EVOLUTION. 81 
than others. These are sometimes termed re-foten/, and, as a general 
rule, the male is probably pre-potent over the female. A peculiar form 
of heredity of very doubtful occurrence is 7eZegony. If ashigh-bred 
bitch have a litter to a mongrel it is a commonly accepted tradition 
amongst breeders that future litters, although to high-bred dogs, will be 
contaminated by mongrel characters. There is at present no definite 
evidence for the occurrence of telegony. 
But heredity is not confined to parents or others of the preceding 
generation. Many structural characters are transmitted to the second 
generation leaving the intermediate generation apparently unaffected. 
Insanity is a remarkable instance of this. 
Lastly, an individual may exhibit characters which resemble its more 
remote ancestors. These characters are, of course, variations from the 
point of view of the parents and are often termed a¢avistzc. 
The term Reversion is also used to describe this phenomenon as well 
as the wider return of a whole species to ancestral structure (see Colusa). 
Evo.ution.—If we apply the principle of heredity to 
the whole animal kingdom we are led to explain the 
structural similarity of genera, orders, classes, and phyla as 
due to a common descent from the same early types. The 
process of descent with modification is called Lvolwtion, 
and hence an evolutionist is one who holds that all living 
animals are genetically connected in the past. 
Assuming this to be the case, how can this descent or. 
evolution have been effected? If we are able to show that 
one species can, under certain conditions, evolve into 
another, the same argument will apply to the higher grades, 
such as genera, orders, &c. If there were no variation, 
each generation of a species would by heredity be like its 
predecessor and no structural change could be effected. 
But we have seen that, owing to variation, the offspring 
never quite resembles its parents, and it is evident that 
if these differences could be accentuated and made per- 
manent, an eventual transformation of the species could 
be effected. 
Darwin was the first to show that there are certain 
conditions in nature which make this actually possible. 
Starting with the first principle of variation, as stated 
above, he went on to show that all animate nature tends to 
reproduce itself at a far higher rate than the available means 
of subsistence. This is the direct cause of the struggle for 
existence. Every animal in nature has to struggle for its 
very means of subsistence with other animals and above all 
M. 7 
