THE THEORY OF USE-INHERITANCKE. 769 
THE THEORY OF USE-INHERITANCE, 
PSYCHOLOGICALLY CONSIDERED. 
By Proressor H. Laurrz, LL.D. 
Tue large subject of the hereditary transmission of char- 
acteristics acquired during the lifetime of an individual has 
been treated from two points of view. It has been asked 
whether the effects of use and and disuse may be thus trans- 
mitted. And, again, inquiry has been made into the trans- 
mission of individual modifications resulting directly from 
the action of the environment. These questions, however, 
are very closely connected, and cannot be discussed in entire 
independence of each other. 
The biological aspect of the theory of use-inheritance is 
the most prominent. If it can be proved that structural 
and physiological characters acquired by the use or disuse 
of different parts of the organism are handed on, a similar 
principle may be applied to mental traits; and, on the other 
hand, the disproof of this principle, biologically, would lead 
us to discard it in psychology. At the same time, the sub- 
ject deserves, and demands, a separate psychological treat- 
ment. We know that a limb is strengthened by use and 
weakened by disuse; and we may ask, as a question of fact, 
apart from various theories of the mechanism of heredity, 
whether the effects.of such use and disuse are transmitted 
to descendants. On the psychological side we know, equally, 
that a benevolent or an envious disposition may be con- 
firmed by habit, and the question of transmission recurs. 
We cannot, however, answer this psychological question by 
any biological investigation; we cannot trace the nervous 
changes which accompany these altered dispositions; and 
our belief in such concomitant changes springs, not from 
direct observation, but from our conviction of a thorough- 
going correlation between the mind and the nervous system. 
When we inquire whether mental dispositions acquired or 
strengthened during a lifetime are transmitted hereditarily, 
our observation can extend only to the feelings of parent 
and child, as manifested in conduct. It is clear, therefore, 
that the psychological inquiry cannot be neglected. 
Since the appearance of Weismann’s Essays on Heredity, 
the literature of the questions raised by him has grown to so 
vast a size that only a specialist can lay claim to be fully 
acquainted with it. Without entering on the theory of 
germ-plasm, or rival hypotheses as to the working of 
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