Juliana Damasceno and Rachel Stopatto Righetti, 2013
The domestic dog (Canis familiaris) that we currently know is the species among the thirty-eight belonging to the family Canidae that has been fully domesticated and has been our companion far longer than our other favorite pet, the cat. Fossil evidence shows that since the Paleolithic age, dogs have been linked to humans. This mutual relation caused the selection of the ancestral Canis lupus (wolf) to occur artificially because of the wolf‘s proximity to man and because of some of the wolf‘s useful characteristics (hunting, guarding farm animals, companionship, etc.). Despite the great variety of breeds that morphologically diverge, the health, biological and psychological needs of dogs are common to all breeds, emphasizing one or another characteristic for each breed. Pet dogs generally live in restricted environments with their owners, who must ensure that their physical and psychological needs are satisfied. Thus the welfare of the animal depends on humans‘ knowledge of the behavior of the species. An understanding of dog behavior and the right tools can provide better care for these animals (environmental enrichment techniques), and various diseases can be avoided.
The current population of dogs in the United States is approximately 70 million, according to the Animal Veterinary Medical Association (AVMA), and in the United Kingdom 23% of all families have a dog, which is equivalent to 8 million dogs, according to the Pet Food Manufacturers‘ Association (PFMA). In addition to being one of our most important pets, dogs are also used as study models in various veterinary, odontology, medical, neuroscientific, behavioral and other studies. To ensure these animals‘ physical and psychological health independent of their environment, it is important to understand their evolution, domestication and typical behavior. With understanding and the right tools, it is easy to provide satisfactory and effective conditions for dogs‘ health and welfare. This chapter provides a general overview of dogs‘ history from their origins and their proximity to man until today, highlighting the breadth and necessity of these animals‘ behaviors and indicating some tools to ensure a more complex and psychologically healthy canine life.
History and Domestication
The Canidae family, which includes the dog (Canis familiaris), began its divergence from the other carnivorous families approximately 50 million years ago. The canids are now represented by thirty-eight species living around the world except for Antarctica and some oceanic islands. Of the pets we now know, the dog was the first to be domesticated. The domestication of the dog occurred even before humans developed a closer contact with production animals and thousands of years before the domestication of our also beloved pet, the cat. Archaeological evidence shows that the domestication of the dog began during the Glacial Era, when human subsistence still depended on hunting, gathering and foraging.
Davis and Valla (1978) reported on a human fossil found in Israel dated between 10.000-12.000 years ago that was buried with a Canidae puppy, which could have been a domesticated wolf or even a “dog”. The human belonged to the Natufians, an Egyptian culture from the Epipaleolitic period. The Natufian culture comprised hunters and gatherers about to become farmers. The genre of the buried human could not be identified because of its bent position and because it was on its side although the puppy‘s age was estimated at approximately four or five months at time of death. The human skeleton had its hand on the puppy‘s chest, demonstrating a strong connection between them, and there has been a special human-dog relationship since that time. Valla (1990) reports on another fossil registration, also found in Israel and belonging to the same Natufian culture, of a human buried beside two Canidae that were perhaps dogs. These and other archaeological sites that had canidae skeletons next to humans confirm that beyond domestication, a close relation between humans and dogs has existed for thousands of years.
Despite clear evidence that dogs have been among us since long ago, several questions emerge when we think about the dog‘s ancestors and origins. The most accepted and widespread theory, based on the most evidence, is that the dog comes from the domestication of wolves (Canis lupus). Although this theory is the most accepted, there are few details regarding how the first dog appeared or how such a variety of breeds developed. Other less clear and more uncertain theories and studies regarding the origins of dogs have been presented such as theories involving the jackal and the coyote as possible ancestors. However, facts to support these theories are even more scarce than support of the wolf ancestor theory.
The most accepted theory and the one that has the most genetic and morphologic evidence infers that the modern dog began its differentiation from wolves more than 100 thousand years ago. The existence of isoenzymatic alleles, polymorphic microsatellites and mitochondrial DNA sequences, which dogs and wolves have in common,, confirm the closeness between them. A series of studies regarding aspects of behavior, vocalization, morphology and molecular biology indicate that the main and perhaps the only ancestor of the dog is the wolf.
