Every dog has its day, and July 14, 2004, belonged to a boxer named Tasha. On that date, the National Institutes of Health announced that the barrel-chested, generously jowled canine had become the first dog to have her complete genome sequenced. “And everything has kind of exploded since then,” said Elaine Ostrander, a canine genomics expert at the National Human Genome Research Institute, who was part of the research team.

In the 20 years since, geneticists have fallen hard for our canine companions, sequencing thousands upon thousands of dogs, including pedigreed purebreds, mysterious mutts, highly trained working dogs, free-ranging village dogs and even ancient canine remains.

Research on canine cognition and behavior has taken off, too. “Now dog posters are taking up half of an animal behavior conference,” said Monique Udell, who directs the human-animal interaction lab at Oregon State University. “And we’re starting to see cat research following that same trend.”

Just a few decades ago, many researchers considered pets to be deeply unserious subjects. (“I didn’t want to study dogs,” said Alexandra Horowitz, who has since become a prominent researcher in the field of canine cognition.) Today, companion animals are absolutely in vogue. Scientists around the world are peering deep into the bodies and minds of cats and dogs, hoping to learn more about how they wriggled their way into our lives, how they experience the world and how to keep them living in it longer. It’s a shift that some experts say is long overdue.

“We have a responsibility to deeply understand these animals if we’re going to live with them,” Dr. Udell said. “We also have this great potential to learn a lot about them and a lot about ourselves in the process.”

Pet projects

For geneticists, dogs and cats are both rich subjects, given their long, close history with humans and their susceptibility to many of the same diseases, from cancer to diabetes.

Dogs have been an especially appealing target. Intense human selection, especially over the last few centuries, has created a staggeringly diverse collection of canines, from Chihuahuas to Great Danes, and hundreds of reproductively isolated breeds, which often suffer from high rates of disease.

In the 2000s, scientists identified the genetic underpinnings of a variety of canine traits, including curly coats and bobbed tails. They pinpointed mutations that could explain why white boxers were prone to deafness. And they found that corgis, basset hounds and dachshunds owed their stubby legs to a genetic aberration in a family of genes that also regulates bone development in humans.

These early studies “highlighted both the potential that we could learn from dogs, but also that we were going to need bigger sample sizes to do it really well,” said Elinor Karlsson, a geneticist at UMass Chan Medical School and the Broad Institute. And so, researchers began creating large citizen science projects, seeking DNA samples and data from dogs across the United States.

Pet owners rose to the challenge. The Golden Retriever Lifetime Study, which began recruiting in 2012, has been following more than 3,000 dogs in an effort to identify genetic and environmental risk factors for cancer, which is especially common in the breed. Since 2019, the Dog Aging Project, a long-term study of health and longevity, has enrolled nearly 50,000 dogs.

Dr. Karlsson’s own project, Darwin’s Dogs, is at 44,000 canines and counting. (Some 4,000 have had their genomes sequenced.) Researchers are mining the data for clues about bone cancer, compulsive behavior and other traits. Among the early findings: Although many behavioral traits, such as sociability and trainability, are heritable, they are widely distributed across the canine kingdom, and breed is a poor predictor of an individual dog’s personality.

This spring, Dr. Karlsson unveiled a much-anticipated expansion: Darwin’s Cats. “I’m a total cat person — have never owned a dog,” she said. Later, in an email, she added, “I’d love to know if ‘cat sleeps on your head’ is influenced by genetics.”

Data drivers

These projects were made possible as genomic sequencing got faster and more affordable. But the “tremendous enthusiasm” of pet owners has been integral, said Dr. Ostrander, who now leads the Dog10K project, an effort to build a comprehensive global catalog of canine genetic diversity.

Today’s dog owners know more about genetics and are highly motivated to participate in research. “People devote extraordinary amounts of time and money to canine health and canine care,” she said. “We care deeply that they live the best life they possibly can.”

The pet-health industry has blossomed and is producing data of its own. At Nationwide, which provides health insurance for pets, a veterinary analytics team has been combing through millions of claims to document the health problems common in dogs and cats of different breeds, sizes and ages. Mars Petcare, which owns multiple veterinary chains, hopes to recruit 20,000 canine and feline patients to contribute biological samples to a companion animal biobank.

