Response by living creatures, in the form of novel or intensified efforts, to their environmental difficulties and limitations. This process is characterized by continuing, and often painful or fatal, clashes both between the living creatures and with their environments. The struggle is aggravated by the tendency of any species towards over-population, by the dependency of members of the population on one another and on other species, and by unpredictable changes in the environment. The struggle is thus not limited to intraspecific competition. It takes place between both fellow-organisms of the same species and between organisms of very different natures.
It is a mistake to consider that the struggle is necessarily directly competitive, sanguinary, and results in the immediate elimination of one of the parties. It may often be accurately described as an endeavour after well-being. In face of difficulties and limitations, one kind of organism may intensify competition, another may exhibit more elaborate parental care or greater mutual aid, another may adopt some form of parasitism and another may change its habitat. Half-understood technical concepts from biology have frequently encouraged inappropriate conclusions. The universal struggle in nature has been erroneously used to vindicate internecine competition and warfare among men.