Darwin believed that animals compete for such things as food and water with other species and within their own species and the varieties that are most capable to do this successfully were naturally selected and eventually formed new species and that this mechanism explains the origin of species. Marx believed that social classes compete with each other ie the working class with the bourgeoisie with each trying to fulfil their needs the bourgeoisie for maximum profits and the working class for better wages and working conditions and eventually for the fruits of their labour to be used for socially useful purposes not just to enrich a few at the expense of the many so this is a revolutionary process.