It is, however, certain that whenever any animal or plant is largely propagated constitutional variations will arise, and some of these will be better adapted than others to the climatal and other conditions of the locality.
There is reason to think, however, that it is the want of soil rather than climatal conditions that checks the upward extension of the alpine flora.
The mean annual temperature of this region differs little from that of the British Islands; but the climatal conditions are widely different.
Many writers take the growth of grain as the characteristic of the mountain region; but so many varieties of all the common species are in cultivation, and these have such different climatal requirements, that they do not afford a satisfactory criterion.
Its animals and plants have a special character suited to the peculiar climatal conditions, more closely allied to those of the adjacent northern Siberian tract than of the other bordering regions.
There is no positive evidence that the influence of new climatal conditions on the parents has any tendency to produce variations in the offspring better adapted to such conditions.
The impulse to migrate, that is to say, the calling forth of specific activities by climatal or other presentations, appears to be instin tive; whether the direction of migration is in like manner instinctive is a matter of uncertainty; and, if it be instinctive, the nature of the stimuli and the manner in which they are hereditarily linked with responsive acts is unexplained.