v] LATER PROGRESS 115 



things if left to themselves would multiply in rapid 

 geometrical ratio, then change in the status quo is 

 inevitable. A state of equilibrium may for a time 

 exist, but every balanced organism is as it were 

 pressing against every other, and a change in one 

 means a rearrangement of them all. 



The correlated evolution of weapons of oifence 

 and defence in naval warfare is closely similar, though 

 simpler far. The leaden plum-puddings were not un- 

 fairly matched against the wooden walls of Xelson's 

 day. Halfway through the century, when guns had 

 doubled and trebled their projectile capacity, up 

 sprang the "Merrimac" and the "Monitor," secure in 

 their iron breast-plates ; and so the duel has gone 

 on, till now, though our guns can hurl a third of 

 a ton of sharp-nosed steel with dynamite entrails 

 for a dozen miles, yet they are confronted with twelve- 

 inch armour of backed and hardened steel, water- 

 tight compartments, and targets moving thirty miles 

 an hour. Each advance in attack has brought 

 forth, as if by magic, a corresponding advance in 

 defence. 



With life it has been the same : if one species 

 happens to vary in the direction of greater in- 

 dependence, the inter-related equilibrium is upset, 

 and cannot be restored until a number of competing 

 species have either given way to the increased 

 pressure and become extinct, or else have answered 



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