History of Service Dogs

If you are specifically looking for the history of US dog laws, the short answer is that in the United States, service dogs weren't legally recognized until the Americans with Disabilities Act (ADA) was passed in 1990.

The following is a chapter in our award-winning book, "Service Dogs: The Rescue and Training of Heroes." History.com even used our chapter in the creation of their short page about the history of service dogs!

Have you ever wondered why dogs and people have such a special connection? The answer may be that, in many ways, we can think of the history of dogs as the history of people..

Now, the theories that I’m going to be relating here are some of the most current—but you should know that most theories end up being supplanted by new theories. So this is only one interpretation of the history of people and dogs. Theories change all the time, and some theories are controversial. Scientists don’t always know when certain things happened. So what you’ll read here is only one theory of how humans and dogs developed. But if it's true, it's a nice framework for thinking about dogs and how they help people.

The first archaeological evidence of dogs is a 10,000-year-old grave containing the remains of a woman and a puppy,[1] She must have loved her dog very much. DNA evidence confirms that dogs have been around for tens of thousands of years. Unfortunately, whether it’s 30,000 or 80,000 is still unclear.[2]

During the Paleolithic era, people lived a vastly different lifestyle: They lived in small groups, were active all day, and ate non-processed foods. Human bodies adapted to thrive in this outdoor, active lifestyle. However, today we generally lead indoor, inactive lives that are inherently unhealthy—our bodies haven’t had time to adapt to this way of living. Obesity and a variety of other physical and psychological issues have cropped up over the last 10,000 years as a result.

By contrast, dogs remain active and social (when given the chance). Their needs are more basic, and when we pay attention to our dogs’ needs, we end up focusing more on our own pure "primal” needs as well. Every time we choose to walk a dog instead of playing a video game, or when we choose to play “tug” with a dog instead of checking our email, we are satisfying the needs of our own bodies and minds as well as satisfying the wonderful primal needs of our dogs.

Thus we move into the subject of dogs. But first—wolves.

History of Wolves (and Families of Wolves)

We don’t know exactly when wolves evolved into dogs, but let’s start with 200,000 years ago, at the time many scholars think that humans first evolved into their modern form. Think of this time as something like “caveman” time, because humans had "tool use ... and fire use."[3] At that time, "Paleolithic canids [were] definitively wolves and not dogs."[4]

Note: New research indicates that gray wolves don’t live in violent groups called packs; rather, they live in loving, peaceful groups that are actually families. Families can have conflict, but they also love each other. What’s important to realize about wolves is that the “old school” theory of domination—you know, the one where the alpha wolf is dominant and the beta wolves are submissive—comes from observing wolves in confinement that are not living in family groups. Instead, zookeepers place unrelated wolves together in an artificial enclosure, and thus, sadly, aggression starts developing in the group. This aggression, and the resulting dominance and submission, are all artificial; this situation would never come up in the wild. And now that scientists are doing more studies of wolves in the wild, they’re realizing that wolves are much more family-oriented than previously thought. When we think of dogs, we should keep this more loving “family” model in mind.

Wolves to dogs

Scavenger wolves evolved into scavenger dogs. (Illustration from The Quadrupeds of North America by John James Audubon and John Bachman.)

The Beginning of Wolves Living With People

At some point, perhaps around 40,000 years ago[5] or 80,000[6] years ago—scientists aren't sure exactly when—"the human lineage underwent a genetic change that boosted the brain's cognitive powers ... what some have called a 'human revolution.'"[7] Many scientists think there was a dramatic genetic change in brain function—a cognitive revolution that is pretty amazing. This was a huge shift in human development that "raises the further question of why there was a delay of some 100,000 years between anatomical modernity and perceived behavioral modernity."[8] What was this dramatic genetic change in brain function? Well, it might be improved memory, or it might be improved language skills—we don’t really know. But there is another theory that maybe this big change happened as a result of the domestication of dogs. Just as wolves started changing as they hung around people and scavenged for food, humans started changing at that time, too...and possibly, the two changes are connected. "It just might be that dogs have done much, much more than that for humankind. They may have saved not only individuals but also our whole species, by 'domesticating' us while we domesticated them."[9] I just love this idea, that people and dogs have evolved together, been partners, and have lived in a symbiosis that still works, even in today's modern world. One problem with this theory is that not only are we not sure when the human cognitive revolution happened, we’re also not sure when dogs started being domesticated. Was it 10,000 years ago (as per the archeological evidence), or 80,000 years ago (as DNA evidence suggests)? There are a lot of different theories among scientists—so it may or may not have happened at the same time as this dramatic genetic change in human brain function. But if it was at the same time, that would be pretty intriguing. Once dogs were around, suddenly people didn’t have to worry about being surprised by an animal attack in the middle of the night, because dogs would warn them of impending danger. With dogs, humans could hunt rabbits and birds more easily. And with dogs, they didn’t have to worry about trying to hear and smell and see things that were difficult to hear and smell and see—such as wild animals or other tribes—because the dogs would do that for them. It’s an interesting theory, and if it’s true it means that dogs and humans started becoming closely connected a long, long time ago.

