2i6 EVOLUTION, GENETICS, AND EUGENICS 



that the various parts are more than mutually dependent, that they 

 are in some measure co-ordinated, making larger systems workable. 



What the metaphor of "the web of life" suggests. — We may use 

 the metaphor "web of life" in two ways. On the one hand. Nature 

 has a woven pattern which science seeks to read, each science following 

 the threads of a particular colour. There is a warp and woof in this 

 web, which to the zoologist usually appear as "hunger" and "love." 

 There is a changing pattern in the web, becoming more complex as the 

 ages pass; and this is evolution. But the essential idea of a web is that 

 of interlinking and ramifying. We can never tell where a thread will 

 lead to. If one be pulled out, many are loosened. This is true of 

 Nature through and through. 



The phrase "web of life" suggests another picture — the web of a 

 spider — often an intricate system, with part delicately bound to part 

 so that the whole system is made one. "The quivering fly entangled 

 in a corner betrays itself throughout the web; often it is felt rather 

 than seen by the lurking spinner. So in the substantial fabric of the 

 world part is bound to part. In wind and weather, or in the business 

 of our life, we are daily made aware of results whose first conditions are 

 very remote; and chains of influence, not difficult to demonstrate, 

 link man to beast, and flower to insect. The more we know of our 

 surroundings the more we reahse that nature is a vast system of link- 

 ages, that isolation is impossible." 



Dependence of living creatures on their surroundings. — We do 

 not know what life in principle is, but we may describe living as action 

 and reaction between organisms and their environment. This is the 

 fundamental relation — the dependence of living creatures on appro- 

 priate surroundings, and the primary illustrations of linkages must be 

 found here. The living creatures are real, just in the same sense as the 

 surroundings are real; but it is plain that we cannot abstract the living 

 creatures from their surroundings. When we try to do this they die — 

 even in our thought of them, and our biology is only necrology. 

 Huxley compared a living creature to a whirlpool in a river; it is always 

 changing, yet always apparently the same; matter and energy stream 

 in and stream out; the whirlpool has an individuality and a certain 

 unity, yet it is wholly dependent upon the surrounding currents. One 

 may push the whirlpool metaphor too far, so as to give a false sim- 

 plicity to the facts, for when vital whirlpools began to be there also 

 emerged what cannot be discerned in crystal or dewdrop — the will to 

 Uve, a capacity of persistent experience, and the power of giving rise to 



