Introduction

An adaptive response is an inevitable consequence of sustained perturbation in the environment and may be genetic, physiological and or behavioural. They are not completely separate entities as they interact with each other at several levels and are not without cost to the organism. Every adaptation has its cost and there is no such thing as a ‘ costless ’ adaptation. The processes and the costs involved may be: overt or covert, reversible or irreversible and transient or permanent. An adaptive response is a homeostatic response. However, the term ‘ homeostasis ’ pertains to maintenance of the constancy of the internal milieu when changes occur within the acceptable range of physiological variability. A sustained perturbation in any one direction will result in responses which will further the survival of the individual and help maintain homeostasis but at a cost to the organism. A homeostatic response may neither have additional costs to the organisms nor lead to compromise in its function, capability, or performance, while an adaptive response may do both in order to further the survival of the individual. Adaptation is a relatively slow process and should be distinguished from the rapid regulatory role of homeostatic mechanisms.

Adaptations in energy metabolism of humans

It has been suggested that the energy metabolism of individuals is more variable and adaptable than previously believed, and that allowances need to be made for this when arriving at estimates of human energy requirements.