What type of hair primarily serves a protective function on animal bodies?

The correct answer is guard hair, which primarily serves a protective function on animal bodies. Guard hairs are the longer, coarser hairs that form the outer layer of fur or hair coats in many mammals. They provide several critical roles, including protecting the underlying layers of hair and skin from environmental elements such as moisture, UV radiation, and debris.

In addition to their protective properties, guard hairs often play a role in thermoregulation by allowing for the shedding of rain and preventing water from reaching the insulating undercoat. Furthermore, they can assist with camouflage, helping animals blend into their surroundings, which offers an additional layer of protection from predators.

Other types of hair, like whiskers or tactile hair, are specialized for sensing the environment rather than providing protection. The undercoat, while important for insulation, does not serve the same protective role that guard hairs do. Thus, guard hair is essential for maintaining the health and integrity of an animal's body in various environments.