How Animal Domestication Works

How could wild creatures like wolves be ancestors of cute little Pomeranians? To understand, we first need to know how genetics and evolution work. Animal offspring inherit genes from their parents, and these genes indicate what traits the offspring will have. The variety of genes and the possibility of mutation allow for animal species to change, or evolve, over time. In the process of natural selection, the animals with traits that allow them to survive better will be more likely to breed, until very gradually the only members who survive end up inheriting those helpful traits.

In artificial selection, humans choose desirable traits in animals that they want to see in the animal's offspring. For example, if people want bigger horses to pull their loads, they can put the biggest male and the biggest female horses together and encourage them to breed. This increases the chances that the offspring will also be big. Using another big horse to breed with that offspring will continue the process, until finally, after generations of people continue the process on generations of horses, the entire horse species will be bigger. Using the same process, humans can breed animals to be a certain color, furrier, smaller, gentler or stronger, among other things. This is how humans domesticate animals -- so much so that wolves eventually become a different animal, gentle enough to keep in the home. Or, sheep yield more wool. Or, horses let us ride them.

If this is true, then why don't we ever see a pet panda or someone riding a zebra? It turns out that we can't domesticate every animal. Author Jared Diamond writes that humans have succeeded in truly domesticating only 14 animal species out of about 148 candidates [source: Diamond]. He proposes that for humans to domesticate an animal species, the species usually satisfies these criteria:

Pandas and zebras are far too violent and have thwarted human attempts to domesticate them. However, exceptions might come to mind after examining Diamond's list. For instance, isn't the wolf (as predecessor to the dog) vicious and the cat solitary? The stories of dogs and cats are unique ones that we'll learn about a little later.

On the next page, we'll take a look at the long story behind domestication.

Some of our earliest evidence of man (and art) is tied to animals. Cave illustrations depict bison and deer. Obviously, animals have played a large part in the lives of humans throughout our history, becoming integral to our survival, our history and our very identity. It seems natural that we would want to incorporate and include animals in our lives as much as possible for food, companionship, clothing, milk and a slew of other things.

From archeological evidence such as fossils, historians have learned a lot about man's domestication of animals. Animal domestication is partly tied to human domestication, or the human shift from hunter-gatherer to farmer. Though hunter-gatherers worked with domesticated dogs long before human domestication, later on, farmers saw the benefit of keeping livestock. As some people became farmers and started to settle in one place, raising domesticated livestock offered them the convenience of fresh meat as well as manure for fertilizing crops. Diamond points out that the civilizations that domesticated animals (and plants) consequently wielded more power and were able to spread their cultures and languages [source: Diamond].

Civilizations all over the ancient world domesticated animals for various reasons, depending on which animals were around them and what the animals could provide humans. Certain animals even took on religious significance in many civilizations, such as Ancient Egypt and Rome. Here is a breakdown of where animals were originally domesticated:

From what experts have learned about the progress of animal domestication, as a species becomes more domesticated, it changes. For example, domesticated animals' brains may become smaller and their sensory abilities less precise [source: Diamond]. Presumably, these changes occur because the animal doesn't need the same level of intelligence and sharp senses of sight and hearing for survival in a domesticated home. Other common changes include floppy ears, curly hair and especially changes in size and mating habits. Domesticated animals are more likely to mate year-round, rather than seasonally, as they do in the wild [source: Encyclopedia Britannica]. These changes and others often cause domesticated animals to look drastically different from their wild ancestors.

Humans themselves have changed significantly as a result of animal domestication. For example, milk has changed our digestive system. Before animal domestication, people naturally developed lactose intolerance as they grew into adulthood (and no longer needed a mother's breast milk). That is not always the case anymore. When humans started raising livestock, they started drinking more milk, and this has adapted our digestive systems to accommodate milk throughout our lives.

Next, we'll learn how the legendary evolution of the dog may have produced man's earliest and most faithful animal companion.

How a wolf could transform from suspicious, wild beast to obedient, cuddly Fido may seem mystifying or even unbelievable. But scientists have used DNA evidence to show that, more than likely, the dog did indeed descend from the gray wolf.

Although the oldest fossils of a domesticated dog are from a 14,000-year-old dog grave, DNA evidence suggests dogs diverged from wolves much earlier than that (with estimates ranging from 15,000 to more than 100,000 years ago) [source: Wade]. Regardless, historians agree that humans domesticated dogs before any other animal -- making dog man's oldest friend, if not his best.

Scientists can only guess how dogs and humans first became friendly. A popular theory suggests that humans began taking in wolf pups and eventually were able to tame them. Another theory proposes that the tamest wolves were not afraid to rummage through human trash sites to find food. Because they fed this way, these tamer wolves were more likely to survive and evolved into dogs through natural selection [source: NOVA].

Because wolves operate in packs, humans easily took the place of the "highest ranking wolf." So the animals quickly learned obedience. As tamer wolves were more likely to stick around humans, evolution naturally (or humans intentionally) bred tamer and tamer wolves, until eventually, we got the dog. Sometime during this process, man and tamed wolf realized they made for a dynamic duo on the hunting scene. A combination of human ingenuity and wolf speed and ferocity, this pair shared the rewards of their captured game in a mutually beneficial relationship.

