Questions Evolution Does Not Answer 
geology furnishes evidence of the 
existence of transitional forms, or 
gives proof of a gradual and uni¬ 
form development from simple 
forms to complex organic life by 
means of resident forces. 
3. Another difficulty that pre¬ 
sents itself is the fact that there is 
a remarkable difference between 
varieties and species with respect 
to fertility when crossed. As a 
rule, varieties, when crossed, are 
fertile, and their progeny continue 
to be so, while species, when crossed, 
are usually infertile, and where 
hybrid offspring are produced they 
are absolutely infertile. (Wallace, 
“ Darwinism, ” p. 153; Darwin, 
“Origin of Species,’’ p. 23.) This 
is true even in such closely allied 
species as the horse and the ass. 
“The mule still stubbornly flouts 
the theory of the transmutation of 
species.” 
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