In the long evolutionary process, food scarcity has always been the primary threat to human beings. Due to the uncertainty of food supply and the inability to preserve food for a long time, human beings have been living a full and hungry life and can maximize the effective use of food Of individuals have survival advantages. After experiencing repeated famine selections, individuals with survival advantages and the genes in their bodies are retained by natural selection. These genes can stimulate a large amount of insulin secretion after a full meal, thereby maximizing Limit the conversion and use of glucose in the blood. Although the cost of doing so may lead to obesity, the survival threat caused by its harm to the body is not manifested until after middle age, and for most of human history Here, the average life expectancy of a person is less than 30 years. The text is intended to explain:. ['The living environment of ancient people is completely different from modern people.', 'The human physiological structure is the result of natural selection.', 'Food scarcity is the number one issue for humans in the long run.', 'Obesity is associated with dominant genes in human survival and reproduction.']