the words "evolution", "fact" and "theory" has several meanings in different contexts. Evolution means CHANGE over time, as in stellar evolution. In biology it refers to observed changes in organisms, to their descent from a common ancestor, and at a technical level to a change in gene frequencyover time; it can also refer to explanatory theories (such as Charles Darwin's theory of NATURAL selection) which explain the mechanisms of evolution. More individuals are produced each generation than can survive.Phenotypic variation exists among individuals and the variation is heritable.Those individuals with heritable traits better suited to the environment will survive.When reproductive ISOLATION occurs new species will form.Another important evolutionary THEORIST of the same period was the Russian geographer and prominent ANARCHIST Peter Kropotkin who, in his book Mutual Aid: A Factor of Evolution(1902), advocated a conception of Darwinism counter to that of Huxley. His conception was centred around what he saw as the widespread use of co-operation as a survival mechanism in human societies and animals