However, this evolution of wolf to dog still begs the question: Why do dogs look and act so much different from wolves? A 20th century Russian Geneticist, Dmitri Belyaev, was able to solve part of the mystery surrounding how a wolf made such a drastic transformation. In his attempts to breed tame foxes, Belyaev found that after several generations of selective breeding, foxes not only became tamer (which he expected) but also began to take on dog-like characteristics.

Though DNA evidence tells us that wolves, not foxes, are the forefathers of dogs, this experiment uncovered surprising revelations about how behavior and appearance could have changed wolves into dogs [source: NOVA]. As the foxes became tamer, so also did they develop floppy ears, short snouts, spotted coats, highly-set tails and even a tendency to bark. Amazingly, many of these characteristics are absent in wild foxes, much as they are in wolves, so neither artificial nor natural selection could intentionally draw them out. Instead, genes that account for tameness must also carry a code for such things as floppy ears.

Belyaev's findings also help us understand how different dog breeds ended up looking so different from each other when wolves look relatively uniform. Tameness brought about variation unseen in wild wolves, and humans embraced this variation. Smaller cuddly dogs are better at keeping your lap warm, while bigger, faster dogs are better at hunting. Instead of choosing one or the other, humans bred different dogs for different purposes. In the 19th century we saw a surge in the number of dog breeds along with the advent of dog shows.

Now that we have learned about the domestication of dogs, we'll find out how cats clawed their way into our hearts and homes.

In sharp contrast to dogs, cats did not evolve to look or act very different from their wild ancestors. This fact has made it difficult for scientists to determine when exactly cats domesticated. Although evidence shows that cats probably did not evolve from modern large cats, such as lions and tigers, Archaeologists cannot use the shapes of old bones and scientists cannot investigate DNA to distinguish between ancient small wild cats and modern domesticated cats. However, some evidence does lead scientists to believe that the modern domestic cat (Felus catus) may have descended from a European wild cat (Felis silvestris) and an African wild cat (Felis lybica), cats that still exist in the wild.

Other clues provide some convincing evidence about early feline domestication. For example, excavation of a 9,500-year-old gravesite revealed the remains of a human buried alongside a cat. From this evidence, historians believe that most likely by this time humans got personally attached to their feline friends. The proximity of the human and cat indicates that the burial was intentional and that cats held a significant role in that culture.

Even if guessing when cats became domesticated is difficult, why humans took them in is a little easier to speculate. Every kid who's seen a "Tom & Jerry" cartoon is familiar with cats' infamous dislike of mice. Usually cats are more successful at capturing, or at least scaring, their rodent prey than Tom ever was. It's exactly this skill that probably made cats so appealing to humans. Trading pest-control for food and shelter, cats eventually overcame their aversion to domestication.

Cats probably did not take to domestication as easily as wolves/dogs did because cats have no social hierarchy that allows humans to take the alpha role. Wolves travel in packs, following a highest-ranking wolf, but a cat is a solitary and proud animal who takes orders from no one. Although the domestic cat is its own species, its independence and the fact that domestication didn't cause any drastic changes allowed feral cats to survive on their own fairly well even if raised in the luxury of a human home. So, although they are not known for taking orders from humans, perhaps cats stick around because they enjoy receiving food and shelter from their human masters (or servants, depending on who you ask).

Although it was nice to have hunting and pest control partners, humans needed to rely on more than just dogs and cats to advance their civilization. Next, we'll find out how other domesticated animals helped humans progress into transportation and farming.

At first, it was obvious that livestock offered early farmers a handy supply of fresh meat and milk. Eventually, people discovered that animals could also assist with farming, and provide fertilizer and new clothing material. Here's a list of some of the major livestock animals that have played significant roles in the history of humanity:

Next, we'll take a look at many other animals that provided what was perhaps just as important -- transportation for long distances and heavy loads.

Before the invention of the steam engine, the automobile, and the airplane, there was the horse-drawn carriage. And although this may seem primitive in comparison to modern transportation, keep in mind that animals allowed for some of the greatest advancements of civilization for millennia through migration and trade. Here are some of the most significant animals that allowed for human transportation:

Although livestock and transportation animals provided much-needed labor and helped humans forge civilization, we shouldn't forget about little guys. Next, we'll learn how certain rodents, insects and other animals offered their own contributions through domestication.

People have been able to domesticate a variety of other animals that provide numerous other functions for us. These include:

Some of the animals included in the previous list arguably aren't "domesticated" at all. Authorities in the subject, such as Jared Diamond, use a strict definition of domestication, which only includes animals whose genetic makeup has changed from their ancestors so to allow humans to manipulate their breeding and diet. We can still tame individual animals to do what we need them to do without altering their inheritable nature. For instance, even though Hannibal famously crossed the Alps on elephants, Diamond argues that elephants can only be called tamed because they never formed a whole new species through the domestication process.