The Making of Species 
considerable part in the making of new species, 
inasmuch as they may, so to speak, pave the way 
for mutations. 
We are now in a position to consider the 
exceedingly difficult question of inheritance. We 
know that offspring tend to resemble their 
parents, but that they are always a little different 
both from either parent and from one another. 
How are we to account for these phenomena? 
What are the laws of inheritance, whereby a 
child tends to inherit the peculiarities of its 
parents, and what are the causes of variation 
which make children differ zz¢er se and from 
their parents? 
Scores of theories of inheritance have been 
advanced. It is scarcely exaggerating to assert 
that almost every biologist who has paid much 
attention to the subject has a theory of inherit- 
‘ ance which differs more or less greatly from the 
theory held by any other biologist. 
As regards the phenomena of heredity we may 
say Zot homznes tot sententia. 
For this state of affairs there is a good and 
sufficient reason. We are not yet in possession 
of a sufficient number of facts to be in a position 
to formulate a satisfactory theory of inheritance. 
A complete theory of heredity must explain, 
among other things, the following phenomena :— 
1. Why creatures show a general resemblance 
to their parents. 
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