Top Signs of Animal Domestication

How Can Archaeologists Tell if an Animal is Domesticated?

The domestication of animals was an important step in our human civilization, involving the development of a two-way partnership between humans and animals. The essential mechanisms of that domestication process are a farmer selecting for an animal's behavior and body shape to suit his or her specific needs, and an animal which thus requires care survives and thrives only if the farmer adapts his or her own behaviors to take care of them.

The process of domestication is a slow one—it can take thousands of years— and sometimes archaeologists have a difficult time identifying whether a group of animal bones in a particular archaeological site represents domesticated animals or not. Here is a list of some of the signs that archaeologists look for in determining whether the animals in evidence at an archaeological site were domesticated, or merely hunted and consumed for dinner.

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Body Morphology

European domestic pigs, descendants of the European wild boar.
European domestic pigs, descendants of the European wild boar. Jeff Veitch, Durham University.

One indication that a particular group of animals might be domesticated is a difference in body size and shape (called morphology) between a domestic population and animals found in the wild. The theory is that over a few generations of keeping animals, average body size changes because the farmers deliberately select for certain desirable characteristics. For example, the farmer might consciously or unconsciously select for smaller animals, by killing the larger unruly ones before they have a chance to breed, or by keeping the ones that mature earlier.

However, it doesn't always work that way. Domestic llamas, for example, have bigger feet than their wild cousins, one theory being that poorer diet leads to malformation of the foot. Other morphological changes identified by archaeologists include cattle and sheep losing their horns, and pigs trading muscles for fat and smaller teeth.

And in some cases, specific traits are purposefully developed and maintained in an animal population, resulting in different breeds of animals such as cattle, horses, sheep or dogs.

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Population Demography

Domestic Cow (Bos taurus) in Rural Zurich, Switzerland
Domestic Cow (Bos taurus) in Rural Zurich, Switzerland. Joi Ito

Describing the population of a an archaeological assemblage of animal bones, by building and examining a mortality profile of the demographic spread of the animals represented, is another way that archaeologists identify the effects of domestication. A mortality profile is created by counting the frequency of male and female animals, and the age of animals when they died. The age of an animal might be determined from evidence such as length of the long bones or wear on teeth, and the sex of an animal from size or structural differences.

Then a mortality table is constructed showing the distribution of how many females versus males there are in the assemblage, and how many old animals versus young.

Why Are Mortality Tables Different?

Bone assemblages that are the result of hunting of wild animals generally include the weakest individuals in a herd, since the youngest, oldest or sickest animals are the ones most easily killed in a hunting situation. But in domestic situations, juvenile animals are more likely to survive to maturity—so you might expect fewer juveniles to be represented in an assemblage of domesticated animal bones than those hunted as prey.

The mortality profile of an animal population may also reveal culling patterns. One strategy used in herding cattle is to keep the females into maturity, so that you can get milk and future generations of cows. At the same time, the farmer might kill all but a few of the males for food, those few kept for breeding purposes. In that kind of animal bone assemblage, you would expect to find the bones of juvenile males but no or much fewer juvenile females.

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Site Assemblages

Artifacts from domesticated horses would include shoes, nails, and hammers.
Artifacts from domesticated horses would include shoes, nails, and hammers. Michael Bradley / Getty Images

Site assemblages—the content and layout of archaeological sites—can also hold clues to the presence of domesticated animals. For example, the presence of buildings associated with animals, such as pens or stalls or sheds, is an indicator of some level of animal control. A pen or stall might be identified as a separate structure or separate part of a residence with evidence for animal dung deposits.

Artifacts such as knives for shearing wool or bits and bit guards for horses have been found at sites and interpreted as evidence for domestication.

Saddles, yokes, leashes, and hobbles are also strong circumstantial evidence for the use of domesticated animals. Another form of artifact used as evidence for domestication is art work: figurines and drawings of people on horseback or oxen pulling a cart. 

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Animal Burials

4,000-Year-Old Pig Skeleton at Taosi
The remains of a 4,000-year-old pig found at the Chinese archaeological site of Taosi. The descendants of this domestic pig are now found all over the world. Image courtesy of Jing Yuan

How the remains of an animal are placed within an archaeological site may have implications about the animal's status as a domesticate. Faunal remains are found on archaeological sites in many different forms. They may be found in heaps of bone, in a rubbish heap or midden with other forms of refuse, scattered haphazardly around the site, or within a purposeful burial. They may be found articulated (that is, the bones still laid out as they were in life) or as separate pieces or tiny fragments from butchering or other cause.

An animal such as a dog, cat, horse or bird who has been a valuable member of a community may be buried alongside humans, in a cemetery for animals or with its owner. Dog and cat burials are known in many cultures. Horse burials are common in several cultures such as the Scythians, the Han Dynasty of China or Iron Age Britain. Mummies of cats and birds have been found in ancient Egyptian contexts.

