Stochasticity, individuality and behavior

No two individuals are exactly alike. More than a simple platitude, this observation reflects the fundamentally stochastic nature of biological systems. The term 'stochastic' describes features that cannot be predicted a priori from readily measurable variables. In the dichotomous framework in which biological variation arises from genetic or environmental effects, stochastic effects are classified as environmental because they are not passed on to offspring - any non-heritable cause is, by definition, environmental. But non-heritable effects can be subdivided into those which can be predicted from measurable variables, and those that cannot. These latter effects are stochastic.