Traditionally, epistemologies have been human-centred, while typically presenting themselves as objective 'views from nowhere' applicable to all knowers. One consequence of this is that the question, 'How is knowledge possible?', has been either implausibly answered or ignored - except by naturalistic epistemologies, and in particular, evolutionary, biosemiotic, and autopoeitic approaches. These approaches, recognizing that humans are not the only knowers, perceivers, cognizers and rememberers in nature, ask instead, 'How does nature make knowledge possible?' thereby reconceiving epistemology as study of the cognition and experience of living, embodied, interacting and inter-signifying natural beings. Nonetheless, their insights into how nature makes knowledge (and other epistemological achievements) possible, while instructive, typically are incomplete - in most cases because key aspects of the peculiar physical/causal dynamics of cognitive processes and their causal/functional roles in the lives of organisms, are insufficiently considered. This paper seeks to redress this situation, to provide a clearer understanding of how nature makes knowledge (and other epistemological processes and achievements) possible. The argument draws upon insights of the approaches mentioned, and upon studies of biological hierarchy, natural emergence, complex causal dynamics and hierarchically structured causal processes, to show that nature's 'inventions' of non-linear causation and cybernetic process-modulation led to the emergence of novel systems whose sensitivity to ultra-low-energy signals (for example, just a few molecules of a chemical compound) radically enhances their viability by producing a non-linear hierarchically ordered cascade of adaptive activity peculiarly associated with the signal type. This is biosemiosis. It is argued that the unique causal character of biosemiotic processes is not only their physical 'signature', but is essential to subsequently emergent cognitive processes and achievements and their functions, and indeed to the biological functions of the organic processes that make life possible. This is a further reason (if further reason were needed) for holding biosemiosis to be, ontologically, a natural kind. Indeed, an understanding of the distinctive causal/functional character of biosemiosis is the key to understanding how nature makes possible not only knowledge (and all other epistemological processes and achievements) but also, by those semiotic means, life itself.