In the history of human development, "Learning to use fire" Was undoubtedly a very important point, as through the manipulation of fire, human beings were able to process various ingredients in nature into easily digestible and absorbable cooked food, to exert a powerful deterrent on other animals, to dispel darkness and cold, to harvest light and warmth, and thus step by step, a glorious civilisation has been created.

The existence of reproductive isolation, so that these situations can not occur, even if there are some individuals of different species sometimes complete the mating, but they generally can not produce offspring, or produce offspring can not continue to reproduce

In fact, the earth's crust itself is a natural source of minerals, many soil and rocks contain a certain amount of salt, careful observation of cattle and sheep should know, cattle and sheep in the grass, but also often "eat soil" or lick the stone, they do so, in fact, the purpose is to obtain the salt