Friedrich Engels Funeral Oration for Marx

Just as Darwin discovered the law of evolution in organic nature, so Marx discovered the law of evolution in human history; he discovered the simple fact, hitherto concealed by an overgrowth of ideology, that mankind must first of all eat and drink, have shelter and clothing, before it can pursue politics, science, religion, art, etc, and that therefore the production of the immediate material means of subsistence and consequently the degree of economic development attained by a given people ...