Define homeostasis.

Homeostasis refers to the ability of an organism to maintain a stable internal environment despite fluctuations in external conditions. This concept is vital for the survival of organisms, as it ensures that internal factors such as temperature, pH, and concentrations of various ions and nutrients remain within appropriate ranges. For example, human bodies regulate temperature through processes like sweating and shivering, which help to keep the body's temperature within a functional range regardless of changes in the external environment. This stability allows organisms to function optimally and respond to environmental stresses, contributing to overall health and resilience.

The other choices pertain to different biological concepts. The process of evolution describes gradual changes in populations over time, while the rate at which an organism consumes energy relates to metabolic processes. Genetic variation refers to the diversity of genetic traits within a population, which plays a role in evolution and adaptation but is not directly related to the concept of maintaining internal stability.