How does domestication work

Over time, some animals become gentler and submit to human instruction -- what's called domestication. In this process, an entire animal species evolves to become naturally accustomed to living among and interacting with humans. It's important to keep in mind that not everyone believes animal domestication is a good thing. This also means that she dislikes the idea of pets in general.

And as an "animal abolitionist," she seeks freedom for all captive animals [source: Lowry ]. However, others look on the history of animal domestication in a kinder light.

The author Stephen Budiansky argues that it is a perfectly natural process that provides advantages to both humans and animals. Budiansky subscribes to the theory that animals actually chose domestication, preferring the reliable comfort of captivity to the harsh wild [source: Budiansky]. He also points out that there are some species that we have, or could have, saved from extinction by domesticating them.

Regardless, no one can deny the enormous contributions that animal domestication has made to the advancement of humankind. Each domesticated species has offered its own spoils and has its own story of domestication, but all domestication happens through roughly the same biological process. Let's take a look at this process. How do humans orchestrate an entire species' transformation from wild to mild? 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 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. 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. Several domesticated species have followed this path, among which are dog Canis familiaris , cat Felis catus , or chicken Gallus domesticus [ 29 ]. In the prey pathway, humans have initiated domestication, perhaps as a response to depletion of local stocks of prey animals that humans had hunted for thousands of years [ 31 ], to enhance the yield or predictability of a resource meat or hides [ 29 ].

Over time and under certain circumstances, these game management strategies developed into actual herd management and, eventually, the controlled breeding of managed animals [ 28 ]. The main species that followed this pathway are sheep Ovis aries , goat Capra hircus , or cattle Bos taurus [ 29 ]. In the direct pathway, humans deliberately set out to domesticate a species [ 28 , 31 ]. This pathway skips the early phases of habituation and management and starts with the capture of wild animals with the deliberate intention of controlling their reproduction [ 29 ].

This pathway occurred more rapidly and was accompanied by a dramatic bottleneck [ 29 ]. The main species are horse Equus caballus , donkey Equus asinus , and dromedary Camelus dromedarius [ 28 ]. Species that followed either commensal or prey pathways tend to possess more traits that make them appropriate candidates for domestication. Conversely, species on directed pathways likely possess barriers to domestication that require more knowledge on the part of humans to overcome [ 28 , 31 ].

Whatever the pathway followed, captive animals began to be domesticated at some point. Yet, as for domestication, there is no consensus today about what a domesticated species is see [ 27 ] for a review of the main definitions.

Nevertheless, most authors considered that a domesticated species is a group of animals reproduced in captivity and modified from their wild congeners [ 27 ]. In other words, there is not a clear biological separation between wild and domesticated animals [ 33 ]. In addition, a domesticated animal is neither in a final nor a static status, and thus farmed species are still evolving today, particularly in response to changes in technology and husbandry practices, which themselves are evolving and constantly improving [ 34 ].

Conversely, domesticated species can sometimes return to nature, a process known as feralization [ 35 ]. During domestication, five main genetic processes were involved [ 15 , 28 , 34 ], including inbreeding and genetic drift two uncontrolled processes , natural selection in captivity and relaxation of natural selection two partially controlled processes , and active selection one controlled process [ 34 , 35 ].

The two uncontrolled processes are due to the limited size of the population known as inbreeding and the random changes in gene frequencies genetic drift. The two partially controlled processes are natural selection in captivity that accounts for selection imposed on captive populations that cannot be attributed to active or artificial selection and relaxation of natural selection expectably accompanying the transition from wild to captive environments [ 35 ].

At last, the fifth genetic process is controlled, known as active selection, because changes are directional [ 34 , 35 ]. Domesticated animals have been profoundly modified during domestication. Indeed, the variation range of certain traits within a domesticated species occasionally exceeds that in whole families or even orders [ 36 , 37 ]. Modifications resulting from domestication concern morphoanatomy, physiology, behavior, and genetics [ 31 , 35 , 38 , 39 , 40 ].

Behavior is probably the first to have been modified during domestication [ 35 ]. Nevertheless, behavioral traits neither appeared nor disappeared during domestication but rather are the response thresholds that changed [ 34 , 35 ]. One of the most remarkable behavioral changes shared by all domesticates is their tolerance of proximity to or complete lack of fear of people [ 31 , 37 , 39 ].

Besides, because humans provide shelter, food, and protection against predators, domesticated animals most often express a lower incidence of antipredator behaviors and show lower motivation for foraging [ 34 ].

More generally, mood, emotion, agnostic and affiliative behavior, as well as social communication all have been modified in some way by domestication [ 39 ]. Most domesticated animals are also more precocious than their wild counterparts [ 34 ]. The activity of their reproductive system became enhanced and relatively uncoupled from the environmental photoperiod, and they all acquired the capacity to reproduce in any season and more often than once a year [ 37 ].

At last, the most spectacular and obvious changes concern morphology, among which are the animal size dwarfs and giants , proportions fewer vertebrae, shorter tails , color, length and texture of coat, wavy or curly hair, rolled tails, and floppy ears or other manifestations of neoteny the retention of juvenile features into sexual maturity [ 37 , 39 ]. In most domesticated species, head or brain size has decreased [ 34 ].

