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8th grader's award-winning experiment tested if dogs' tongues are really cleaner than ours

Here's what science says about letting your dog lick your face.

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Should you let a dog lick your face?

With nearly half of the households in American having at least one dog, there's a lot people need to know about them. Our furry friends come in wide variety of breeds, each with their own unique traits and needs. "Man's best friend" can be a guardian, a helpful worker, a loyal friend, and a snuggly companion, but there's one thing almost all dogs have in common: Licking.

Some dogs lick way more than others, but it's rare to find a dog who never licks anyone or anything. Many dogs communicate and show affection by licking, which is sweet—if a little gross—depending on how slobbery they are. There's a common saying that dogs' mouths are cleaner than humans', which is a bit hard to believe when you see what some dogs put in their mouths, but it is true? What does science say about dog tongues and saliva? Is a dog licking our face something we should worry about?

 dogs, dog mouths clean, dog tongues, dog licking, should you let a dog lick your face Pooch smooches are sweet if they're not too slobbery.Photo credit: Canva

It turns out, the answer to whether a dog's mouth is cleaner than ours isn't super straightforward.

An 8th grader named Abby tackled this question in a science experiment that won her a Young Naturalists Award from the American Museum of Natural History in 2011. Her family had gotten a dog and her mom kept telling her not to let the dog lick her face because dog mouths are full of bacteria. Instead of arguing, Abby decided to find out herself if this was true.

"I hypothesized that human tongues would be cleaner than dog tongues," she wrote. "I thought this because humans brush their teeth at least once a day. I hypothesized that dogs' tongues would be dirty because they were always licking dirty things like garbage."

After diving into the research about bacteria that live in and on humans and dogs, Abby decided she had a testable hypothesis. But this wasn't any old middle school science experiment. She applied for and got a grant to the State Hygienic Lab at the University of Iowa, where she was assigned a mentor to work with her.

You can read the nitty gritty details of her experiment here, but here was her conclusion:

 dogs, dog mouths clean, dog tongues, dog licking, should you let a dog lick your face Many dogs will lick you if you give them the chance. Photo credit: Canva

"I concluded that dog and human mouth flora are very different. (Flora means the bacteria found in a mouth or anywhere else.) The bacteria found in human mouths are more similar to another human's oral bacteria than the bacteria found in a dog's mouth.

I also concluded that dogs' mouths are cleaner than humans' in some ways, and dirtier in other ways. Humans have more bacteria in their mouths than dogs do, based on the total number of bacteria. Most of the humans had a 'moderate' number of bacteria, and most of the dogs had 'few' bacteria. A possible explanation of this might be that dogs pant a lot, and maybe while panting, bacteria falls off their tongues along with their saliva. But dogs had more types of bacteria. The average number of different bacterial colonies in a dog's mouth was about 5.7. The average number of different bacterial colonies in a human's mouth was about 4.1. I think this is so because dogs sniff and lick a variety of things, like carpets, floors, chairs, grass, etc., so they pick up bacteria from many places."

But what about the licking of our faces? That's a bit of a subjective call, but Abby's results gave her some peace of mind:

"In conclusion, will I let my dog continue to lick me? The answer to the question is yes!" she wrote. "I will feel guiltless about letting my dog lick me because I found out that human and dog oral bacteria are different, so my dog's oral bacteria present no harm to me."

 lick, licking, face, dogs, dog puppy love kiss GIF by Pickler & Ben  Giphy  

What do the experts say?

According to Colin Harvey, professor at the University of Pennsylvania’s School of Veterinary Medicine and executive secretary at the American Veterinary Dental College, comparing dogs' mouths to humans' mouth is "like comparing apples to oranges." As Abby found, the microbes in a dog's mouth are very different than those in a human's.

The American Kennel Club elaborates:

"Most of the bacteria in your dog’s mouth aren’t zoonotic, which means you probably won’t get a disease from a big old doggy kiss. There are exceptions to this. Dogs that eat a raw diet are at an increased risk of contracting salmonella, which can be spread to humans. You also probably shouldn’t share kisses with a dog that regularly raids the litter box.

