Natural selection is commonly seen not just as an explanation for adaptive evolution, but as the inevitable consequence of “heritable variation in fitness among individuals”. Although it remains embedded in biological concepts, such a formalisation makes it tempting to explore whether this precondition may be met not only in life as we know it, but also in other physical systems. This would imply that these systems are subject to natural selection and may perhaps be investigated in a biological framework, where (...) properties are typically examined in light of their putative functions. Here we relate the major questions that were debated during a three-day workshop devoted to discussing whether natural selection may take place in non-living physical systems. We start this report with a brief overview of research fields dealing with “life-like” or “proto-biotic” systems, where mimicking evolution by natural selection in test tubes stands as a major objective. We contend the challenge may be as much conceptual as technical. Taking the problem from a physical angle, we then discuss the framework of dissipative structures. Although life is viewed in this context as a particular case within a larger ensemble of physical phenomena, this approach does not provide general principles from which natural selection can be derived. Turning back to evolutionary biology, we ask to what extent the most general formulations of the necessary conditions or signatures of natural selection may be applicable beyond biology. In our view, such a cross-disciplinary jump is impeded by reliance on individuality as a central yet implicit and loosely defined concept. Overall, these discussions thus lead us to conjecture that understanding, in physico-chemical terms, how individuality emerges and how it can be recognised, will be essential in the search for instances of evolution by natural selection outside of living systems. (shrink)

The endocellular bacteriumWolbachiamanipulates the reproduction of its arthropod hosts for its own benefit by various means, the most widespread being cytoplasmic incompatibility (CI). To date, the molecular mechanism involved in CI has not been elucidated. We examine here three different CI models described in previous literature, namely, the “lock‐and‐key”, “titration–restitution” and “slow‐motion” models. We confront them with the full range of CI patterns discovered so far, including the most complex ones such as multiple infections, asymmetrical and partial compatibility relationships and (...) the existence ofWolbachiavariants that can rescue the host from CI but not induce it. We conclude that the lock‐and‐key model is the most parsimonious of the models and fits the observations best. The two other models cannot be categorically invalidated, but they encounter some difficulties that make additional hypotheses necessary. BioEssays 25:259–265, 2003. © 2003 Wiley Periodicals, Inc. (shrink)