1888-89.] Mr J. A. Thomson on Theory of Heredity. 
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The History and Theory of Heredity. By J. Arthur 
Thomson, Esq., M.A. 
(Read January 21, 1889.) 
The present paper has a three-fold object : — (1) to give a history 
of the theories of heredity which have been proposed by so many 
naturalists, with an appreciation of these in the light of recent 
advances ; (2) to gather together the various contributions which 
have made the modern restatement possible ; (3) to enter a protest 
against what the author believes to be the extreme position so 
firmly maintained by Weismann, to whom, however, much of the 
recent progress has been due. An historical review is necessary (in 
Britain at least) both as a contribution to the general history of the 
science, and as a basis for further construction ; the accumulating 
mass of recent literature makes a collation desirable ; the import- 
ance of Weismann’s position in relation to the Theory of Evolution 
makes criticism imperative. 
I. The Facts of Inheritance. 
It is necessary, at the outset, to summarise what are usually 
regarded as the principal facts of inheritance. (1) The general like- 
ness between parent and' offspring is a commonplace of observation, 
condensed in the familiar saying, “Like begets like.” (2) But besides 
the general resemblance, which expresses the relative constancy of 
the species, a particular similarity is often demonstrable. The 
offspring reproduces not only the general features, but often minute 
characteristics of the parent. (3) In very many instances the off- 
spring exhibits, not parental, so much as grandfatherly character- 
istics, e.g., in the familiar phenomena of atavism. (4) Without 
entering debatable ground, we must further note the fact of the 
frequent recurrence of the pathological characters of the parent in 
the constitution of the offspring. (5) But the fact in regard to the 
explanation of which most debate at present obtains, is that 
characters individually acquired by the parent as the results of 
environmental or of functional influence, certainly reappear, whether 
they be transmitted or not, in the offspring. 
Denials of these Facts. — Now, while the resemblance between 
