TAYLOR : DOMINANCY IN NATURE. 
13 
than at the present time, as the snow-line at the period of greatest 
cold was never more than 1,200 metres lower than its position at the 
present day, and temperature being proved to diminish half a degree 
for every 100 metres of elevation. 
The great aggregation in this country and in Europe during 
Pliocene and Pleistocene times of what are now tropical and arctic 
genera and the acknowledged general intermingling of the fossilized 
relics of reindeer, mammoth, lion, hyaena, etc., can scarcely be 
explained otherwise than by the acceptance of the suggestion that 
the climate at that period was not an extreme one, and that the 
extinction of species or their restriction at the present day to arctic 
or torrid regions is the result of competition with the superior forms 
and demonstrates that although species in course of ages become 
adapted to circumstances or hardships inseparable from the regions 
they may have been compelled to occupy yet we may be assured that 
the adoption of the hard life of the arctic regions was not a voluntary 
but an entirely compulsory act. 
In mammals, the highly organized tiger is capable of enduring great 
ranges of temperature, and although long regarded as a typical 
resident of the torrid plains of India, is nevertheless a northern 
animal enduring the harsh, intensely cold and rigorous winters of 
Siberia; indeed, it is only within the historic period that the tiger has 
penetrated into India, where it was previously unknown, so that its 
present range extends from the torrid zone to the Arctic circle. 
Dr. Scharff has also shown how little climate may affect distribution 
or dispersal, pointing out that although the fresh-water Tortoise 
{Emys oi'hiciilarls) is retreating southward in France and is common 
in Spain and North Africa, it is distinctly advancing northward in 
Russia and now inhabits as far north as St. Petersburg, and similar 
examples can be cited in almost every department of natural history. 
All living organisms are subject to variation, which is the response 
of the organism to the features of the environment, and such 
response always tends to adaptation or to adaptability. Adaptability 
confers the power of accommodation to a variety of somewhat 
different circumstances, perhaps due to a greater perfection of the 
physiological processes. It is the highway of progress, and is 
inverse to Adaptation or structural modihcations to accord with 
peculiar and strikingl}^ different environments, so that animals or 
plants which have reached a high degree of adaptive specialization, 
and acquired a strict correlation in structure to a more or less 
restricted mode of life, as the adoption of subterrane in or aquatic 
life, parasitic habits, etc., to which the structurally njodified species 
are thenceforth necessarily restricted, as they thereby become less 
capable than before of further modifications to harmonize with any 
profound changes in their environment ; thus high or excessive 
specialization, by limitingthe power of modification to other conditions, 
is a retrograde process tending to degeneracy, and is an evidence of 
their failure in life's struggle. 
