Biological Insulation

As people, we need insulation in relatively extreme environments to maintain comfortable living conditions and maintain bodily functions. However, we use brains to build shelters that will maintain these conditions for us. How do animals that live in extreme conditions maintain adequate body temperatures?

This discussion will only focus on insulating adaptations in extreme cold weather environments, as in extreme hot weather environments, insulation is much less common and maintaining body temperature mostly focuses on increasing heat loss.

A simple way that animals can control their body temperature is through their size and metabolism. Larger animals have a larger volume-to-surface area ratio, so they have a larger amount of body mass producing heat that is dissipated away in a relatively small surface area. Marine and semi-aquatic mammals are all relatively large compared to their terrestrial counterparts in large part because a larger volume to surface area ratio leads to relatively less heat loss. An aquatic mammal that is too small would have to spend too much energy just to maintain their body heat. As another example, polar bears do not have hair adapted for containing air while underwater, although it is good for shedding water on land. Because their hair isn't a great insulator while swimming, polar bears rely on their large volume to surface area ratio, increasing their metabolism, and constricting their blood flow to their skin to avoid heat loss while they are swimming. Many small mammals like mice will rely almost exclusively on their high metabolism to stay warm in cold environments because an insulative coat would be to heavy and cost too much energy.

As stated on previous pages, air is a very good insulator. Because the insulating properties of air are very easy to take advantage of, many mammals in extreme environments will trap air with their fur for insulation. Many animals have fur that comes in two types, a guard hair and a underfur. The guard hairs are responsible for keeping water away from the skin and underfur, preventing wind penetration and abrasion, giving the animal its color, and are coarser than the underfur. The underfur is responsible for insulation, and is much finer and denser than the guard hairs. Hair shape, texture, and size will determine the properties of the fur. Some animals, like deer, moose, and polar bears, will have hollow guard hairs to help trap air and increase their insulation. However, most animals will just rely on their underfur for insulation, and guard hairs for protection.

Another biological insulator is blubber. Blubber is found in many marine mammals such as whales, seals, and manatees. It is composed of a dense fat layer beneath the skin of these animals. Why would these animals rely on blubber for insulation instead of fur like many other animals? Even other marine mammals, like sea otters, utilize fur for insulation instead of blubber. Fur works by trapping air in it, which creates a layer of low conductivity between the animal's body and the environment. Unless a marine mammal's fur is specially adapted for an aquatic environment, it the water will just replace the air in the fur and significantly increase the body's heat loss. However, blubber isn't affected by water pressure and has other benefits besides insulation, so many marine mammals have evolved to have blubber instead of fur.

The odd animal out from these is the sea otter. The sea otter is a fully aquatic animal, but it relies almost solely on fur for its insulation. They don't have massive stores of blubber like other marine mammals do. Instead, they have extremely dense hair of up to 1 million hairs per square inch to trap air in their fur. Sea otters will also spend a significant amount of time foraging for food to maintain a high metabolisms. When they are not foraging, sea otters will often be grooming their hair to clean it of debris and chemicals, and to help trap air inside of it. Their fur works well for insulation, but it does mean that they spend much of their energy maintaining it to stay warm.

Although the insulation strategies between different animals is interesting, the similarities between them is also a cool instance of convergent evolution. Whales and seals aren't closely related, but they both rely on blubber and their relatively large size for insulation. These similar traits are fascinating and show how the physics of a problem will lead to similar solutions.


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