Originally published in 1977, Physiological Variation and its Genetic Basis. The editor of this volume, and organizer of the symposium on which it is based, was well aware that the enterprise represented an excursion into difficult, and at the time, largely unknown and even dangerous territory. Nevertheless, so fundamental are physiological responses and attributes for the efficient and adaptive functioning of the human organism that the need to understand the causes, sources and limits of their variation, both temporal and populational, pressed heavily on the human biologist. None of the contributors to this topic was so naïve as to assert dogmatically that for the polygenic systems that were believed to underly the majority, if not all, physiological characteristics, the observed variance could be separated into fixed genetic and non-genetic components. As the papers show, it is the essence of these characters that they were highly responsive to environmental change, in both the short and long term. The variable intensity of expression of these characters would of necessity be reflected in a changing relationship between acquired and in-born factors in determining differences in response between individuals within a group subject to a range of environmental exposure. This, in fact, constituted the central problem in the analysis of physiological variability and is the major theme running through this volume. Today it can be read in its historical context.