One of the features that nearly every mammal species on Earth (including humans) have in common is that their bodies are covered in structures known individually as "hairs" and collectively as "fur."

To learn more about animals' appearance, Bored Panda reached out to Dr. Hopi E. Hoekstra, who is the Alexander Agassiz Professor of Zoology in the Departments of Organismic & Evolutionary Biology and Molecular & Cellular Biology at Harvard University, the Curator of Mammals at the Museum of Comparative Zoology, and a Howard Hughes Medical Institute Investigator.

"Fur on a mammal looks different (or the same) based on (1) hair length, (2) its thickness, and (3) its density as well as (4) its composition, that is, the composition of different hair types," she explained. "For example, most rodents have 4 hair types: awl, zig-zag, auchene, and guard hairs."

"Guard hairs, for instance, tend to be coarse, thick, and long but found only on certain regions of the body (eg. the rump or back of the neck); relative to other hair types, guard hairs are not very numerous. Some hair morphology is extreme: spines are modified hairs that have evolved repeatedly within rodents. Of course, hair pigmentation is an obvious trait that may make animals look more or less similar."

We also reached out to Dr. Jessica E. Light, the Associate Professor and Curator of Mammals at Texas A&M University. She said that there are 4 main purposes of fur:

1) insulation;

2) tactile or sensory (think whiskers, which are a type of hair);

3) protection (guarding the skin and shielding against predators (think quills and spines));

4) visual (colors of fur provide information to members of the same species and other species).

Dr. Hoekstra added that "some species, like sea otters, have incredibly dense fur that both keeps them warm in cool ocean water but also helps with buoyancy."

"Polar bears have unique hairs that are effectively hollow and can 'capture' heat from the sun to keep them warm. Some hairs have piloerection, in which hairs can be lifted upwards as a threat display. The pigments in hairs also play an important function, primarily in camouflage."

Some animal coats are more distinctive than others. But that doesn't mean they're easier to understand. It has long been suggested that arguably the most eccentric mammal, the zebra, may have developed its unique striping to hide from lions and deter biting tsetse flies.

But according to one comprehensive study, the iconic stripes along a zebra's back are most closely correlated with temperature and precipitation in its environment, not the prevalence of lions or tsetse flies. These findings could mean that the famous black-and-white coat actually helps the zebra to regulate its body temperature.

Since animals' fur can make the difference between life and death, they try to keep it in tip-top condition. "Grooming, especially of hair, can be very important for mammals," Dr. Hoekstra said. The main purpose is to remove potential parasites/pathogens (not necessarily to "look good"). When an animal is ill or old, they tend to groom less and thus may look more disheveled. It is unclear if this is used as a 'signal' to other individuals."

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