In other words, kissing your dog is less risky than kissing another human, but that doesn’t mean that your dog’s mouth is necessarily cleaner than a human’s—they just have a mostly incompatible set of germs."

 dogs, dog mouths, dog kisses, dog teeth cleaning Keep your dog's mouth clean with regular teeth brushing.Photo credit: Canva

Keeping your dog's mouth healthy through regular teeth cleaning and dental check-ups can also help prevent issues that could potentially come from dog licks.

So there you have it. If your dog doesn't eat a raw diet and doesn't go snacking in the cat box (or some other equally fecal-bacteria-ridden place), their kisses are probably not going to hurt you. Guilt-free pooch smooches for the win!

This article originally appeared in April.

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Animals & Wildlife

Why have we domesticated some animals but not others? It comes down to four F's.

An entertaining video explains why we can't ride zebras or breed "war bears."

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Horses were domesticated over 5,000 years ago. Zebras, never.

Humans have domesticated several kinds of animals over the millennia, from trusty horses and mules to livestock for milk and meat to our favorite furry companions. But why those specific animals and not others? What is it that led us to those particular choices? Why can we ride horses but not zebras? Why don't we purposefully breed "war bears" to fight for us?

That last question comes straight from the always-interesting and often-hilarious CGP Grey, whose YouTube videos explore all kinds of things we wonder about but don't necessarily take the time to research. In the video "Why Some Animals Can't Be Domesticated," Grey explains the four main elements that make an animal a good candidate for domestication, which excludes bears (and many others) from the list.

Grey alliterated the four elements to make them easier to remember: Friendly, Feedable, Fecund, and Family-Friendly. Let's dig into what those mean.

 

  - YouTube  www.youtube.com  

 

Domestication requirement #1: Friendly

This one is fairly self-explanatory, but basically an animal has to not post an inherent, immediate threat. We have to be able to catch them if we're going to domesticate them, so that eliminates all of the "carnivores whose day job is murder" as Grey puts it, as well as the large, nervous prey animals that are too afraid of us to let us get anywhere near them.

 wild animals, domesticated animals, gazelle Good luck trying to catch a gazelle.Photo credit: Canva

Domestication requirement #2: Feedable

Every animals is feedable, of course, but that doesn't mean it's easy or cheap to feed them, especially in large numbers. This category pretty much eliminates pure carnivores and some omnivores, leaving mostly herbivores (and some unpicky omnivores) that are easy and cheap to feed. And that aren't dangerous (see #1).

 wild animals, domesticated animals, chickens, chicken feed Chickens will eat just about anything.Photo credit: Canva

Domestication requirement #3: Fecund

This requirement is all about breeding and babies. Some animals are extremely slow to breed, like pandas and elephants, making them undesirable candidates for domestication. Animals that have mate frequently and have relatively short gestation times and/or large litters are more suited to domesticated life. They also need to grow up quickly, which also takes elephants out of the pool.

However, as Grey points out, humans can still tame other animals like elephants. But taming is not the same as domesticating. The basic rule is: If it's on a farm, it's domesticated. If it's in a circus, it's tamed.

Domestication requirement #4: Family-friendly

This is where the horses and zebras question comes in. Horses were domesticated in Eurasia, but if humans started in Africa, why weren't zebras domesticated first? Grey explains that while horses tend to live in hierarchical herds, zebra are more independent with no family structure. Humans can capture the lead male horse and get the rest of the herd to fall in line. Zebra herds are more of a free-for-all and they're kind of jerks to even one another.

 horses, zebras, domesticated animals, wild animals There's actually a big difference between horses and zebras besides just the stripes.Photo credit: Canva

Barnyard animals have inherent family structures that humans have figured out how to fit into. These animals learn to see the humans who own them as a lead cow or top chicken or whatever.

Way back in the hunter-gatherer age, when humans were just figuring out animal domestication, animals had to have all four of these requirements. Today, we have the ability and technology to domesticate more animals if we want to, but we also have less of a need to. Some breeds of foxes have recently been domesticated, bred to be friendly with humans. How fun would it be to have a pet fox?

  - YouTube  www.youtube.com  

 

Technically, a lot more animals could be domesticated if people really wanted to put in multiple human lifetimes of time and effort, but why?

You can follow CGP Grey on YouTube for more fun and informative videos.

This article originally appeared in April.

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Ocean Wise
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Sustainability

Amazing ocean facts you never learned in school

Not even Captain Ahab knew this much about marine life.

