Individual variation in endocrine systems: moving beyond the ‘tyranny of the Golden Mean’

摘要

Twenty years ago, Albert Bennett published a paper in the influential book New directions in ecologicalrnphysiology arguing that individual variation was an ‘underutilized resource’. In this paper, I review ourrnstate of knowledge of the magnitude, mechanisms and functional significance of phenotypic variation,rnplasticity and flexibility in endocrine systems, and argue for a renewed focus on inter-individualrnvariability. This will provide challenges to conventional wisdom in endocrinology itself, e.g. re-evaluationrnof relatively simple, but unresolved questions such as structure–function relationships amongrnhormones, binding globulins and receptors, and the functional significance of absolute versus relativernhormone titres. However, there are also abundant opportunities for endocrinologists to contribute solidrnmechanistic understanding to key questions in evolutionary biology, e.g. how endocrine regulation isrninvolved in evolution of complex suites of traits, or how hormone pleiotropy regulates trade-offs amongrnlife-history traits. This will require endocrinologists to embrace the raw material of adaptationrn(heritable, individual variation and phenotypic plasticity) and to take advantage of conceptualrnapproaches widely used in evolutionary biology (selection studies, reaction norms, concepts ofrnevolutionary design) as well as a more explicit focus on the endocrine basis of life-history traits that arernof primary interest to evolutionary biologists (cf. behavioural endocrinology).