by Alexandra Horowitz

The puppy I know — the young sprite we adopted at 8 weeks, whose life I’ve observed since her birth — is changing again. Quid is 6 months old and just seemed to be settling into our family of three people, two older dogs and a cat. But all at once, she is more sensitive. She has begun to startle at perfectly normal things. A container of laundry soap on the floor prompts ferocious barking (deterring the soap not at all). Even after a peaceful introduction to the bottle resting innocently on its side, she remains unconvinced that it is not a threat. My son lying on his stomach, rhythmically kicking the closet door behind him, causes Quid to run under my chair with fear. The vacuum, which she formerly followed around like a duckling would her mother, suddenly concerns her.

Paired with her sudden phobias, Quid is vigilant and unexpectedly headstrong at home. She monitors the activities of the house with both ears, her right turned back to catch what is happening in the kitchen, her left toward me across the room — and her eyes on the dogs in front of her. Every passing car must be barked at. Loudly. When the cat, her playmate and occasional sleep mate, sidles up to her and starts licking, Quid snaps at her and walks away. Her previous willingness to heed my request to wait at the door before entering or exiting has turned into a new trick: I ask her to “wait,” and she runs by me. Many mornings when I call her name, she looks right at me and trots the other way. I can almost hear her slamming her bedroom door behind her.

We thought we adopted a puppy, but what we really had on our hands was a teenager.

Adolescence unites fruit flies, lobsters, zebras and humans — only the duration of adolescence for fruit flies is a few days, whereas in humans, it is somewhere between 10 and 14 years. Quid has entered teendom: thought to be, for dogs, from approximately 6 months old (varying by breed) through their second birthday. Just when we thought we were done with sensitive periods of development, another one races in — one woefully understudied by researchers and often completely ignored by dog people.

We ignore it to our detriment: There is good reason to pay heed to this period in dogs’ lives. As is widely acknowledged in humans, adolescence is a distinct stage of development. No longer a child but far from an adult, the adolescent enters a time of risk-taking, social and sexual experimentation and changeable emotions. No one looks at a 14-year-old boy’s oddly distant yet needy behavior, his increasing independence and quarrelsomeness, and wonders what bit him. We know what bit him: He is a teenager.

But with dogs, we call them “puppies,” then move straight to calling them “adults,” neglecting the elaborate stages of development in between. While one might expect adolescent human children to possibly not “come here” with alacrity when called, or not to do the dishes or clean their rooms when asked, an adolescent dog suddenly refusing to come when called disposes people to say, “Oh, you’re a bad dog,” rather than, “Oh, you’re going through a phase.”

What is called “disobedience” seems to rise during this time: “a passing phase of carer-specific, conflict-like behavior,” as one study gently puts it. Dogs who have learned to sit on command as puppies are less likely to do so as adolescents — and even then, mostly when a stranger, not their person, asks. How perfectly teenage of them. They may be aggressive to other animals, aggressive to people; they destroy things.

While there is a license granted to puppies to err as they grow, to get things wrong now and then, the expectations for their performance grow faster than they do. A primary reason for abandoning dogs in shelters is behavioral — they jump, bite, escape, soil the house. And there is a severe uptick of relinquishments during adolescence, partly because of the uptick of these behaviors; such relinquishments are notable, since euthanization is still the outcome for many returned or unadopted dogs. “Simply being an adolescent can count as a fatal condition,” write Barbara Natterson-Horowitz and Kathryn Bowers, the authors of “Wildhood,” a book about the vast territory between childhood and adulthood across species.

Puberty can mark the beginning of canine adolescence. Distracted by dogs’ newfound fertility, we might miss that it also kicks off a period of rapid growth. They bound from half to nearly all of their final weight from puppyhood to late adolescence. They reach nearly their final height at the shoulder by 7 months. The increase in hormones that leads to a dog’s sexual maturation and a growth spurt also has secondary results, including increased sensitivities and less self-control. Adolescence in mammals also oversees a rewiring of the brain — especially in the areas of the cortex that regulate emotions and make judgments. The result is a changed mind and body; along the way, there can be turbulence. “Like waking up in your tent in the wilderness in a gale force 10,” as the trainer Sarah Fisher has described it — both for the pups and for their people.

What happens next can affect their later behavior. Research has connected events and living situations of early adolescent dogs with various personality traits and behaviors as young adults. For instance, being isolated (in a kennel or left alone outdoors) or injured (through punishment or attack) during this time has been connected to later problems interacting with other dogs or people. Dogs who have been threatened or attacked by an unknown dog are significantly more likely to be fearful or aggressive to dogs as young adults; similarly, being frightened by a person (known or unknown) during adolescence leads to more fear toward strangers.

Adolescence is an opportunity to improve dogs’ fate, as well. At least in research with rats, having an enriched environment in adolescence completely undoes the negative effects of the early life stressor of being separated from their mothers. It is not outrageous to think “environmental enrichment” might be just the experience any dog who was raised in a puppy mill or who had another adverse start to life needs.

Adolescent dogs are trying to expand their worlds, to become more adult — hence the balking at their person’s ostensible “authority.” Adolescent wolves may leave their natal pack at this stage. Notably, their puberty is very much delayed compared to that of dogs, arriving at about 22 months. They may be more equipped, physically and mentally, to skedaddle; still, one wonders if there is a vestigial urge in their domesticated cousins to leave the den.

Pups starting this growth spurt might become sensitive to touch, alternating between shying from and clinging to people; they may start climbing or jumping on people or things. An increase in climbing furniture is not just a challenge to the rules (in homes with rules about such things); it is also a sign of a vestibular system challenging itself. There might be more chewing of objects and licking. All of these acts might read as misbehavior, but in some cases they may actually be a way of managing the situation: chewing, for instance, may help lower stress hormone levels. Adolescent dogs may experiment with their voices, adding new vocalizations — the child testing out what happens when he mumbles or screams. An adolescent wolf howls at a lower pitch than a pup, a kind of analogue to a boy’s sudden voice drop.

As at so many times during early life with dogs, patience is due. It is just a phase. Six months into her life, Quid has gone from a blind, deaf newborn, unable to regulate her own body temperature, barely able to lift her giant head and dependent on her mother for everything, to an exceptionally keen, sprightly member of a human household. She can now hear a spoon scraping the last bits of yogurt from the bowl a floor away, sending her racing in to lick the remnants; she plays gymnastically and generously with both the larger dogs and the smaller cat; she leaps neatly up on the sofa and gazes with avidity at our faces. And so as she runs right by me, tail wagging mightily, while I call her name, I smile at her impulse and mischievousness. I’m witnessing her becoming herself.

Dr. Horowitz, a cognitive scientist who studies dogs, is the author of “The Year of the Puppy: How Dogs Become Themselves,” from which this essay is adapted.