Variation is a normal characteristic of living organisms, and the operation of the laws of chance under natural conditions maintains the stability of these respective kinds. It is necessary to prevent natural conditions in order to produce and maintain new strains of livestock and vegetables, and the new varietal characteristics would usually hinder survival in the wild state. The effect of the gene pool is noted in variations in color, including albinism and melanism. Unusual Australasian forms are discussed in the light of the fossil record. Other variables include bird life and isolation, and human disease resistance. The relationships of environment to variation are discussed in reference to animal size, climate, elevation, degrees latitude, high temperature, salinity, moisture, aridity, and geographic distribution, along with the limits that can be endured by living organisms.