Observation of living systems on many levels, as well as of processes leading to planet formation and the biogeochemical cycles needed to support life, suggest that the establishment of subsystem-correlations may proceed inward and/or outward from a relatively-small number of very different emergent boundary types[6]. In the outward-looking case, development of subsystem-correlations often naturally starts with subsystem-subsystem i.e. pair interactions. Preliminary observations on single-level ordering in rather complex systems like neural nets\cite{Schneidman2006} also suggest that outward-focused ordering processes center primarily around subsystem pair correlations.
Boundary-emergence itself, and the post-pair or inward ordering processes subsequent thereto, are often treated as a separate subject. Traditional applications of long-standing interest here include e.g. studies of planetary accretion, homogeneous nucleation, and alliance-formation in context of the game-theory prisoner's dilemma\cite{Nowak2006}.
The presence of inward-looking subsystem-correlations is perhaps easiest to see once a higher-level of organization is in place. Thus for example mechanisms to preserve the integrity of a cell-membrane for controlled molecule-exchange with the outside world are likely in place partly to ensure microbe-viability, even though they manifest as multi-molecule correlations on the molecular level. Exploration of the precise mechanisms by which subsystem correlations at one level interact with subsystem correlations at the next level up is still in its early days, but of course is quite relevant e.g. to the topic of gene-pool/idea-pool co-evolution\cite{Richerson2004} so relevant in today's electronic-information age.
Thus hierarchical ordering in the layer just above a pair-correlated level (e.g. interacting organisms) may generally require a higher-level symmetry-break (e.g. recognition of differing organism groups), which in turn gives rise to processes that select for inward-looking (e.g. from the group boundary) post-pair correlations as well as outward-looking pair-correlations on the next level up (e.g. between groups).
Thus shared-electrons break the symmetry between in-molecule and extra-molecule interactions, bi-layer membranes allow symmetry between in-cell and out-cell chemistry to be broken, shared resources (like steady-state flows) may break the symmetry between in-tissue and external processes, metazoan skins allow symmetry between in-organism and out-organism processes to be broken, bias toward family breaks the symmetry between in-family and extra-familial processes, membership-rules break the symmetry between in-culture and multi-cultural processes, etc.
In this paper we focus on the perspective of (a) metazoan individuals as both audience and agent, instead of for instance on (b) the perspective of individual micro-organisms, or (c) the perspective of whole family gene-pools even though this is of much recent interest in biology. In that context, therefore, we center our attention on the last three symmetry-break levels (skin, family, culture) and the six subsystem-correlation layers (inward and outward from each boundary) associated therewith.
Related references:
Elad Schneidman, Michael J. Berry, Ronen Segev and William Bialek (2006) "Weak pairwise correlations imply strongly correlated network states in a neural population", Nature 440:7087, 1007-1012.
Martin A. Nowak (2006) Evolutionary Dynamics: Exploring the Equations of Life (Belknap Press, Harvard U.) preview.
Peter J. Richerson and Robert Boyd (2004) Not by genes alone (U. Chicago Press, IL).