The scope of this paper is the relationship between Marxism and science, and I shall deal principally with biology, both because it is the science that has been most affected by the impact of Communism, and because it is the one with which I am best acquainted.

To begin, we must go back to the writings of Marx and more particularly of Engels, who was, much preoccupied with scientific questions. It is convenient to distinguish three groups of ideas in these writings, which may be described as materialistic, dialectical and ethical. In common with those whom Marxists call vulgar materialists, people like Büchner and Moleschott, Marx and Engels affirmed that mind is an epiphenomenon of matter—the Marxists say a reflection of matter; they are therefore realists asserting that matter exists independently of human cognition; they believe in strict causal determinacy operating according to physical law; and they deny that God exists. The dialectics comes from Hegel but most of the fundamental notions occur in the Greeks. The most important dialectical principles are firstly, the unity of opposites, which asserts the fundamental interrelatedness of all the objects composing the physical universe, secondly, the idea that change and development follow from the conflict of dialectical opposites, and thirdly, the notion that qualitative change supervenes upon the accumulation of quantitative, changes. The relation of the preceding notions to the ethical tenets of Marxism has always been obscure. For the present purpose two only of the latter need be considered, the notion that knowledge should be utilised for social well-being, and the notion, seldom explicitly stated but constantly implied, of equality in rights between all sorts of human beings. These two notions have obvious religious affiliations, which however need not be discussed here.