Whether it’s a whimper when they need to pee or those classic puppy eyes when they want food, dogs have many tactics for communicating with their owners.

What we may not realize, however, is the intentionality behind some of these actions.

Researchers have probed this world of dog communication — which has evolved over thousands of years in domestication with humans — and are beginning to interpret their barks and ploys for attention.

The Basis of a Dog Barking

While dog barks may seem simple to an untrained ear, they are a lot more complicated than one may think. Those who listen closely can learn to hear the difference.

A unique study published in Animal Behavior researched the types of dog barks back in 2004. In that work, a team placed six different breeds in three different situations: one where a stranger rang the doorbell, another where the dog was isolated from its owner in a separate room and one where either two dogs or a human and a dog played together.

The results were fascinating. In disturbance situations (scenario No. 1), the dogs were more likely to release lower toned barks. In isolation and play situations, the barks were more commonly a higher pitch.

“[There are] a couple studies that show acoustic differences in barks. The aggressive barks are lower pitched, and the playful or fearful barks are higher pitched,” says Leah Nettle, a dog and cat behaviorist, who was not involved with the 2004 research.

The frequency of a dog’s bark, Nettle says, may also vary depending on how the dog is feeling. While an aggressive bark is likely to be singular or more sparse, the excited, high-pitched expressions will involve many barks.

Why Does My Dog Bark so Much?

While a dog’s barking is sure to get on our nerves at times, we don’t know if barking annoys a dog itself. However, a dog’s barking can impact other dogs.

“Dogs will use body language to show that they’re stressed and use vocal communication to either get their owner’s attention or ward off things,” says Nettle.

In studies involving animal shelter settings, barking is used as an indicator of welfare in dogs. “All the loud noise in a shelter setting is stressful for dogs and can be physically horrible for them,” says Nettle.

Stressed Dogs

Beyond shelter settings, dogs will often mirror stress that their owners feel. In 2019, a study published in Nature found that over long periods of time, a dog will synch up its stress levels to match its owner. In other words, if the owner is upset, the dog will likely match that emotion.

To measure dog and human stress levels, researchers in the 2019 study examined both human and dog hair cortisol concentration, or HCC. The results suggested a strong tie between human HCC concentration and their own dog’s HCC concentration.

Researchers used certain models to analyze the effect of human HCC on dog HCC. Both dog breed and sex were included in the models to reduce possible confounding variables.

“Human HCC had a significant effect on dog HCC for both summer and winter samples. With an increase in human HCC, there was an increase in dog HCC,” researchers wrote in the study.

While dogs’ personalities had little effect on their HCC, the human personality traits of neuroticism, openness and conscientiousness had a significant impact on dog HCC. In other words, a dog’s stress levels would shift based on whether their owner was more or less neurotic, open and aware of their surroundings.

Read More: What To Do If Your Pet Is Struggling With Anxiety

The Evolution of Dog Communication

Believe it or not, a dog’s bark didn’t just appear one day. Unlike other pets, dogs are unique in that they have co-evolved with humans over several thousands of years. The earliest signs of domestication are found 33,000 years ago and completely domesticated dogs are common in the archaeological record beginning around 15,000 years ago.

“Dogs are unique in that they co-evolved with humans and we’ve also domesticated them, so they do have vocalizations that do seem to correspond with domestication,” says Nettle. “Dogs and wolves share a most recent ancestor, and dogs will bark more than wolves do and in more contexts, so it seems like their communication kind of is because of humans.”

Read More: How Does Your Dog Understand You?

Evolution of Dogs: The Shift from Wolf to Dog

The domestication process of dogs was likely a tedious one.

It is unlikely that early human hunter-gatherers were stealing young wolf pups and raising them on their own, according to a 2021 study in Current Biology. It’s more likely that domestication occurred slowly, possibly by accident, as wolves became acclimated to humans while scavenging animal carcasses.

That 2021 study found that wolf pups, no matter how well trained, still act like wolves.

Domesticated dogs, meanwhile, show early emerging social skills that are likely a result of domestication changing their cognition. These social skills include communicating with their owners through barking and some non-verbal gestures.

Dog Body Language

Dogs rely on using gestures to communicate with their owners. Dogs can spontaneously use novel and arbitrary gestures, such as using physical markers.

Additionally, dogs that are better at interpreting human gestures are more successful as assistance dogs. “This interspecific communication is unusual: Dogs are more skilled at using human gestures than mother-reared chimpanzees and other great apes,” researchers wrote in the study.

The next time you hear your dog let out a yap, give it some thought. There’s a good chance they’re trying to get your attention.

Read More: How Dogs Perceive Time