INFLUENCE OF ENVIRONMENT 113 



reflect that the infinitely diversified but slowly changing environment 

 in which the animals of each race have successively been placed, 

 has involved each of them in new needs and corresponding alterations 

 in their habits. This is a truth which, once recognised, cannot be 

 disputed. Now we shall easily discern how the new needs may have 

 been satisfied, and the new habits acquired, if we pay attention to the 

 two following laws of nature, which are always verified by observation. 



First Law. 



In every animal which has not passed the limit of its develo'pment, 

 a more frequent and continuous use of any organ gradually strengthens, 

 develops and enlarges that organ, and gives it a power proportional to 

 the length of time it has been so used ; while the permanent disuse of 

 any organ imperceptibly iveakens and deteriorates it, and progressively 

 diminishes its functional capacity, until it finally disappears. 



Second Law. 



All the acquisitions or losses wrought by nature on individuals, through 

 the influence of the environment in which their race has long been placed, 

 and hence through the influence of the predominant u^e or permanent 

 disuse of any organ ; all these are preserved by reproduction to the new 

 individuals which arise, provided that the acquired modifications are 

 common to both sexes, or at least to the individuals which produce the 

 young. 



Here we have two permanent truths, which can only be doubted 

 by those who have never observed or followed the operations of nature, 

 or by those who have allowed themselves to be drawn into the error 

 which I shall now proceed to combat. 



Naturalists have remarked that the structure of animals is always 

 in perfect adaptation to their functions, and have inferred that the 

 shape and condition of their parts have determined the use of them. 

 Now this is a mistake : for it may be easily proved by observation 

 that it is on the contrary the needs and uses of the parts which have 

 caused the development of these same parts, which have even given 

 birth to them when they did not exist, and which consequently have 

 given rise to the condition that we find in each animal. 



If this were not so, nature would have had to create as many different 

 kinds of structure in animals, as there are different kinds of environ- 

 ment in which they have to live ; and neither structure nor environ- 

 ment would ever have varied. 



This is indeed far from the true order of things. If things were 

 really so, we should not have race-horses shaped hke those in England ; 



