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Scale invariance in biology: coincidence or footprint of a universal mechanism?
Article first published online: 31 JAN 2007
Volume 76, Issue 2, pages 161–209, May 2001
How to Cite
GISIGER, T. (2001), Scale invariance in biology: coincidence or footprint of a universal mechanism?. Biological Reviews, 76: 161–209. doi: 10.1017/S1464793101005607
- Issue published online: 31 JAN 2007
- Article first published online: 31 JAN 2007
- (Received 4 October 1999; revised 14 July 2000; accepted 24 July 2000)
- Scale invariance;
- complex systems;
In this article, we present a self-contained review of recent work on complex biological systems which exhibit no characteristic scale. This property can manifest itself with fractals (spatial scale invariance), flicker noise or 1/f-noise where f denotes the frequency of a signal (temporal scale invariance) and power laws (scale invariance in the size and duration of events in the dynamics of the system). A hypothesis recently put forward to explain these scale-free phenomomena is criticality, a notion introduced by physicists while studying phase transitions in materials, where systems spontaneously arrange themselves in an unstable manner similar, for instance, to a row of dominoes. Here, we review in a critical manner work which investigates to what extent this idea can be generalized to biology. More precisely, we start with a brief introduction to the concepts of absence of characteristic scale (power-law distributions, fractals and 1/f-noise) and of critical phenomena. We then review typical mathematical models exhibiting such properties: edge of chaos, cellular automata and self-organized critical models. These notions are then brought together to see to what extent they can account for the scale invariance observed in ecology, evolution of species, type III epidemics and some aspects of the central nervous system. This article also discusses how the notion of scale invariance can give important insights into the workings of biological systems.