CORRESPONDENCE. 
On THE USE OF THE ‘TERMS “ HEREDITY” AND “ VARIABILITY.” 
To the Editor of the American Naturalist : 
Str, — The necessity of an accurate terminology in the discussion 
of such an abstruse and complicated subject as the evolution phi- 
losophy has always been recognized. Every one is satisfied to have 
each writer coin as many new words, or to re-define as many old ones, 
as the discussion of his subject demands. And so we have numerous 
technical terms, as “ germ- -plasm, ” “idioplasm,” “ gemmule,” “ stirp,” 
“id,” “biophore,” “diplogenesis,” etc. It is, therefore, the more 
surprising to find so many really serious fallacies and disagreements 
creeping into evolutionary discussion through the equivocal use of 
such common terms as “ heredity ” and “ variability.’ 
These two words have been often, perhaps usually, regarded as 
antonyms. Heredity and variability have been treated as two dia- 
metrically opposing laws. Even when the opposition was not so 
much emphasized, they have been treated as two separate and 
sharply distinguished principles. Darwin treats them so. Weismann 
follows a similar usage, and, in general, the uncritical custom follows 
the same line. But this investment of the terms “heredity” and 
“variability ” with two sharply contrasted meanings is essentially 
illogical. This is not a new discovery by any means, for it will be 
found on examination, I think, that the leading writers on evolu- 
tion topics have shrunk, consciously or Bacon es from bringing 
these terms into conflict at any critical point. 
The beginning of the difficulty has been in the assumption that 
organic life began under the absolute dominion of the law of heredity. 
Later, according to this assumption, variability crept in, and the 
course of organic reproduction departed farther and farther from the 
rigid line of heredity. Bailey has controverted this assumption in his 
Survival of the Unlike by another equally gratuitous assumption. The 
law of heredity is said to be that like begets like ; but Bailey asserts 
that, in the original and normal course of organic reproduction, “unlike 
begets unlike.” Of course neither statement is absolutely true; but 
if both are properly qualified they acquire practically identical mean- 
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