 



Accordingly, the species and the individual are differently 

 armed vis-a-vis of all the vicissitudes of the external world. 

 And that, along with the increase in the surrounding- world, 

 is the chief reason for the existence of the species. 



Let us assume that there were no species, but merely a 

 large number of individuals constructed in exactly the same 

 way ; a very insignificant circumstance might suffice to cause 

 all these organisms to perish ; while others furnished with 

 different properties would easily escape destruction. On 

 account of the presence within it of many different animals, 

 the species is not annihilated even if certain individuals, 

 built all alike, be lost. For the animals that survive are 

 able to replace those that have perished, since each may 

 contain, in addition to the genes for its own properties, as 

 many genes for recessive properties. So the species will 

 not find it difficult to make good the loss by crossing. 



Sexual reproduction serves not merely for the continual 

 renewal of the same individual ; for that, simple division 

 would suffice, as we see it in the unicellulars, which split in 

 two and then regenerate once more. As Jennings has shown, 



