COMPLEXITY, CHAOS AND BIOLOGICAL EVOLUTION
by Professor E. Mosekilde, Technical University of Denmark, Lyngby (Denmark)
The discovery of deterministic chaos and the development of nonlinear science have changed many of our basic concepts in physics. Recognition of the fractal nature of the underlying geometrical structure and the existence of universal quantitative relations for the development of deterministic chaos has generated new excitement within a broad spectrum of different disciplines ranging from celestial mechanics, differential topology and global analysis, over statistical mechanics and ergodicity theory to quantum mechanics and nuclear physics (ASI SERIES B208, B268, and C358).
One of the most obvious areas in which to apply and further develop this insight is biology. Many cells exhibit pulsatory variations in their membrane potential with complicated patterns of slow and fast spikes. Heart cells, for instance, have been found to produce chaos and various forms of mode-locking when stimulated externally. Similarly, the interaction between nerve cells can give rise to nonlinear dynamic phenomena with frequency locking and chaotic firing influencing the flow of information. Rhythmic signals also seem essential in intercellular communication. Besides neurons and muscle cells which communicate by trains of electrical pulses, examples range from the generation of cyclic AMP pulses in the slime mold Dictyostelium discoideum to the pulsative release of hormones. While in these instances the oscillatory dynamics characterize the extracellular signal, recent observations indicate that signal transduction within the cell involve oscillations or spiral waves of intracellular messengers. These and related observations in a variety of other systems pose fundamental questions concerning the functioning of biological control systems.
A particularly interesting topic is the evolution of biological forms (ASI SERIES B225, B260, and B263). The fact that it is possible to classify species morphologically into hierarchical taxonomies reveals a logical order within the biological realm as a whole. It is likely that this stems from the hierarchical dynamic organization of morphogeneses itself. The research program to which this leads is an experimental and theoretical study of developing organisms with the goal of identifying the generic properties which result in robust, but highly modifiable patterns of morphogenesis.
At the same time, the emergence of life out of simple organic and inorganic compounds remains one of the most fascinating scientific problems, to the solution of which the theory of complex systems offers new approaches. One such approach, which has come to be known as Artificial Life, attempts to create life-like behavior and intrinsic evolutionary dynamics by means of computer programs. One is concerned with finding ways of formulating evolutionary dynamics as open-ended problems, i.e., as problems where the various roads that evolution may take have not already been laid down by the modeler.
The present volume (NATO ASI SERIES B270) comprises a series of 30 papers presenting the most recent theoretical and experimental results within a variety of different fields including hormonal regulation, cell-to-cell signalling, bone remodelling and much more.
Reference books: B208, B225, B260, B262, B263, B268, B270, C358