  A common trait of complex systems is that they can be represented by means of
a network of interacting parts. It is, in fact, the network organisation (more
than the parts) what largely conditions most higher-level properties, which are
not reducible to the properties of the individual parts. Can the topological
organisation of these webs provide some insight into their evolutionary
origins? Both biological and artificial networks share some common
architectural traits. They are often heterogeneous and sparse, and most exhibit
the small-world property or the presence of modular or hierarchical patterns.
These properties have often been attributed to the selection of functionally
meaningful traits. However, the proper formulation of generative network models
suggests a rather different picture. Against the standard
selection-optimisation argument, some networks reveal the inevitable generation
of complex patterns resulting from reuse and can be modelled using
duplication-rewiring rules. These give rise to the heterogeneous, scale-free
and modular architectures observed in the real case studies. Tinkering is a
universal mechanism that drives not only biological evolution but also the
large-scale dynamics of some technological designs. Here we examine the
evidence for tinkering in cellular, technological and ecological webs and its
impact in shaping their architecture and deeply affecting their functional
properties. Our analysis suggests to seriously reconsider the role played by
selection forces or design principles as main drivers of network evolution.

Populations and Evolution;Molecular Networks