In this lecture we'll discuss domestication of the dog and cat.
By now you should have viewed the video Dogs and More Dogs, which gives us some insight into the domestication of the today's dog from a progenitor species of wolf thousands of years ago. The wolf, Canis lupus, is considered to be the dog's closest relative.
So how did Canis lupus familiaris, today's dog, develop from a species of wolves many years ago? First, let's take a closer look at the terminology we are using to distinguish these animals.
Taxonomical classification is how scientists classify organisms according to the hierarchy you see here. The taxonomy of the dog reflects that he is a member of the animal kingdom, or Animalia. The phylum Chordata, which includes those animals that are chordates or vertebrates, meaning they have a backbone. Dogs are classified in the class Mammalia, so they are mammals. Besides mammals, remember that other classes of chordates include fish, birds, reptiles, and amphibians. Dogs are further classified in the Carnivora order and the Canidae family. The genus Canis and species lupus of the dog are the same as that of the wolf. The dog is then classified as a subspecies, familiaris, of Canis lupus. Now be aware that you will find references that classify dogs as their own species, Canis familiaris, as well as references that classify dogs as they are here, as a subspecies of wolf. This is an ongoing discussion among scientists, so for the purposes of this class we will consider the dog as a subspecies of wolf, but be aware that there is discussion ongoing.
Let's also take a moment to discuss what we mean by domestication. Domestication occurs when the breeding, care, and containment of animals is under the control of humans. Domestication is not a sudden process. It occurs over many generations. And it involves changes in morphology and behavior. Domestication is not the same thing as taming an animal. Taming is making a wild animal more accustomed to humans. But taming involves an individual animal, not a population. It does not result in the long-term development of a new population of genetically distinct animals, as is the case with domestication.
So how were dogs domesticated? The scientific community largely supports what some call the self-domestication theory, in which wolves took advantage of the waste materials being produced from newly forming human civilizations. This implies that the earliest stages of domestication of the dog were probably unintentional and rather involved a significant natural selection component. Natural selection was observed in both behavioral and physical traits.
From a behavioral standpoint, less timid animals would stay at the human civilizations and feed longer, which led to enhanced survival and a gradual increase in the frequency of non-timid behaviors in the population. Also these animals were no longer relying on the pack to survive, so the strict social hierarchies began to relax.
Physical changes reflected a food source that was lower quality than prey (being less energy dense), and so natural selection would favor those animals with smaller body size, and a less robust dentition. And so there developed a new population of animal with these specialized adaptations to live in close proximity to humans.
One key feature of domestication in the dog and other animals is pedomorphosis, the retention of juvenile body morphology and features into maturity. This is sometimes also referred to as neoteny.
So if we look at the modern-day dog, for example, compared to its wolf-like progenitor species we can observe that many of today's dogs are more like a wolf pup than an adult wolf in their behaviors. They're curious, exploratory, playful, and more likely to exhibit subordinate behaviors such as licking and whining.
Physical changes in many of today's breeds also include a smaller body size and a prominent forehead, again, more closely resembling a wolf pup than an adult wolf.
Another effect of domestication is the introduction of new coat colors, as demonstrated by the classic Dmitry Belyaev experiment with silver foxes. The development of new coat colors is thought to be because adrenaline, a hormone involved in stress responses, is on a regulatory pathway that is connected to the production of melanin, a pigment that affects the color of the skin and hair coat.
Today this is propagated through selective breeding, but initially the changes happened without human intention. The phenomenon can be observed in other domesticated mammals as well.
Another effect of domestication is an increased reproductive efficiency. This graphic has cats, who are impacted by this even more so than our dogs. Now in animals such as beef cattle or other production animals, an increase in reproductive efficiency is generally considered to be a good thing. With companion animals, however, it has escalated into a crisis of literally trillions of homeless cats and dogs worldwide, due largely to uncontrolled breeding. Therefore, controlling reproduction is one of the most important responsibilities we have when it comes to our companion animals.
So how exactly is reproductive efficiency increased? Well, compared to a progenitor species, a domesticated animal often has larger litters, is often less selective for a mate, will cycle more frequently, and will often attain sexual maturity at an earlier age.
While we're on the subject of cats, then, let's take a brief look at the taxonomy and domestication of this increasingly popular companion as well.
Like the dog, the taxonomy of the cat reflects that she is a member of kingdom Animalia, and phylum Chordata, the class Mammalia, and order Carnivora. Cats, then, are members of the Felidae family and are classified with the genus and species Felis catus.
The progenitor species of today's companion cat is believed by most scientists to be the African wildcat, Felis silvestris lybica.
As you can see, the cat has not undergone the changes in structure and size that have been observed in the dog. Except for some extreme specific breed characteristics, Felis catus bears close resemblance to Felis silvestris lybica.
So how did cats come to live in close proximity to humans? The earliest signs of domestication were found in ancient Egypt. It is believes the initial cause of domestication likely involved a utilitarian role of cats as predators. There were many rodents in Egyptian granaries, for example, and cats were adept at keeping the rodent numbers in check.
It is also believes that cats held a spiritual significance and were considered a deity in some cultures. They enjoyed several centuries as a protected and adorned species.
In the Middle Ages, however, the cat's place in society underwent a shift, and they began to be scorned by many due to perceived associations with female sensuality and witchcraft. It really is a fascinating history for those of you who wish to look into it further.
Suffice to say, while cats have had a rocky history with humans, fortunately today in the United States we see the cat increasing in popularity as a companion.
