4 
YOKKSHIRE NATURALISTS' UNION. 
climatic or physical changes, may be more satisfactorily explained by 
the compulsory migrations, due to the persistent and stern struggle 
tor existence, whose results are displayed not only by the extirpation 
of species, but by the weaker forms which have been worsted in life's 
struggle being compelled to ado})t ai^uatic life, or to seek refuge by 
the sea-shore, on mountain-toi)s, in dense woods, or on barren moors, 
the whole aspect of the plant or animal becoming more or less modified 
in accordance with the surioundings it is compelled to endure. 
Fig. 1.— Map illustrating the approximate relative degrees of dominancy of the various 
regio'is of the world. The darkest sha les indicates the most dominant areas and the graduated 
lighter tints denote the lessening dominating power of other regions. 
The influence of this competition in the evolution and advance- 
ment of every kind of organized life from man to monad is quite 
indisputable, and the erstwhile dominant families or genera whose 
metropolis is now in other countries, formerly inhabited Europe, 
but have long ago been expelled therefrom by the competition of 
superior grou])s or species -thus the lemurs, the tapirs, the giraffes, 
the hipp()})otamus, the elephants, the marsupials, the apes, the 
monkeys, etc., were once all European, but have since been scattered 
over the earth, and now live in the most distant countries, being 
replaced in our area by the development of the more advanced 
organisms which have gradually expelled them, and as competition 
acts in the way of preserving the most improved forms, each new- 
species or genus will tend to eventually take the place of its ow^n 
])arent form and also that of others less advanced. 
Dominancy in the highest degree is also testified by individual 
abundance, great plasticity or variability, activity in evolving new 
forms, as well as by geographical position and continuity of the area 
of distribution, and these attributes are the especial endowment of 
fhe inhabitants of the PalfParctic region, the phenomenon culminating 
