BIOLOGICAL EVOLUTION 57 



The four laws of organic evolution as formulated by Lamarck 

 in his latest work are as follows: 



First law: Life, by its proper forces, continually tends to increase the 

 volume of every body which possesses it, and to increase the size of its parts, 

 up to a limit which it brings about. 



Second law: The production of a new organ in an animal body results 

 from the supervention of a new want (besoin) which continues to make itself 

 felt, and of a new movement which this want gives rise to and maintains. 



Third law: The development of organs and their power of action are con- 

 stantly in ratio to the employment of these organs. 



Fourth law: Everything which has been acquired, impressed upon, or 

 changed in the organization of individuals, during the course of their life is 

 preserved by generation and transmitted to the new individuals which have 

 descended from those which have undergone these changes. 1 



These four laws may be summarized briefly into these two 

 principles: (i) the active response of an organism by way of 

 variation to a felt need of adjustment to its environment, and 

 (2) use and disuse inheritance. The first issues easily into the 

 theory of an active life-principle or " bathmic force " as formu- 

 lated by Nageli, Ratzenhofer and Ward, while the second has been 

 the chief point of contention among biologists since Weismann's 

 experiments on mice. 



After pointing out the function of instinct in the lower orders 

 Lamarck differentiates the higher in a way to lay the biological 

 foundation of the concept of active adaptation. " It is not the 

 same in animals which, besides a nervous system, have a brain, 

 and which make comparisons, judgments, thoughts, etc. These 

 same animals control more or less their power of action according 

 to the degree of perfection of their brain; and although they are 

 strongly subjected to the results of their habits, which have modi- 



1 Packard, Lamarck, p. 346. "Every want felt produces an emotion in the 

 inner feeling of the individual which experiences it; and from this emotion of the 

 feeling in question arises the force which gives origin to the movement of the parts 

 which are placed in activity. . . . Thus, in the animals which possess the power 

 of acting, the force productive of movements and actions, the inner feeling, 

 which on each occasion originates this force, being excited by some need, places in 

 action the power of force in question; excites the movement of displacement in the 

 subtile fluid of the nerves which the ancients called the animal spirits; directs 

 this fluid toward that of its organs which any want impels to action; finally, makes 

 this same fluid flow back into its habitual reservoirs when the needs no longer 

 require the organ to act." Ibid., p. 330. 



