CHAPTER VII 
THE INHERITANCE OF ACQUIRED CHARACTERS AS 
A FACTOR IN EVOLUTION 
LaMARCK’S THEORY 
One of the most striking and peculiar characteristics of 
living things is that through use a part is able to carry out 
a particular function better than before, and in some cases 
the use of the part leads to its increase in size. Conversely, 
disuse leads to the decrease of a part in size. We are per- 
fectly familiar with this ptocess in ourselves as applied to our 
nervous system and muscles. 
It is not surprising that the idea should have arisen that, 
if the results of the use of a part are inherited by the next 
generation, the adaptation of organisms might be explained 
in this way. The presence of the organs of touch, in those 
parts of the body that are more likely to come into contact 
with foreign bodies, offers a striking parallel to the perfecting 
of the sensation of touch that can be brought about through 
the use of any part. The development of eyes only on the 
exposed parts of the body, as on the tentacles of the seden- 
tary annelids, or along the margin of the mantle of a bivalve 
mollusk, suggests that there may be some direct connection 
between their presence in these regions and the effect of 
light on the parts. In fact, ever since the time of Lamarck, 
there have been many zoologists who have claimed that many 
of the adaptations of organisms have arisen in this way, that 
is, through the inheritance of the characters acquired through 
use. In general this theory is summed up in the phrase, 
“the inheritance of acquired characters.” 
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