Social scientists have been wary of applying Darwin's ideas. In our book Darwin's Conjecture: The Search for General Principles of Social and Economic Evolution (published 2010 by the University of Chicago Press) we argue that these misgivings are ungrounded. We show in detail that prominent objections to the idea that social evolution is Darwinian are fatally flawed. We show how the core ideas in Darwin's theory of evolution can be applied to the evolution of social and economic phenomena. Darwin himself alluded to this possibility. Other authors repeated the idea, from Walter Bagehot through Thorstein Veblen to Donald T. Campbell and Richard Dawkins. But until now the key theoretical concepts required in such a generalization have been inadequately refined. Of course the detailed mechanisms of socio-economic evolution are very different from those in the biological world. But also detailed mechanisms differ greatly within the biological sphere. Darwinism provides an abstract theoretical framework that applies to a wide range of different phenomena. Instead of drawing analogies, which are often inexact and sometimes treacherous, generalized Darwinism relies on the claim of common abstract features in both the social and the biological world; it addresses a degree of ontological communality at a high level of abstraction. This communality is captured by abstract concepts such as replication and selection. We use the term complex population systems to refer to both biological and social phenomena. By outlining the shared features of complex population systems we identify significant ontological communality. We propose that all complex population systems can be analyzed in terms of general Darwinian principles. Populations are defined by members of a type that are similar in key respects, but within each type there is some degree of variation. Entities within these populations have limited capacities to consume some materials and energy from their environment and they can process some information useful for survival. All these entities need to consume materials and energy in order to survive or minimize degradation. But because they do not have access to all environmental resources at once, these entities face an omnipresent problem of local and immediate scarcity. In short, these entities are engaged in a struggle for existence. Finally, we assume some capacity to retain and pass on to others workable solutions to problems. Retention avoids the risks and costs of learning them anew. This is the foundation for trans-generational cumulative growth of problem-solving "knowledge." It is also the basis of the Darwinian principle of inheritance, which refers to a broad class of mechanisms by which information concerning adaptations is retained or passed on through time. Examples of complex population systems are plentiful both in nature and in human society. They include every biological species, from amoeba to humans. They would also include the automatically replicating robots of science fiction. In addition, and importantly for the social scientist, they include human institutions, as long as we regard institutions as cohesive entities having some capacity for the retention and replication of problem solutions. The evolution of such a system must involve the three Darwinian principles of variation, selection and inheritance. These abstract principles do not provide all the explanatory details, but without them the explanation of evolution will be inadequate. First, there must be some explanation of how variety is generated and replenished in a population. In biology the answers involve genetic recombination and mutations. But the evolution of social institutions involves imitation, planning and other mechanisms very different from those found in biology. Nevertheless, the existence and replenishment of variety must be explained. Second, there must be an explanation for how useful information concerning solutions to particular adaptive problems is retained and passed on. In biology, these mechanisms often involve DNA. In social evolution, we may include the replication of habits, customs and routines. Some such solutions must endure and replicate, otherwise the continuing retention of useful knowledge would be impossible. Third, we must explain why entities differ in their longevity and fecundity. Some entities are more adapted than others, some survive longer than others, and some are more successful in producing offspring. Here we invoke the principle of selection. Through selection, a set of entities, a population, will gradually adapt in response to their environment. The outcomes of a selection process are necessarily neither moral nor just. There is no requirement that the outcomes of selection are necessarily optimal or improvements on their precursors. Darwinism does not assume that selection brings about globally efficient or optimal outcomes. Without the principle of selection, we have no way of explaining how some entities prevail over others. The move from the natural to the social world does not undermine the principle of selection. Some explanation is required of why some institutions enjoy greater longevity than others, why some are imitated more than others, and why some diminish and decline. As long as there is a population within which entities display variation in the acquisition of characteristics vital to survival, then Darwinian evolution will occur. But Darwinism does not provide a complete theory of everything, from cells to human society. Instead, Darwinian principles are a kind of meta-theory - an over-arching theoretical framework wherein theorists place particular explanations. Explanations additional to natural selection are always required to explain any evolved phenomenon. In our book we go on to consider examples of Darwinian processes in the social and business world. In this way we point to an agenda of study guided by the profound theoretical framework developed by Darwin over 150 years ago. Future research must show how detailed mechanisms of socio-economic evolution fit into this framework. Of course, our contribution relies extensively on the work of others. For example, in refining the concepts of selection and replication we rely extensively on recent work in the philosophy of biology, by David Hull, Elliott Sober, Robert Brandon, George Price, Kim Sterelny, Peter Godfrey-Smith and others. In one important respect we go significantly further than Darwin, by adopting the modern concept of replicator and interactor. Replicators are mechanisms that contain informational solutions to survival problems. Genes in the biological world, and habits and customs in the social world, are replicators. Interactors are relatively cohesive entities that host replicators and struggle for survival, leading to differential replication. Organisms in the biological world, and many business, political and other organizations in the social world are interactors. Some of the implications of the replicator-interactor distinction concern the evolution of complexity. We show that one of the necessary conditions for the growth of complexity is the minimization of error in the copying of replicators. Accordingly, we must account for the extraordinary growth in the complexity of human society over the last ten thousand years must in part be explained by the human capacity to store and replicate information accurately. We argue that just as biological evolution has gone through different stages in the development of different types and levels of replication, the same is true of social evolution. Each new level builds on its predecessors and invokes more sophisticated mechanisms for retaining and copying information. In human social evolution we have seen the evolution of language, rituals, writing, laws, and the institutions of science and technology. Our hope in developing this theoretical framework is that others will help us to fill in the details. Both the biological and the social worlds are immensely varied and complex and it is impossible for one theory or model to explain everything. But we have the over-arching Darwinian theoretical framework, enhanced by the modern concepts of replicator and interactor, as our guide.