The research also promises to inform human medicine. Dogs and cats share many of our genes, of course, but they also share our homes. “They’re not a mouse living in a cage,” said Dr. Kelly Diehl, a veterinarian who directs science communications for the Morris Animal Foundation, which is conducting the golden retriever study.

That makes pets good models for studying environmental and lifestyle influences on health. For instance, one team of golden retriever researchers is looking for links between pollutants and lymphoma. Early results from the Dog Aging Project suggest that dogs with active lifestyles are at decreased risk for “doggy dementia” and that living in a social environment, such as a home that includes other pets, may be good for canine health.

“The big overarching question is: What are the biological, environmental and lifestyle factors that influence healthy aging in dogs?” said Daniel Promislow, a biogerontologist at the University of Washington and a co-director of the project. “That is a fundamental major question for people, as well.”

Dog days of psychology

Several decades ago, scientists seeking to decipher animal minds typically studied wild, big-brained creatures, like great apes and cetaceans, or laboratory stalwarts, such as rodents and birds. Those animals that napped on our couches? “People really were not thinking about dogs as true animals,” said Dr. Horowitz, a canine cognition researcher at Barnard College. “Because they were in our homes, and they’re domesticated — like, they were so adulterated that they weren’t interesting.”

But in the late 1990s and early 2000s, two research teams reported that dogs were gifted at interpreting human cues, successfully following human pointing gestures and eye gazes to locate hidden food. On these tasks, they outperformed wolves raised by people and even, in some cases, great apes. The studies suggested that dogs possessed sophisticated forms of social cognition, and researchers sat up in attention.

“The wind has changed,” said Adam Miklosi, a canine cognition researcher at Eotvos Lorand University in Budapest, who conducted some of the foundational studies. “The dog community is one of the biggest communities in cognition research.”

Additional research has since added detail and nuance to those early studies, highlighting both the capabilities and the limitations of the canine mind. The data generally confirm that dogs are skilled at social tasks and highly attuned to human cues. But the science also suggests that we are sometimes too eager to project our own experiences onto dogs. When dogs display what many people describe as a “guilty look” — averting their eyes and slinking away from their owners, perhaps — they are probably responding to being scolded, not feeling regret over a misdeed, Dr. Horowitz found.

The field blossomed, in part, because dogs were cooperative, convenient and affordable subjects. Why trek into the wild or house hundreds of animals in a lab? Canine cognitive scientists could simply borrow the approach of developmental psychologists.

“People who do developmental psychology don’t have labs full of 12-month-olds,” said Evan MacLean, the director of the Arizona Canine Cognition Center at the University of Arizona. “They have phone numbers of parents. We have the phone numbers of dog parents.”

That approach made canine cognition research feasible for scientists at colleges and universities without big research budgets, he said. And as the field has grown, it has opened up opportunities for larger, more collaborative efforts. For the ManyDogs Project, scientists in labs around the world are now working to “stress test” some key findings in canine cognition, said Dr. MacLean. “If we have important results, we feel like we should be able to replicate these things in labs around the world.”

Cats as catch can

Until recently, scientists took little interest in the social cognition of cats, which did not descend from highly social animals and were often viewed as aloof. But emerging research suggests that some cats, at least, have plenty of social acumen, including the ability to pick up on human emotions and follow human gazes.

One question is how cats come by these abilities. “Do they understand human emotions and follow human cues only if they’ve been exposed to humans early on?” said Jennifer Vonk, a comparative cognitive psychologist at Oakland University. “Do they have to be raised with littermates?”

Perhaps our perception of cats as independent (and sometimes intransigent) is a self-fulfilling prophecy, Dr. Udell said. She noted that kittens are not typically given the same socialization and training opportunities that puppies are. Maybe those enrichment opportunities would help cats show off exactly what they are capable of.

Dogs and cats have become supremely successful at navigating the human world, but deepening our relationships with them might require understanding them on their own terms.

“They have their own drives and desires and needs and ways of understanding the world,” said Clive Wynne, a canine-behavior expert at Arizona State University. “And it’s a beautiful miracle that their way of understanding the world, especially the social world, and our way of understanding the world can be melded together into this really very beautiful partnership.”