What does endothermy mean?
Endothermy is the biological condition in which an animal generates and regulates its own body heat through internal metabolism rather than depending on external sources such as sunlight. Endothermic animals — commonly known as warm-blooded animals — include all birds and mammals, along with a few exceptional species such as tunas and some sharks that warm only certain tissues. This capacity allows them to remain active in cold environments and at night, sustaining steady activity levels regardless of ambient conditions. The trade-off is cost: endothermy demands substantial energy, which is why these animals generally require more food than their ectothermic counterparts. In scientific writing, 'endothermy' appears frequently in discussions of evolution, metabolism, and ecology, particularly in debates over when and why warm-bloodedness first arose. It contrasts directly with ectothermy, the strategy of fishes, reptiles, amphibians, and most invertebrates. Though technical in register, it is a precise and valuable word for anyone writing about animal biology.
nounThe physiological condition of maintaining a relatively constant internal body temperature through internally generated metabolic heat, independent of the external environment. It is characteristic of birds and mammals, among other animals.
- The physiological trait of generating and regulating internal body heat metabolically so that body temperature remains largely stable regardless of ambient conditions (biology/zoology).
"Endothermy allows penguins to remain active in Antarctic waters where most reptiles would quickly succumb to the cold."
"The evolution of endothermy is often cited as a key factor in the success of mammals and birds across diverse habitats."
"Certain large fish, such as tuna and some sharks, exhibit regional endothermy, warming only specific organs or muscles."
The plural is rare and appears only when discussing multiple instances or types of the phenomenon, e.g. across different species or evolutionary origins.
"Regional and full-body endothermies have evolved independently in several fish lineages."
You are walking proof of endothermy: your body burns energy around the clock just to keep itself at roughly 37°C, no matter the weather.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of endothermy
Endothermy derives from Greek roots: 'endo-', meaning 'within', and 'thermē', meaning 'heat', joined by the noun-forming suffix '-y' that marks a state or condition. The term was coined within nineteenth-century physiological science as biologists sought precise vocabulary to distinguish animals that produce their own heat from those dependent on external warmth. Its relatives include 'endothermic' (absorbing heat), 'ectothermy', and the broader family of thermal terms such as 'hypothermia' and 'thermometer', all built on the same Greek root.
Related word forms
How endothermy is actually used
A technical term used chiefly in zoology, physiology, and evolutionary biology; it is uncommon in everyday speech. Animals exhibiting endothermy are called endotherms, though they are popularly described as 'warm-blooded'. Note that endothermy does not always imply a constant body temperature — some endotherms allow their temperature to vary (heterothermy), and some ectotherms maintain fairly stable temperatures behaviourally.
Easily confused with endothermy
Endothermy is generating body heat internally through metabolism, whereas ectothermy is relying on external sources like sunlight or warm surfaces for body heat.
'Endothermy' is the noun describing warm-blooded physiology in animals, while 'endothermic' is an adjective used mainly in chemistry for reactions that absorb heat.