If dogs did indeed descend from wolves, how did domestication occur with such wild animals? Domestication is a principle of evolution, a synonym for change, combining genetic changes from one generation to the next as well as change induced by the environment. Evolution affects animals in three main manners: psychologically, morphologically and behaviorally. The process of domestication is strongly allied with and influenced by human actions both culturally and biologically. The cultural aspects are related to the incorporation of animals in society; animals are perceived as property to serve humans. The biological aspects are related to the process of evolution, from an animal‘s wild origins to a friendly and docile relationship with humans.
According to the literature, wolf domestication began in the Mesolithic period, when humans were still nomadic hunters. Those wolves that felt the least afraid of men started to follow and help them, first as guards to scare away a possible enemy, either human or animal, and then actively participating in the hunt, collaborating with humans to search and attack prey.
There are several theories regarding wolves‘ proximity to man. One theory states that when wolves were killed so that their skins could be used for clothing, their puppies, instead of also being killed, were raised by man, becoming more meek and less aggressive. In this manner, wolves were progressively tamed. Another theory suggests that when wolves helped hunt, the just-born puppies remained in the caves, creating human proximity and establishing a closer relation. Wolves became progressively closer to man and less aggressive. As a result of such proximity, increased food sources, and greater safety, the wolves‘ reproductive rate increased. Over time, as humans became more sessile and focused on the land, animals gradually became genetically different from their ancestors, adapting to human activities and modifying their morphology and behavior.
Driscoll et al. (2009) state that domesticating animals and plants has allowed human to accumulate more resources and enjoy better nutrition, which caused the Neolithic revolution to occur, bringing not only an agricultural economy but the development of “urban” life. Neolithic farmers were the first geneticists, selecting domestic animals and plants for their use and developing such characteristics as a more docile temperament, increased jaw and neck strength, and great speed among other characteristics somehow selected by man that began what we know as artificial selection.
The evolution of domesticated species is directly related to artificial selection whereas natural selection has a secondary place in this process. Artificial selection, as the name suggests, is the opposite of natural selection and is related to human actions, economic requirements, aesthetic desires and cultural requirements. In artificial selection, crossings occur by human interference and may occur during the pre-zygotic stage (when mates are chosen by man) or post- zygotic stage (when the most suitable progeny reproduce differently). In his book Domestication, Roots (2007) states that genotype modifications, facing artificial selection, interrupt naturally established systems, causing changes in some processes such as the genotype removal of recessive alleles. These and other genetic manipulations may cause a loss of diversity or what we now know as genetic erosion, making individuals more susceptible to diseases. Driscoll et al. (2009) infer that artificial selection may occur in two different intensities: “weak” or “strong”. “Weak”artificial selection occurs in the post-zygotic stage, whereas “strong” artificial selection may occur in either the pre- or post- zygotic stage, for example, breeding good dairy cow offspring from good females.
Contrary to artificial selection, which is connected to changes caused by humans, natural selection is related to environmental mechanisms in which characteristics that may represent an advantage are passed from generation to generation by the reproductive success of individuals who carry these characteristics. This reproductive success is linked to sexual selection and the intraspecific competition for mates.
During the process of domestication, natural selection most likely favored animals that had characteristics more amenable to coexisting near humans; for example, animals that were more docile and helped humans in hunting and protected them received resources supplied by humans such as protection and food.
The artificial selection that was utilized by humans caused changes in several original aspects of dogs (previously wolves), especially in their morphology. Body and head sizes were reduced by the domestication process in dogs as well as in many other species of mammals. Although dogs have become closer to man and have been domesticated for thousands of years, the phenotypic variation of the dog we know today is more recent, from approximately 3.000 to 4.000 years ago.
The morphology of the current dog, a pet, has diverged in size as well as shape. Thus many types of dogs have developed with variations in hair color and length, size, eye color, behavior and temperament. Within this huge variety, currently there are approximately 400 species of dogs, ranging from a little Pinscher to an immense Weimaraner. Some breeds shed less hair and are smaller so that they can be housed in an apartment or small house; some breeds are more docile, some are more or less active, some are better for children or for home and job safety, some are bred to be champions in beauty contests or competitions, etc. More breeds have been developed through the years, either inside laboratories with DNA manipulation or by crossing breeds, always aiming to satisfy humans‘ vanity and consumerism.
In addition to this manipulation in developing breeds, modifying genetics, morphology and animal characteristics, this process may also lead to several pathological and behavioral problems.