Figure 24.1 An arctic fox is a complex animal, well adapted to its environment. It changes coat color with the seasons, and has longer fur in winter to trap heat. (credit: modification of work by Keith Morehouse, USFWS)

The structures of animals consist of primary tissues that make up more complex organs and organ systems. Homeostasis allows an animal to maintain a balance between its internal and external environments.

The arctic fox is an example of a complex animal that is well adapted to its environment and illustrates the relationships between an animal’s form and function. According to researchers, animals living millions of years ago in the Himalayan Mountains of Tibet are ancestors to many of today’s cold-adapted animals. For example, a type of Tibetan fox from three to five million years ago is the ancestor to the arctic fox. More about this research can be found at the Science Daily website.