Native American woman with her dog

Dogs helping Native American women haul items, each using a "travois." From Provincial Archives of Alberta.

How Dogs Developed

The domestication of dogs changed scavenger wolves into a subspecies that was one breed. Basically, dogs were all a kind of dingo—"the dingo in Australia and the 'singing dog' in New Guinea represent, in ever-dwindling populations, living, purebred relics of the first domestic dogs."[10] 


What does a "generic" dog look like? Luckily, we have the answer: the above dingo is what dogs look like if they're not separated into breeds. (Image from Wikipedia Commons, shot by Benjamin444 at taken at a wildlife sanctuary/rescue center in South-eastern Australia.)

Sidebar: How were these new dogs different from wolves? Scientists disagree, but at least some state that wolves and dogs are both Canis lupus, but the scavenger wolves were becoming Canis lupus familiaris (dogs), and thus "Domestic dogs, the only large carnivore ever to be domesticated, were derived from wolves (Canis lupus)."[11] In fact, Canis lupus, the wolf, is basically identical to the domestic dog, and "the two share 99.9% of their DNA."[12] With this model, both dogs and wolves are the same species; it’s just that dogs are a subspecies. Some scientists are finding evidence that "dogs are neotenic"[13], meaning that they are a little bit like baby wolves—with shorter snouts and cuter eyes, less aggression, and more playfulness. The diet of wolves and dogs is a bit different, too. Whereas wolves are "true carnivores,” … “modern-day dogs differ in several digestive and metabolic traits that appear to be more associated with omnivorous such as man, pigs, and rats."[14] It remains to be seen whether dogs require any carbohydrates, but as “descendants of the decidedly carnivorous gray wolf, [they] still retain a preference for meat though they live on carbohydrate-rich resources."[15] A more dramatic difference, though, is that dogs definitely have smaller brains than wolves--and that's a good thing. This smaller brain is a result of dogs having less fear (and, thus, less aggression), and is sometimes called "the tameness hypothesis.”[16] With less fear and aggression, dogs don’t need that part of their ancestors’ brain that produces these emotions, and thus the dog's brains are smaller. Thank goodness--we like dogs to not have all that brain space devoted to fear or aggression!

Bottleneck effect

Images from textbook content produced by OpenStax (Rice University) and from TedE on Wikipedia.

An unfortunate part of this evolutionary process is that dogs came from a pretty small subset of wolves—it was just a few wolves that started hanging around people and getting domesticated. This genetic bottleneck, sometimes called the "Wright's bottleneck effect"[17], resulted in dogs having less genetic diversity than wolves. Even today, wild dogs such as dingoes or village dogs still get cancer and other diseases at a much higher rate than wolves ever did. And of course the breeds of domesticated dogs—which have even less genetic diversity—get even worse diseases, such as breed-specific cancers.

Agricultural Revolution (And All the Other Domesticated Species)

Back to the human timeline--with cats and horses and other animals!

It can be said that after the "cognitive revolution," the next important thing that happened was "the beginning of the Agricultural Revolution 10,000 years ago."[18] With the onset of agriculture and farming, the domestication of many other animal species began. This is where written history really begins. With the onset of written language, a numeric system, and city-societies, then llamas and pigs and cows and sheep and horses and cats and all the other domesticated animals began to appear. But dogs are unique among all these domesticated animals because they had already been around for a long time.

Possible History of Dogs and People

The above is a timeline we commission to illustrate the theory that dogs and people evolved together and became a team that benefits each other.