Photo by Milos Prelevic on Unsplash
brown fish beside coral under body of water

The ocean covers more than 70 percent of our planet—yet there’s so much about it that we don’t yet know. Experts, in fact, believe we’ve only explored about five percent of the ocean so far—meaning that most of it remains completely unseen and undiscovered.

What we do know, however, is that the ocean is truly wise. Not only does it sustain all human and animal life on the planet, the creatures under the sea continue to give scientists insight that can transform human lives as well (just read about the amazing axolotl below to see what we mean).

A happy ocean makes for happy, healthy human beings (not to mention a healthy planet)—so this summer we’re helping our friends at Ocean Wise spread the word that no action is too small—holding a cleanup on a local shoreline, for instance. Learning about our ocean and all its wonders is another step anyone can take for conservation, so buckle in and prepare for a tidal wave of info that will blow your mind.

1. Playing music—specifically, recordings of healthy reef soundscapes—can help grow coral reef populations.

live coralsPhoto by QUI NGUYEN on Unsplash

Healthy coral reef populations are filled with diverse sounds, thanks to the fish, snapping shrimp, and other marine life that live there. Scientists have found that playing recorded sounds of healthy reefs actually attract coral larvae, since the sounds indicate a healthy, vibrant habitat. Using this knowledge, scientists have taken recorded reef sounds, played them near degraded reefs, and in doing so, have increased the settlement rates of coral larvae, helping the coral reefs regenerate.

2. Dolphins like to party with pufferfish.

Photo by Talia Cohen on Unsplash

How’s this for a good time? Dolphins, particularly younger ones, have been known to seek out pufferfish to play games with them, chewing on them and passing them back and forth between each other like a hacky sack. Not only is this entertainment for the dolphins, scientists theorize that they may intentionally be trying to get the pufferfish to give off a neurotoxin called tetrodotoxin (TTX)–which is a chemical they release when threatened. This chemical is highly toxic in large doses–but in small quantities, experts think that it might induce a mild, pleasurable effect in the dolphins, similar to a narcotic. Party on.

3. Male humpback whales are total crooners.

A male humpback whale breaches the water.

Photo by Thomas Kelley on Unsplash

All humpback whales can vocalize, but male humpback whales actually sing.

During mating season, scientists have observed male humpback whales making sounds that are distinctly different from other humpback calls. Unlike other sounds, these songs have a clear structure, and use small, repetitive “phrases” organized in a specific sequence—in the same way humans sing different verses during a song. Even more amazing? Male humpbacks all sing the same song together in “choruses,” in sessions that last from five minutes to several hours.

4. Axolotls have superpowers (and scientists think it could benefit humans one day).

a couple of animals that are in some waterPhoto by T K on Unsplash

Among biologists, axolotls are known for their ability to regrow lost or damaged tissue. When an adult axolotl loses a limb, they can actually grow it back in just a few months time, thanks to a substance they produce called retinoic acid, which plays a large role in regenerating skin cells. (If the name sounds familiar, it’s because retinoic acid is a derivative of Vitamin A, and it’s commonly found in skin creams.) While we already know that retinoic can make our skin look fabulous, scientists are currently studying whether it could someday help human limbs regrow, similar to the axolotl’s.

5. A healthy ocean can help reverse climate change

green algae underwater photographyPhoto by Brian Yurasits on Unsplash

The ocean generates half of the oxygen we breathe and absorbs nearly a third of the world’s carbon emissions. Phytoplankton, the microscopic algae that float near the ocean’s surface, are a big part of the reason why. But there’s another unsung hero—kelp. Unlike phytoplankton, kelp are large seaweeds that grow in dense underwater forests along coastlines, absorbing CO2 and supporting ecosystems. Ocean Wise is helping bring back these powerful carbon sinks one kelp forest at a time.

Help us #BeOceanWise by doing one small thing for ocean conservation in your community (because just one thing can start a huge wave of positive change). Visit ocean.org for tips and tricks to keep our oceans healthy because no action is too small.

Science

A scientist created a 'utopia' for mice and then they all started dying

The results are fascinating, but are they relevant to humanity?

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How could Mouse Heaven go so terribly wrong?

In 1968 John Calhoun, a scientist and animal behavioralist, decided to create a "utopia" for mice. It would have unlimited food and water, with beautiful nesting spaces and plenty of materials for the mice to make cozy homes with. Sweet experiment! the mice were probably thinking. Much better than the Maybelline trials we're used to.