In addition, large multiple deposits of bones of a single type of animal might suggest tending of large numbers of animals and thus imply domestication. The presence of fetal or newborn animal bones may also suggest that the animals were being tended since these kinds of bones rarely survive without purposeful burial.

Whether an animal has been butchered or not may have less to do with whether it was domesticated; but how the remains were treated afterward may suggest some form of care taken place before and then after life. 

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Animal Diets

Chickens feed at a poultry wholesale market in Chengdu of Sichuan Province, China
Chickens feed at a poultry wholesale market in Chengdu of Sichuan Province, China. China Photos / Getty Images

One of the first things an animal owner has to figure out is what to feed her livestock. Whether sheep are pastured in a field, or a dog fed from table scraps, the diets of a domesticated animal are almost always radically changed. Archaeological evidence of this shift in diet may be identified by wear on teeth, and changes in body mass or structure.

Stable isotope analysis of the chemical makeup of ancient bones has also greatly assisted in the identification of diets in animals.

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Mammalian Domestication Syndrome

Why is This Dog So Cute?
Why is This Dog So Cute? This is Helios, an approximately 3-year-old cattle dog/greyhound mix with Lucky Dog Animal Rescue. Lucky Dog Animal Rescue

Some studies suggest that the entire suite of behaviors and physical modifications developed in domesticated animals—and not just the ones we can spot archaeologically—might very well have been created by genetic modifications of a stem cell connected to the central nervous system.

In 1868, the pioneer evolutionary scientist Charles Darwin noted that domesticated mammals each exhibited a similar set of physical and behavioral traits not seen in wild mammals—and, most surprisingly, those traits were consistent across several species. Other scientists have followed in Darwin's footsteps in adding traits specifically associated with domestic animals.

Traits of Domestication

The suite of traits known today, which American evolutionary biologist Adam Wilkins and colleagues call the "domestication syndrome," includes:

  • increased tameness
  • coat color changes including white spots on faces and torsos
  • reductions in tooth size
  • changes in the shape of the face, including shorter snouts and smaller jaws
  • curly tails and floppy ears—out of all the wild versions of domestic animals, only the elephant started out with floppy ears
  • more frequent estrus cycles
  • longer periods as juveniles
  • reductions in total brain size and complexity

Domestic mammals which share parts of this suite include guinea pig, dog, cat, ferret, fox, pig, reindeer, sheep, goat, cattle, horse, camel, and alpaca, among many others.

Without a doubt, the people who began the domestication process, some 30,000 or more years ago in the case of dogs, clearly focused on the reduction in fearful or aggressive responses to humans—the famous fight or flight response. The other traits don't seem to have been intended, or even good choices: wouldn't you think hunters would want a smarter dog or farmers a pig that grows up quickly? And who cares about floppy ears or curly tails? But the reduction in fearful or aggressive behavior has been found to be a prerequisite for animals to breed in captivity, let alone live close to us comfortably. That reduction is tied to a physiological change: smaller adrenal glands, which play a central role in the fear and stress responses of all animals.

Why These Traits?

Scientists have been struggling to find the single cause or even multiple causes for this set of domestication traits since the mid-19th century of Darwin's "Origin of Species." Possible explanations for the suite of domestication traits suggested over the last century and a half include:

  • gentler conditions of living, including improved diets (Darwin)
  • reduced stress levels (Russian geneticist Dmitry Belyaev)
  • hybridization of species (Darwin)
  • selective breeding (Belyaev)
  • selection for "cuteness" (German ethologist Konrad Lorenz)
  • changes in the thyroid gland (Canadian zoologist Susan J. Crockford)
  • most recently, changes in neural crest cells (Wilkins and colleagues)

In a 2014 article in the scientific journal Genetics, Wilkins and colleagues point out that all of these traits have something in common: they are linked to neural crest cells (abbreviated NCCs). NCCs are a class of stem cells that control the development of tissues adjacent to the central nervous system (along the spine) during the embryonic stage, including face shape, ear floppiness, and size and complexity of the brain.

The concept is somewhat debated: Venezuelan evolutionary biologist Marcelo R. Sánchez-Villagra and colleagues recently pointed out that only canids show a large percentage of these features. But the research continues.

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A Few Recent Studies

Reconstructed farm with nine houses of a large-scale farmer from the Viking Age, Viking Center Fyrkat, Fyrkat, Hobro, Denmark, Europe
Reconstructed farm with nine houses of a large-scale farmer from the Viking Age, Viking Center Fyrkat, Fyrkat, Hobro, Denmark, Europe. Olaf Krüger / Getty Images