  What features characterise complex system dynamics? Power laws and scale
invariance of fluctuations are often taken as the hallmarks of complexity,
drawing on analogies with equilibrium critical phenomena[1-3]. Here we argue
that slow, directed dynamics, during which the system's properties change
significantly, is fundamental. The underlying dynamics is related to a slow,
decelerating but spasmodic release of an intrinsic strain or tension. Time
series of a number of appropriate observables can be analysed to confirm this
effect. The strain arises from local frustration. As the strain is released
through "quakes", some system variable undergoes record statistics with
accompanying log-Poisson statistics for the quake event times[4]. We
demonstrate these phenomena via two very different systems: a model of magnetic
relaxation in type II superconductors and the Tangled Nature model of
evolutionary ecology, and show how quantitative indications of ageing can be
found.
