Humans are obsessed with staying clean. We bathe or shower regularly (at least most of us do). We trim our hair and nails. Some people even pay for other people to groom them when it comes to pedicures or facials.

Hygiene isn’t just a modern fad. It’s an instinct that humans evolved for well before bathtubs, loofahs, and shampoo. Archaeological evidence suggests humans began combing, plucking, and cutting their hair at least 3,000 years ago.

While bathing and grooming is an innate part of being human, there is also evidence that animals, even the ones not so closely related to us, maintain hygiene in some way.

The evolutionary advantages of bathing and grooming might seem clear — to remove potentially harmful bacteria from the body. But hygiene practices serve many purposes that differ animal to animal.

1. Grooming Habit in Himalayan Tahrs: Reciprocity

Himalayan tahrs are goat-like horned ungulates that are adapted to the high-alpine tundra of the Himalayan range. Like many ungulates, they groom each other’s fur by scraping and licking with their teeth and tongues.

Recently, a group of scientists paid close attention to these behaviors amongst a cohort of unrelated female tahrs at an open-air zoo in Rome. They were looking to poke holes in the cognitive constraint hypothesis, which claims that non-human animals do not have the cognitive ability to understand reciprocity in the long term. Therefore, mutually beneficial behavior has to give an immediate benefit to both parties. In other words, if you scratch my back, I’ll scratch yours right now.

As the scientists suspected, the Himalayan tahrs didn’t fit the mold. They showed a preference to groom individuals that had groomed them previously, even if hours or days had passed.

The authors argued that their observations provided counter evidence to the cognitive constraint hypothesis. Yet, the tahrs’ behavior could also lead to a third explanation. It could be that the animals developed affinity for each other through grooming. Perhaps it’s not calculated reciprocity — just friendship.

Read More: 20 of the Most Adorable Animals To Help Make Anyone’s Day

2. African Lion Grooming: Social Bonding

Tahrs aren’t the only animals that enjoy grooming each other. Social grooming, or allogrooming, has been observed in many mammals, birds, and even insects.

For many animals, social grooming is reserved for close kin. But some, like tahrs, seem to receive some other benefit from the behavior.

African lions lick each other’s fur and rub heads with members of their pride. Though they tend to favor close relatives, they also preferentially groom unrelated lions that are close in age.

The evolutionary purpose of this behavior is still somewhat opaque. But observations increasingly suggest that grooming provides social benefits to lions. It’s a way to affirm friendships and show affection. After all, relationships are important when you live and hunt in a pride.

3. Grooming for Beavers: Waterproofing Fur and Feathers

Some animals’ hygiene practices serve a more practical purpose. Many aquatic animals habitually groom and oil-up their fur or feathers to keep dry.

Beavers groom themselves multiple times a day. In fact, they have evolved highly specialized tools for the task. On each hind leg, they have a split claw — a serrated bony growth that they use to meticulously comb their fur. They also have specialized glands near their anus that secrete an oily substance, which they spread over their fur during the grooming process. The oil keeps them warm and dry during long days in the water.

Many aquatic birds have a similar gland, commonly known as the preen gland. Ducks, for instance, scoop up the oily secretion from the preen gland and spread it over their feathers to waterproof them.

4. Bush Elephant Bathing: Staying Cool in the Heat

It gets hot on the African Savannah, especially when you’re a 6-ton mammal that can’t fully fit under a tree for shade.

African bush elephants have found another use for bathing — staying cool. On hot days, they coat themselves in mud to stay wetter longer. One group of scientists found that elephants were more likely to get themselves wet and muddy on days when the temperature rose above 91 degrees Fahrenheit in the sun.

Researchers have also found that Asian elephants coat themselves in dirt and dust when it’s hot out. Interestingly, their observations led them to believe that the purpose of the dust baths was not temperature regulation. Instead, the behavior might help prevent sunburn or ward off parasites.

Read More: 6 Different Tactics That Animals Use to Prepare for Winter

5. Honeybee Grooming: Shedding Pests

Perhaps one of the best-understood purposes of hygiene is to rid the body of unwanted guests. Animals of all shapes, sizes, and evolutionary lineages engage in behaviors that ward off parasites, viruses, and harmful bacteria. Think of a dog biting off fleas or a horse swatting flies with its tail.

For eusocial insects, like honeybees, grooming for parasites can be a collective activity rather than an individual one. European honeybees regularly comb through the hairy area under their nest mates wings using their mandibles. It’s an impossible-to-reach spot yourself, and, accordingly, it’s where parasitic mites like to hide. By grooming each other, the bees are ensuring the health of the hive as a whole.

Article Sources

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Gabe Allen is a Colorado-based freelance journalist focused on science and the environment. He is a 2023 reporting fellow with the Pulitzer Center and a current master’s student at the University of Colorado Center for Environmental Journalism. His byline has appeared in Discover Magazine, Astronomy Magazine, Planet Forward, The Colorado Sun, Wyofile and the Jackson Hole News&Guide.