For several years, migration has been attributed to climate change. People back then rely on plants and wild animals and marine life. However, periods of and cold had a great effect on the lives and development of plants and animals. Climate changes greatly affect what kind of plants will grow on a certain area (cold or hot area), thus, depends what animals will be there too. People need to go where abundant food is. When there is scarcity of food in a certain area, they are forced to move to another place where there is enough food. People back then moved out due to intense cold and intense heat. Where there is cold, they look for a warmer place, where there is intense heat; they look for a better place to cool off.