Dog Breeds Start Developing

"Archaeological evidence from ancient Egypt suggests that several types of morphologically differentiated dogs (similar to mastiffs and greyhounds) existed 4000 years ago," but most dogs were mongrels or a cross between breeds.[19] It wasn’t really until "the introduction of the breed concept and the creation of breed clubs in Europe in the 1800s"[20] that purebred dogs became more common. Around that time the Industrial Revolution freed up a lot more time for British and American dog owners, so they started developing hobbies, such as dog breeding. Kennel clubs became hugely popular, and canine enthusiasts started breeding dogs for the specific looks that the kennel clubs deemed to be the standard traits of those breeds. For the first time, for instance, people who didn’t raise sheep had the time and money to own the smart dogs that shepherds used, and they defined a “breed standard” that all Border collies should ideally look like. Instead of shepherds breeding their favorite herding dog with their neighbor’s favorite herding dog (and winding up with dogs that generally looked alike), breeders started focusing on looks rather than temperament. Sometimes, breeders go a bit overboard, though. Unfortunately, since the more formal definitions of “breed standards” started, poor breeding practices have sometimes caused some breeds to become quite unhealthy. Breed standards "stress that dogs should be bred to bring out the best look in the breed, even though the physical traits of some breeds have detrimental effects on the dogs' health."[21] While I love the breed, the English bulldog, for instance, has been bred from having a haphazard look (by owners who wanted the dogs to fight) to a very specific “smooshed-in” look that produces breathing difficulties in the vast majority of these dogs--so much so that "the bulldog has been banned from plane travel in the cargo hold by many domestic and international airlines due to a high incidence of deaths."[22] We love purebred dogs and often work with them, but these problems are part of the reason why we so often use mixed breed dogs at Pawsitivity (the other reason is that we love rescuing animals).

Service Dogs Developed (At First, Just for the Blind)

So we have different kinds of dogs bred for different purposes. When did people first start training them?

Guide dog harnesses have only been around a couple of hundred years, but people who are vision-impaired have been using dogs for a long time.

  • The first instance we know about is from way back in 74 CE, during the time of the Roman Empire. A frieze was discovered in the ruins of Pompeii that depicts a dog with a blind man.

  • Archaeologists also discovered a scroll, painted sometime around the year 1250, that depicts a dog guiding a man through a busy street in China.[23]

  • A medal created by Italian sculptor Leone Leoni in 1561 portrays a dog leading an old blind man with a cane.[24] 

Art involving guide dogs

The first three examples above aren't much to look at, but my favorite example from the past is this sweet image from the 1700s by Thomas Gaugain showing a young girl who is blind walking through the countryside with her dog (courtesy of the British Museum) and this etching of a fiddler who is blind, assisted by his dog, by R.H. in 1631, (Wellcome Images, a website operated by Wellcome Trust, a global charitable foundation based in the United Kingdom).

In 1780, the Parisian hospital for the blind, Les Quinze-Vingts, started training dogs for people who were blind, although we only know this because of "a painting executed by JeanBaptiste Chardin in 1752 depicting blind inmates of the Quinze-Vingts hospital in Paris being guided by dogs".[24.1] In the years that followed, some hospitals and dog trainers helped patients use dogs, too. So, unofficially, Les Quinze-Vingts was the first school for guide dogs.

Building on the practice of using dogs to help the blind, Dr. Johann Wilhelm Klein wrote a book about harnesses for guide dogs in 1819, "thus introducing an idea which led to the development of the rigid U-shaped harness".[24.2] However, the idea didn’t take off, and no one really used guide dog harnesses for almost 100 more years. 

War and its Aftermath

British helper dog

Sergeant of the Royal Engineers sending a message from the front line. (Image courtesy of the Imperial War Museum.)

In World War I, the Germans and British used brave dogs in various ways to help the war effort, including carrying aid to the wounded in no-mans-land and bringing back the caps of the wounded so that rescue teams could be sent out to find them.[25]

Stubby the War Dog

"Stubby the War Dog" was a stray dog who was smuggled by an American onto a troop transport to the European Theater of WWI. Stubby wound up "serving" with the 102nd Infantry, 26th Division, and it was lucky for them that he did. Stubby not only led medics to wounded soldiers, he alerted his comrades when a German spy tried to sneak past the ranks. After the war, Stubby met with U.S. presidents, marched in American Legion parades, and received honors from the Red Cross and the Humane Society (Photo is Stubby: Terrier Hero of Georgetown, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11296399. The text is from Hoena, B. A., and Oliver Hurst. Stubby the Dog Soldier: World War I Hero. North Mankato, MN: Picture Window Books, a Capstone Imprint, 2015.)

