Marx called a social pattern “contradictory” if the conditions of its maintenance are also key ingredients for its demise. The science of ecology, too, studies patterns the conditions for whose maintenance are also key ingredients for their demise. The historical materialist notion of contradiction has a close counterpart in the ecological notion of succession. Succession is a process by which the structure of a biological community—both niche structure and species structure—changes as a result of each species' modification of the habitat. Just by living, each species members alters its environment, and in non-climax communities these effects, summed over all living things, constitute disequilibria. The habitat changes, and with it the niche structure. Gradually the species structure of the community changes. Each seral stage, with its distinctive species structure, requires for its maintenance the ongoing existence of living members of each species in the structure; yet this condition is the key ingredient for succession, for the demise of the seral stage. Succession results, in effect, from contradictions that are present in each seral stage. (For an illustrative example of seral stages and biological succession, see the Appendix.)