We are driven to survive by our genes and via competitive and selfish natural selection; we follow our own self-interest in order to survive and procreate; genes that adapt more quickly and better to the competitive world survive at the expense of the others, and so forth. The state of nature is a Hobbesian nightmare of there being "no society; and which is worst of all, continual fear, and danger of violent death; and the life of man, solitary, poor, nasty, brutish, and short."
It need not always be a war of extermination such as in the relations between men and morbific microbes. Reason has demonstrated that, for man, the most adequate means of improving his condition is social cooperation and division of labor. They are man's foremost tool in his struggle for survival.