The most illustrative example of such considerable changes is the morphological variations in dogs [ 37 ]. At the beginning of the twentieth century, modern breeding programs were initiated, leading to dramatic changes in productivity, e. Even though the decision to consider farmed or captive animals as domesticated is subjective and arbitrary [ 35 , 41 ], most authors agree that about 40 species around the world that directly or indirectly contribute to agriculture are domesticated; this number varies between 20 and 50 following the definitions used for a domesticated animal [ 36 , 42 , 43 , 44 ].

Several of those domesticated species have a distinct scientific name than their wild ancestors [ 25 ]. For the five most valuable species, the domestication resulted in the creation of hundreds of breeds, particularly in the past centuries [ 42 , 45 , 46 ]. In France, the article D. Breeds have therefore both a biological sense common features and a social acceptance group of breeders ; the relative importance of the latter increased in the past years, for scientists as well as in the application of policies [ 47 ].

The wild ancestor of cattle is a group of races of the now extinct aurochs Bos primigenius [ 48 , 49 , 50 ]. The aurochs, the last specimen of which died in a Polish park in , had a very wide geographic distribution, which extended from East Asia to Europe and North Africa [ 42 , 48 , 50 ].

Traditionally, two major types of domestic cattle are considered: zebu Bos indicus which have a prominent thoracic hump and taurine Bos taurus , which do not [ 40 , 42 , 49 , 50 ]. However, these two species fully interbreed, and a meta-analysis of different microsatellite datasets revealed taurine-zebu admixture over Europe, southwest Asia, and Africa [ 40 , 45 , 49 , 50 ]. Molecular evidence suggest that these two species came from two independent domestication events: zebu cattle were domesticated in the Indus valley region ca.

However, Larson and Burger [ 29 ] recently suggested that only the latter was domesticated, while zebu may have resulted from the introgression of wild zebu populations into taurine cattle that were transported eastward. During several millennia, extensive gene flow among different groups of domestic cattle, as well as with aurochs until its extinction, was possible, leading to relatively high effective population sizes and preventing genetic drift at the regional scale [ 40 , 48 , 50 , 51 ].

This might partly explain the relatively large cattle gene pool despite a likely bottleneck at the time of domestication [ 50 ]. Besides, it is also possible that other species were crossed with cattle in some areas of the world, including the yak Bos grunniens in Nepal or banteng Bos javanicus in Southeast Asia and Indonesia, which also contribute to maintain or increase genetic variability [ 40 ].

The large size of cattle and its low growth, as well as the early use for milk or traction, imply relatively low levels of directed selection during millennia [ 51 ]. However, this situation changed dramatically about years ago with the emergence of breed concept [ 50 ]. The first cattle herd book was published in Britain in [ 49 ]. Since that time, stronger selection pressures have been applied to local populations followed by standardization of the desired conformation and performance, such as high milk yield for dairy cattle breeding programs [ 49 ].

This led to an isolation of breeds from each other ca. Nevertheless, gene flow between neighboring regions did not completely stop, as deliberate upgrading was realized in order to increase production characteristics by using bulls of other populations from the same or a different country [ 45 ].

More recently, the number of males involved in reproduction schemes has drastically decreased with the expansion of artificial insemination, leading to another strong reduction of effective population size of breeds and inexorably to a genetic drift and loss of alleles [ 46 , 50 , 63 ].

For example, at the worldwide level, the Holstein cattle has an effective population size of about 50 [ 50 ]. This strong decrease of the effective population size might explain the strong reduction in fertility as well as the genetic diseases observed in this breed [ 50 ]. An even more extreme result was found in Japan, where the Japanese black cattle had an effective population size of People in the global wildlife trade will make the claim that any number of animals, from elephants to reptiles to parrots, are domesticated because they can live alongside humans.

The difference is that these animals are captured from the wild or have been bred for just a handful of generations. This is not domestication and never will be. Wild animals belong in the wild, not living alongside humans like their domesticated counterparts. Humans have successfully adapted a number of animals to live alongside us , including cats, dogs, cattle, pigs, donkeys, horses, and chickens. However, domestication is a process that takes thousands of years.

Those animals are wild, abused into submission, and should not live alongside humans in the same way as domesticated animals. What is Domestication? An estimated timeline of animal domestication Saey, Tina Hesman. Domestication happened at different points in all corners of the world, but animals were all domesticated for a reason, even if that is not their purpose now. Dogs were domesticated to assist in hunting, oxen to pull heavy loads, and farm animals like cows, horses, goats, and sheep for food and milk.

While some roles are the same, dogs are no longer primarily used for hunting, horses developed into a means of transportation, and goats have recently been used to eat unwanted plants! Dogs were domesticated from wolves by selecting the wolf pups that were likely the least aggressive, most obedient, had smaller jaws, or a certain coloring depending on the culture that was domesticating them.

This select breading has created the entirely new species of dog, separate from wolf. Domestication also affects the animals brought into human life. Archeologists can usually tell if certain animals are domesticated based on their bones Domesticated horses and cattle used to pull heavily loads for farm work often have osteoarthritis or leg strain that would not be there otherwise.

Animal domestication changed a great deal of human society.