With war comes wounds, and dogs helped veterans (and others) after the World War 1. Germany pioneered the use of dogs to help guide veterans who were blind. By 1927, an estimated 4,000 Germans were using guide dogs![26]

German stamps of guide dogs for veterans

After World War One, Germany issued these stamps in honor of the Oldenberg school for training guide dogs. The images show veterans being helped by their dogs, using both the traditional cane and also a harness for the dog. Some of the stamps use the word, "Fuhrer," but in this context, the word does not refer to Adolph Hitler, but instead, it just means the word "leader". Thus, one of the stamps has the translation (very roughly) translates as "He leads him from sidewalk to sidewalk". (Images courtesy of the Imperial War Museum.)

From Germany to the USA:

Miriam Ascarelli, in her book, Independent Vision: Dorothy Harrison Eustis and the Story of the Seeing Eye, tells the following inspiring story: In 1923, an American woman, Dorothy Harrison Eustis, started breeding and training German Shepherds in nearby Switzerland to work as police and military dogs. Four years later, she wrote a story about the guide dogs in Germany for The Saturday Evening Post. Morris Frank, an American who was blind, wrote to her and asked, “Is what you say really true? If so, I want one of those dogs! And I am not alone. Thousands of blind like me abhor being dependent on others. Help me and I will help them. Train me and I will bring back my dog and show people here how a blind man can be absolutely on his own. We can then set up an instruction center in this country to give all those here who want it a chance at a new life.” Ms. Eustis trained a Guide dog for Mr. Morris, who traveled to Switzerland and was partnered with the dog, a female German Shepherd named Kiss—whom he promptly renamed Buddy (the same name as the next six guide dogs he owned). Eustis later founded the first guide-dog training school in the United States, and in the following years, schools and organizations were founded all over Europe.

Guide dog

In the 1930s the Swiss Army began training dogs for avalanche and snow rescue[27] and in World War II, all sides of the conflict started training dogs for military work.

Miltary Working Dog

Thus, when US soldiers came back from World War II, some of them were experienced dog trainers. Some of these ex-servicemen started teaching classes for civilian dog owners. (Image of this U.S. Army soldier and his military working dog is courtesy of the National Museum of Health, USA).

The Past 40 Years

Dolphin and trainer

A wild animal such as a dolphin cannot be effectively trained through punishment or negative reinforcement, but rather, they are trained through the use of positive reinforcement. Once dog trainers realized the results that these other trainers were getting, the benefits of positive reinforcement and the hazards of punishment became clearer to many more people and then modern dog training methods really took off. 

Military dog jumping from a plane

Both the U.S. military and the Guide Dog Association now train dogs this way. See our page on how we train for more details.

In the 1970s, studies of puppy development revealed the importance of early socialization for puppies. A lack of early socialization is why rescue dogs are often difficult to work with. When poorly socialized puppies grow into adult dogs, the best of training can’t make up for their developmental deficiencies; by then the dogs are way past the “window of socialization” that is available only during puppyhood. While we rescue adult dogs, this fact does complicate their selection. We must be extra careful to test to see that an adult dog received proper socialization as a puppy. 

Check out this article for the story about how Bonnie Bergin trained the very first service dog (other than guide dogs for the blind).

In 1990, the Americans with Disabilities Act (ADA) was passed, and it defined the idea that service dogs could be used to help with conditions other than blindness and deafness.

Guide horse

That's a horse. Really. In this picture, a miniature horse is used as a guide animal for a person who is blind. (Image courtesy of DanDee Shots.)

Originally the ADA originally stated that service animals could be any species, so people in wheelchairs sometimes used monkeys for picking up dropped objects and such. The Americans with Disabilities Act has since tightened their regulations, and the law now states that "only dogs can qualify as service animals. (In a few special cases, miniature horses also qualify)".[29] As the service dog industry continued to grow, organizations were formed to help certify both service dog training organizations and service dogs.  "These membership organizations include Assistance Dogs International, International Guide Dog Federation, and International Association of Assistance Dog Partners".[30]


Hershey, who was one of the first service dogs we trained, practices with a person who is not his trainer. This way, the dog gets used to "generalizing", so that the dog can respond to their handler (and not just the trainers). There are lots more fun videos at our Facebook page. Later on, we even started filming in landscape, not portrait! :-)

Around the 1990s and the 2000s, people started training service dogs to help with a wider range of disabilities. Various species of dogs were trained to assist children and adults with autism, people with diabetes, veterans and others suffering from PTSD, people with other emotional and psychological disorders, and many others. And that’s where we come in!

