What is an example of a physiological adaptation to extreme cold?

Thicker fur or fat layers serve as an effective physiological adaptation to extreme cold because they help animals maintain their body temperature in frigid environments. Fur acts as an insulator, trapping air close to the skin and reducing heat loss, while fat provides both insulation and energy reserves. In cold climates, mammals often develop thicker fur or increased fat layers to combat the heat loss that occurs due to lower ambient temperatures. This adaptation is crucial for survival, as it allows animals to conserve body heat and maintain thermal regulation despite the harsh conditions.

The other options, while they can be related to the overall response to cold environments, do not directly represent physiological adaptations that specifically counteract extreme cold in the same manner as insulating layers do. For example, a reduced heart rate might occur in some scenarios, but it does not enhance the ability to survive or thrive in cold temperatures like increased insulation does. Increased metabolic rate may help generate more heat but can also lead to faster depletion of energy reserves, which is not sustainable over time without adequate food intake. Changing feeding habits could provide various benefits, yet it does not specifically address the mechanisms of heat retention compared to physical adaptations like thicker fur or fat layers.