Human system variation and selection

There are five sources of variation in the human system: 1) genetic, 2) epigenetic, 3) phenotypic, 4) cultural, and 5) path dependent individual variation. These five sources of variation are manifested in an individual as they interact with a dynamic, heterogenous and varyingly uncertain/unpredictable exogenous environment. The outcome, then, is determined by a less-than-clear combination of some minimum of 15 combinations of variables (more when allowing for unique combinations arising from internal variation, interaction and feedback loops). Hence the difficulty of nailing down simplistic, universally explanatory root causes when it comes to the human system.