Pawsitivity Service Dogs

(Image courtesy of photographer Lisa Venticinque.) We don't actually look this cute, it's just that Lisa is a great photographer.


My wife, Julie, and I are a St. Paul, Minnesota couple with no children. Julie (born and raised in Grand Forks, ND) and I (born in Mankato, MN, lived in Hibbing, MN as a youngster, and then raised in St. Louis Park, MN) met at Carleton College in Northfield, MN. Julie and I then went to graduate school (she went to Chicago while I went to Dekalb, IL), but then started dating, fell in love, and got married. We founded Pawsitivity five years ago after a good friend—a single mother who has a child with autism—told us how her son was so helped by his dog that it changed the course of his life. Julie had a psychology degree and had already been doing therapy dog work with our pet dog, Chloe, and she was interested in doing more training to work with service dogs. We discovered that there were no service dog providers in the state that specialized in autism, nor any in any of the surrounding states. Maybe we could train service dogs for children with autism using the same techniques as Applied Behavioral Analysis (positive reinforcement)! Since our mission includes rescuing dogs, sometimes we find that a dog is not appropriate for a child with autism, and then we train the dog for someone with a different disability. The challenges of this mission have, at times, been daunting, and if you want the rest of the story of how we have met these challenges, check the "About Us" page of this website

The Future

Whether you use Pawsitivity or some other organization for your service dog, we think it's important to stick to the following guidelines, all of which Pawsitivity follows:

  1. 501(c)(3) status 
    We believe that a service dog organization should always be run as a nonprofit (not a business) because the board's oversight will keep the organization accountable.
  2. "Meets Standards” certification with the Charities Council and "Gold Level" with Guidestar.org
    We believe that a service dog organization should achieve "Meets Standards" (the highest rating) by the Charities Council and at least "Gold Level" with GuideStar.org to ensure that the nonprofit's actions are transparent.
  3. CPDT-KA certification
    We believe that a service dog trainer should be certified with a CPDT-KA after his/her name because this certification helps ensure that the trainer is experienced.
  4. Positive reinforcement policy
    We believe that a service dog nonprofit should train the dogs using positive reinforcement (just like the policy and techniques that the U.S. Army uses for its military working dogs and the Guide Dogs Association uses for its guide dogs) because this approach is scientifically proven to be faster, more reliable, and will ensure that training will always "do no harm" and not cause fear or aggression. See our page on training for more details.

Boy and his Pawsitivity autism service dog

[1] Day, Leslie Preston. "Dog burials in the Greek world." American Journal of Archaeology 88, no. 1 (1984): 21-32.

[2] Vilà, Carles, Peter Savolainen, Jesús E. Maldonado, Isabel R. Amorim, John E. Rice, Rodney L. Honeycutt, Keith A. Crandall, Joakim Lundeberg, and Robert K. Wayne. "Multiple and ancient origins of the domestic dog." Science 276, no. 5319 (1997): 1687-1689.

[3] Rios-Garaizar, Joseba, Aleix Eixea, and Valentín Villaverde. "Ramification of lithic production and the search of small tools in Iberian Peninsula Middle Paleolithic." Quaternary International 361 (2015): 188-199.

[4] Drake, Abby Grace, Michael Coquerelle, and Guillaume Colombeau. "3D morphometric analysis of fossil canid skulls contradicts the suggested domestication of dogs during the late Paleolithic." Scientific Reports 5 (2015).

[5] Barker, Graeme, Huw James Barton, Michael I. Bird, Patrick Daly, Ipoi Datan, Alan P. Dykes, Lucy Farr, et al. "The ‘human revolution’ in lowland tropical Southeast Asia: the antiquity and behavior of anatomically modern humans at Niah Cave (Sarawak, Borneo)." Journal of Human Evolution 52, no. 3 (2007): 243-261.

[6] Wong, Kate. "The morning of the modern mind." Scientific American 292, no. 6 (2005): 86-95.

[7] Balter, Michael. "What made humans modern?" Science 295, no. 5558 (2002): 1219-1225.

[8] Powell, Adam, Stephen Shennan, and Mark G. Thomas. "Late Pleistocene demography and the appearance of modern human behavior." Science 324, no. 5932 (2009): 1298-1301.

[9] Shipman, Pat. "Do the eyes have it? Dog domestication may have helped humans thrive while Neandertals declined." American Scientist 100, no. 3 (2012): 198.

[10] Clutton-Brock, Juliet. "Origins of the Dog: Domestication and Early History." Chap. 2 in The Domestic Dog: Its Evolution, Behaviour and Interactions with People, ed. James Serpell. Cambridge: Cambridge University Press, 1995.

