Biological differences between endotherms and ectotherms

The biological distinction between warm-blooded and cold-blooded animals relies on how they regulate body temperature. Evolutionary biologist Manuel Leal from the University of Missouri explains that warm-blooded organisms are endotherms, meaning they generate internal heat to maintain a constant body temperature, such as the human standard of 37 degrees Celsius.

In contrast, cold-blooded animals are ectotherms, meaning their body temperature is dependent on the external environment. While terms like ‘cold-blooded’ are common, they can be misleading; for example, a reptile basking in the sun can become warmer than a mammal.

The linguistic origins of these terms trace back to the Theory of Humors established by ancient Greek physicians like Hippocrates and Galen. This medical theory, which dominated science until the 17th century, suggested that bodily fluids controlled character and that emotions could literally cause blood to heat up.