Among the unresolved topics in evolutionary biology and behavioral ecology are the origins, mechanisms, evolution, and consequences of developmental and phenotypic diversity. In an attempt to address these challenges, plasticity has been investigated empirically and theoretically at all levels of biological organization--from biochemical to whole organism and beyond to the population, community, and ecosystem levels. Less commonly explored are constraints (e.g., ecological), costs (e.g., increased response error), perturbations (e.g., alterations in selection intensity), and stressors (e.g., resource limitation) influencing not only selective values of heritable phenotypic components but, also, decisions and choices (not necessarily conscious ones) available to individuals in populations. Treating extant mammals, the primary purpose of the proposed work is to provide new perspectives on common themes in the literature on robustness ("functional diversity"; differential resistance to "deconstraint" of conserved elements) and weak robustness (the potential to restrict plasticity and evolvability), plasticity (variation expressed throughout the lifetimes of individuals in a population setting "evolvability potential"), and evolvability (non-lethal phenotypic novelties induced by endogenous and/or exogenous stimuli). The proposed project will place particular emphasis upon the adaptive complex in relation to endogenous (e.g., genomes, neurophysiology) and exogenous (abiotic and biotic, including social environments) organismal features discussed as regulatory and environmental perturbations with the potential to induce, and, often, constrain variability and novelty of form and function