[11] Hewson-Hughes, Adrian K., Victoria L. Hewson-Hughes, Alison Colyer, Andrew T. Miller, Scott J. McGrane, Simon R. Hall, Richard F. Butterwick, Stephen J. Simpson, and David Raubenheimer. "Geometric analysis of macronutrient selection in breeds of the domestic dog, Canis lupus familiaris." Behavioral Ecology 24, no. 1 (2012): 293.

[12] Grimm, David. "Dawn of the dog." Science 348, no. 6232 (2015): 274-279.

[13] Cohn, Jeffrey. "How wild wolves became domestic dogs." Bioscience 47, no. 11 (1997): 725-728.

[14] Bosch, Guido, Esther A. Hagen-Plantinga, and Wouter H. Hendriks. "Dietary nutrient profiles of wild wolves: insights for optimal dog nutrition?" British Journal of Nutrition 113, no. S1 (2015): S40-S54.

[15] Bhadra, Anandarup, Debottam Bhattacharjee, Manabi Paul, and Anindita Bhadra. "The meat of the matter: a thumb rule for scavenging dogs?" arXiv preprint arXiv:1304.3546 (2013).

[16] Wrangham, Richard, and David Pilbeam. "African apes as time machines." Sect. 1, chap. 1 in All Apes Great and Small. Volume 1: African Apes, eds. Biruté M.F. Galdikas, Nancy Erickson Briggs, Lori K. Sheeran, Gary L. Shapiro, and Jane Goodall. New York: Springer US, 2002.

[17] Federoff, N. E., and R. M. Nowak. "Man and his dog." Science 278, no. 5336 (1997): 205-209.

[18] Simopoulos, Artemis P. "The importance of the ratio of omega-6/omega-3 essential fatty acids." Biomedicine & Pharmacotherapy 56, no. 8 (2002): 365-379.

[19] Sundqvist, A-K, Susanne Björnerfeldt, Jennifer Ann Leonard, Frank Hailer, Åke Hedhammar, Hans Ellegren, and Carles Vilà. "Unequal contribution of sexes in the origin of dog breeds." Genetics 172, no. 2 (2006): 1121-1128.

[20] Parker, Heidi G., Lisa V. Kim, Nathan B. Sutter, Scott Carlson, Travis D. Lorentzen, Tiffany B. Malek, Gary S. Johnson, Hawkins B. DeFrance, Elaine A. Ostrander, and Leonid Kruglyak. "Genetic structure of the purebred domestic dog." Science 304, no. 5674 (2004): 1160-1164.

[21] Templeton, Regan. "Tough love: how breeding practices are making sicker dogs." PhD diss., The University of Texas at Austin, 2015: 25.

[22] Pedersen, Niels C., Ashley S. Pooch, and Hongwei Liu. "A genetic assessment of the English bulldog." Canine Genetics and Epidemiology 3, no. 1 (2016): 6.

[23] Swanbeck, Steve. Images of America: The Seeing Eye. Charleston, SC: Arcadia, 2002.

[24] “Blind Man with a Staff and Water-flask, Led by a Dog” (reverse). National Gallery of Art, Samuel H. Kress Collection.

[24.1] Robertson, Patrick. Robertson's Book of Firsts: Who Did What for the First Time. New York: Bloomsbury, 2011.

[24.2] Blindness. 1964-. Washington: 118. 

[25] Cummins, Bryan D. Colonel Richardson's Airedales: The Making of the British War Dog School, 1900-1918. Calgary: Detselig Enterprises, 2003. Also, Ritland, Mike. Trident K9 Warriors. New York: St. Martin's Press, 2013: 143.

[26] Ostermeier, Mark. "History of guide dog use by veterans." Military medicine 175, no. 8 (2010).

[27] Huson, Heather J. "Genetic aspects of performance in working dogs." Chap. 22 in The Genetics of the Dog, eds. Elaine A. Ostrander and Anatoly Ruvinsky, 2nd ed. Cambridge, MA: CABI, 2012. E-book..

[29] Gibbs, Nancy. Animals & Your Health: The Power of Pets to Heal Our Pain, Help Us Cope, and Improve Our Well-being. New York: Time Books, 2016 

[30] Stace, Laura Britton. "Welcoming max: Increasing pediatric provider knowledge of service dogs." Complementary Therapies in Clinical Practice 24 (2016): 57-66