Final answer:
Animals maintain a stable internal environment through homeostasis, which involves regulating internal conditions to adapt to external environmental changes. They use various structures and feedback mechanisms to achieve thermoregulation.
Step-by-step explanation:
Animals maintain an overall steady state of internal conditions through a process known as homeostasis. This process allows them to regulate internal conditions within a narrow range almost constantly, despite changes in the external environment. For example, the regulation of body temperature, or thermoregulation, is necessary for organisms to survive in both cold and hot climates. Structures like fur, feathers, blubber, and fat help in insulation, while methods such as perspiration in humans or panting in dogs help to release excess body heat. Additionally, feedback mechanisms are crucial for maintaining internal conditions and responding to external environmental changes.