OF SPECIES 43 



Moreover, we must remember that the records of his observations, 

 and the notes of facts which he has been able to register, only extend 

 back a few thousand years ; which is a time infinitely great with 

 reference to himself, but very small with reference to the time occupied 

 by the great changes occurring on the surface of the earth. Every- 

 thing seems to him to be stable in the planet which he inhabits ; 

 and he is led to repudiate the signs which exist everywhere in the 

 monuments heaped up around him, or buried in the soil which he 

 tramples underfoot. 



Magnitudes are relative both in space and time : let man take that 

 truth to heart, and he will then be more reserved in his judgments 

 on the stability which he attributes to the state of things that he observes 

 in nature. (See the Appendix, p. 141, of my Recherches sur les corps 

 vivants.) 



In order to admit the imperceptible changing of species, and the 

 modifications which their individuals undergo according as they 

 are forced to change their habits and contract" new ones, we are 

 not reduced to a mere consideration of the very short spaces of 

 time comprised in our observations ; for, in addition to this induc- 

 tion, a number of facts collected many years ago throw enough light 

 on the question to free it from doubt ; and I can now affirm that our 

 observations are so far advanced that the solution sought for is 

 patent. 



Indeed not only do we know the results of anomalous fertilisations, 

 but we also now know positively that a compulsory and sustained 

 alteration in the habitats and manner of life of animals works after 

 a sufficient time a very remarkable mutation in the individuals exposed 

 to it. 



Consider the animal which normally lives in freedom in plains 

 where it habitually exerts itself by swift running ; or the bird which 

 is compelled by its needs to pass incessantly through large spaces 

 in the air. When they find themselves imprisoned, the one in the 

 dens of a menagerie or in our stables, the other in our cages or back 

 yards, they undergo in course of time striking alterations, especially 

 after a succession of generations in their new state. 



The former loses a great part of his swiftness and agility ; his body 

 thickens, the strength and subtleness of his Mmbs diminish, and his 

 faculties are no longer the same ; the latter becomes heavy, can 

 scarcely fly, and takes on more flesh in all his parts. 



In Chapter VI. of this Part I., I shall have occasion to prove by 

 well-known facts the power of changes of conditions for giving to 

 animals new needs, and leading them on to new actions ; the power 

 of new actions when repeated to induce new habits and inclinations ; 



