 The theoretical issue is whether a plausible elaborating explanation is available to underpin Marxist functional explanations. Here there is something of a dilemma. In the first instance it is tempting to try to mimic the elaboration given in the Darwinian story, and appeal to chance variations and survival of the fittest. In this case “fittest” would mean “most able to preside over the development of the productive forces”. Chance variation would be a matter of people trying out new types of economic relations. On this account new economic structures begin through experiment, but thrive and persist through their success in developing the productive forces. However the problem is that such an account would seem to introduce a larger element of contingency than Marx seeks, for it is essential to Marx’s thought that one should be able to predict the eventual arrival of communism. Within Darwinian theory there is no warrant for long-term predictions, for everything depends on the contingencies of particular situations. A similar heavy element of contingency would be inherited by a form of historical materialism developed by analogy with evolutionary biology. The dilemma, then, is that the best model for developing the theory makes predictions based on the theory unsound, yet the whole point of the theory is predictive. Hence one must either look for an alternative means of producing elaborating explanation, or give up the predictive ambitions of the theory.