Abstract
AbstractThe analysis of network topology and dynamics is increasingly used for the description of the structure, function and evolution of complex systems. Here we summarize key aspects of the evolvability and robustness of the hierarchical network-set of macromolecules, cells, organisms, and ecosystems. Listing the costs and benefits of cooperation as a necessary behaviour to build this network hierarchy, we outline the major hypothesis of the paper: the emergence of hierarchical complexity needs cooperation leading to the ageing of the constituent networks. Local cooperation in a stable environment may lead to over-optimization developing an ‘always-old’ network, which ages slowly, and dies in an apoptosis-like process. Global cooperation by exploring a rapidly changing environment may cause an occasional over-perturbation exhausting system-resources, causing rapid degradation, ageing and death of an otherwise ‘forever-young’ network in a necrosis-like process. Giving a number of examples we explain how local and global cooperation can both evoke and help successful ageing. Finally, we show how various forms of cooperation and consequent ageing emerge as key elements in all major steps of evolution from the formation of protocells to the establishment of the globalized, modern human society. Thus, ageing emerges as a price of complexity, which is going hand-in-hand with cooperation enhancing each other in a successful community.
Highlights
Evolvability, robustness and ageing of hierarchical networks The network approach proved to be a highly efficient cognitive tool to describe various levels of the hierarchical organization of complex systems from macromolecular structures to the currently emerging world-wide social networks
Networks display a lot of rather general properties, such as (a) small-worldness, meaning the existence of short pathways between most network elements; (b) the existence of hubs, which have a much higher number of neighbours than the average of network elements; (c) modular structure, which organizes networks to various overlapping groups; (d) the co-existence of strong and weak links, where the link-strength is usually defined as the real, physical strength of the connection, or as the probability of interactions and (e) the existence of a network skeleton, which is the subset of most important pathways in the network
Non-cooperating, creative elements may preserve the ‘forever young’ phenotype even in the middle of an ‘always-old’ network.[40]. Creative entrepreneurs in the age of 50 preserve a risk-taking behaviour typical to the age of 25, which gives a good example of the slow ageing of these non-cooperators.[70]. Recent data suggest that the senescence of creative elements, such as stem cells, is an especially important step in the ageing process of the whole complex system.[19]. The emerging diversity of either differently over-optimized or differently damaged networks may trigger their cooperation
Summary
Listing the costs and benefits of cooperation as a necessary behaviour to build this network hierarchy, we outline the major hypothesis of the paper: the emergence of hierarchical complexity needs cooperation leading to the ageing of the constituent networks. Local cooperation in a stable environment may lead to over-optimization developing an ‘always-old’ network, which ages slowly, and dies in an apoptosis-like process. Global cooperation by exploring a rapidly changing environment may cause an occasional over-perturbation exhausting system-resources, causing rapid degradation, ageing and death of an otherwise ‘forever-young’ network in a necrosis-like process. We show how various forms of cooperation and consequent ageing emerge as key elements in all major steps of evolution from the formation of protocells to the establishment of the globalized, modern human society. Ageing emerges as a price of complexity, which is going hand-in-hand with cooperation enhancing each other in a successful community
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