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. 
These four laws may be summarized briefly into these two 
principles: (1) 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. 