However, there was a catch, of course. There was one thing the utopia would be lacking, and that would be physical space. As the mouse population grew, overcrowding would become an issue, and Calhoun wanted to study the problems this would potentially cause. That sound you hear is the collective sigh of the disappointed mice who were stoked about the 24/7 all-you-can-eat buffet.

The experiment, dubbed Universe 25, began when Calhoun introduced four mouse "couples" into the utopian complex. A year or so later, it was overrun and the conditions had turned hellish, even though the mice had not run out of food or water.

mouse, mice, animals, science, research, studies"The conditions had turned WHAT?"Giphy

Initially, for just the eight original mice, the square box Calhoun built included 256 nesting boxes (or apartments) stacked on top of one another. Water bottles and food dispensers were located all along the nesting spots, and mice could travel throughout the complex at will via mesh tunnels. The starter mice were also screened for diseases and the population was obviously protected from predators. The climate was controlled and comfortable. Conditions were perfect.

The first mouse pups showed up a little over three months later, with the population of the colony doubling every 55 days. Nineteen months later, there were 2200 mice living inside the box. With such perfect surroundings, the infant mortality rate was practically zero, leading to the rapid rise in numbers.

mice, mouse experiments, scientific research, animal experiments, overpopulationJohn Calhoun poses with his rodents inside the mouse utopia.Yoichi R Okamoto, Public Domain


By month 19, this rodent utopia had become an overcrowded hellscape. Calhoun noticed three alarming trends, in particular.

In short, everything was devolving into chaos and the very society of the mice began to collapse at a rapid rate.

The "Beautiful Ones" and the "Dropouts": Mice have a complex social hierarchy ruled by dominant alpha males. Sam Kean of Science History Institute Museum & Library notes that, in the wild, non-dominant males (the ones who lose macho showdowns) can skip town and start over somewhere else. But in the close quarters of Calhoun's experiment, with nowhere to hide, they were forced to hang around and viciously battle with each other over scraps. Eventually, non-dominant male mice, which Calhoun called the "Beautiful Ones," withdrew from society completely and only ate, slept, and groomed themselves.

Though resources were unlimited, certain aggressive males hoarded them anyway: The alpha males ruled over everything in the once-utopian mouse society. They kept harems of females in the apartments to mate with and fought fiercely to defend their territory. But new waves of hungry young male mice kept coming and coming, and eventually even the most dominant alphas abandoned their posts. This led to more attacks on nursing females, which in turn led to more mothers kicking their pups out of the nest early.

Birth rate declined dramatically: With the non-dominant males giving up completely and focusing on #SelfCare, dominant males too exhausted from endless battles, and females sick and tired of it all (many became asexual hermits by the end), stopped mating and giving birth entirely. Once this happened, the society was doomed. Even with plenty of food still available, cannibalism was rampant.

Calhoun was not shy about drawing parallels between his research and humanity. "I shall largely speak of mice, but my thoughts are on man, on healing, on life and its evolution," he once wrote.


mice, mouse experiments, scientific studies, universe 25, sociology, overpopulationAlpha male mice, anyone? Photo by Kanashi on Unsplash

There are aspects of his wild experiment that certainly sound familiar.

We live in a world with plenty of resources for everyone, but a few select people hoard more than their fair share. When you think of the rodent "apartments," it's hard not to picture densely packed urban environments where people are stacked on top of each other at every turn. Maybe on some level some of us can relate to the “Beautiful Ones” and their urge to not participate in all the ugliness and just sequester and groom themselves. You can make an argument that when the mice stopped having to worry about food and shelter, it removed the element of challenge from their lives and left them lost–like many of us are lucky enough to not have to wonder where our next meal comes from, and maybe that has something to do with our never-ending search for meaning. Some even go so far as to link more people choosing to delay having children, or not have children at all, with the collapsing society of the mice.

But Calhoun's work has also been heavily scrutinized, with some claiming it's based on shaky science. And in the end, there’s the small matter that humans are not mice. We are infinitely more complicated, and so much better suited to adapting to our environments. Kean writes, "Ultimately Calhoun’s work functions like a Rorschach blot—people see what they want to see."

It's fascinating and thought-provoking nonetheless.

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