Levels of organization are structures in nature, usually defined by part-whole relationships, with things at higher levels being composed of things at the next lower level. Typical levels of organization that one finds in the literature include the atomic, molecular, cellular, tissue, organ, organismal, group, population, community, ecosystem, landscape, and biosphere levels. References to levels of organization and related hierarchical depictions of nature are prominent in the life sciences and their philosophical study, and appear not only in introductory textbooks and (...) lectures, but also in cutting-edge research articles and reviews. In philosophy, perennial debates such as reduction, emergence, mechanistic explanation, interdisciplinary relations, natural selection, and many other topics, also rely substantially on the notion. -/- Yet, in spite of the ubiquity of the notion, levels of organization have received little explicit attention in biology or its philosophy. Usually they appear in the background as an implicit conceptual framework that is associated with vague intuitions. Attempts at providing general and broadly applicable definitions of levels of organization have not met wide acceptance. In recent years, several authors have put forward localized and minimalistic accounts of levels, and others have raised doubts about the usefulness of the notion as a whole. -/- There are many kinds of ‘levels’ that one may find in philosophy, science, and everyday life—the term is notoriously ambiguous. Besides levels of organization, there are levels of abstraction, realization, being, analysis, processing, theory, science, complexity, and many others. In this article, the focus will be on levels of organization and debates associated with them, and other kinds of levels will only be discussed when they are relevant to this main topic. (shrink)

The idea of reduction has appeared in different forms throughout the history of science and philosophy. Thales took water to be the fundamental principle of all things; Leucippus and Democritus argued that everything is composed of small, indivisible atoms; Galileo and Newton tried to explain all motion with a few basic laws; 17th century mechanism conceived of everything in terms of the motions and collisions of particles of matter; British Empiricism held that all knowledge is, at root, experiential knowledge; current (...) physicists are searching for the GUT, the “grand unified theory,” that will show that at very high energies the electromagnetic and the weak and strong nuclear forces are fused into a single unified field. Some of these projects are clearly ontological in nature (Leucippus and Democritus), others are more methodological (mechanism), and still others strive for theoretical simplification (the projects of Galileo and Newton or the search for a GUT). Nevertheless, as they all aim at revealing some kind of unity or simplicity behind the appearance of plurality or complexity, they may all be regarded as (attempted) reductions. (shrink)