
I! 
natural and social evolution by the variation of both factors. In 
plant life the ratio was affected mainly by alterations in the fitness 
of the organism, but instances were not wanting in which the 
organism likewise modified its environment. Such instances 
were mostly seen in co-operation between various organisms. 
Lichens are a mutual provident society of fungi and algae. The 
bacteria of the nodules of leguminous plants pay for their 
maintenance by fixing nitrogen from the soil and air, and 
supplying it to the plants. The beech thrives only when a 
mantle of the fungus mycorrhiza developes over its roots; the 
fungus, being fed by the beech, in return supplies it with certain 
salts, thereby dispensing with unnecessary expenditure of force 
on added rootlets. Again, between plants and animals there are 
many instances of useful partnership. Certain seaweeds are 
attached to the shells of marine crabs, the crab thereby simulating 
the appearance of a rock, whilst the seaweed secures multiplied 
Opportunities of receiving food. Ants tenanting the “ bull’s horn” 
acacia tree obtain food and shelter from it while they defend it 
from enemies. Even beetles inhabiting manure heaps help each 
other in rolling up pellets of dung and burying them as larval 
food with eggs embedded in them. Still better known are the 
co-operative efforts to control their environment displayed by 
such animals as the bee, the ant, the beaver, &c. 
In the evolution of man, the intelligent power to alter 
environment played a supremely important part, because he alone 
appeared to be capable of improving on the experience of his 
forbears. Although certain orangs pelted passers-by with nuts, 
and the chimpanzee cracked his nuts with a stone, man was the 
only animal employing tools of increasing complexity for his 
wants. He alone clothed himself and cooked his food. He had 
learnt also to press into his service the forces of nature and the 
organic modifications of plants and animals, as in cultivated 
cereals and domesticated animals. Environment for one class of 
animal was the sime for other classes ; hence the primitive method 
_ adopted by the strong in modifying this environment consisted 
largely in destroying the weak and appropriating their property. 
But that was not the only method employed, as instances already 
_ quoted clearly showed. In the various forms of co-operation seen 
_in animals, there was a constant succession of acts which in man 
were counted as honesty, fidelity, justice, mercy, sympathy, and 
benevolence. In some cases, e¢.g., parental devotion, the act 
‘was done from an innate altruistic pleasure, thus showing ‘‘ they 
- follow the law, but know not the doctrine.” There could be but 
little doubt but that the mitigation of the tendency to mutual 
destruction originated in a sense of the net advantage to be 
derived by the individual from mutual help. Upon this were 
_ based the foundations of society, and social evolution consisted 
‘substantially in its development. 
