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The Animal Connection: Why Do We Keep Pets?

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Pets are popular family members. / iStock image.

Ed. Note: Another favorite this Friday about those furry members of our family—no, not your Grandpa Ed, but your pet. This post was selected as an Editor’s Selection on It has been slightly modified from it’s original posting.

I’ll never forget the day S brought home a live chicken. When we lived in Queens, there were a number of fresh poultry and livestock suppliers that catered to the growing West Indian community so live poultry was readily available, but there were also a few backyard farmers in the neighborhood. S was at a gas station when he heard a cheeping noise. He knelt down to investigate and when he straightened up, found a chick sitting on the mat in the car. “What was I supposed to do?” he asked showing me the chick later that day. “It jumped in the car.”

His affinity with animals is nothing new. He trained goldfish. He has refused to kill mice, insisting on releasing them into the wild. At fifteen, he nursed a pigeon back to health after setting its broken wing. During a trip to Trinidad, he befriended a bull—despite being warned away by my uncles—by sitting in the mud with it for hours. And today, we are the proud parents of two cats (we did not keep Chicken Little) who can’t seem to get enough of him. I am definitely second fiddle in their feline minds—though handy to have around when they need to be fed.

S is not alone. Pat Shipman (2010) notes the significance of pets—and animals—in our lives:

In both the United States and Australia, 63% of households include pets, compared to 43% of British and 20% of Japanese households. In the United States, the proportion of households with pets is larger than those with children (522).

This relationship, dubbed the animal connection by Shipman, may have played an important role in human evolution, linking the traits that distinguish Homo sapiens from other mammals. How is it that some animals transitioned from food to friends, and what is the significance of this relationship?

The animal connection is the process by which pets or livestock become companions and/or partners, and are treated as members of the family. It refers to the close relationship between animals and humans starting 2.6 million years ago (mya), beginning with the use and study of animals by humans, and leading to regular social interactions. Today this is manifested in the adoption of animals and the care provided to them in the course of that relationship. The roots of this relationship may be found in the development of three often recognized traits of humans: making and using tools, symbolic behavior (including language, adornment, and rituals), and domestication of other species. Shipman views the animal connection as a fourth trait, tying the other three together and having an immense effect on human evolution, genetics, and behavior (2010: 522).

Homo erectus shown with tools. Photo taken at the American Museum of Natural History by KDCosta, 2010.

Though tool use has been documented in other nonhuman mammals, the manufacture and use of tools by humans is an extremely complex behavior. Modern chimpanzees are often recognized for their tool usage, but this usage varies whereas humans consistently use tools. Early humans used tools to process carcasses, and we have evidence of this from the marks left on the bones after contact with implements. Stone tools gave humans an advantage: they no longer needed to compete with scavengers. They could hunt game on their own and/or drive off those scavengers if needed. The increased meat in the human diet meant that humans occupied a predatory niche, and as such necessarily needed to disperse so that their localities could support their needs. While Shipman makes clear that the fossil record supports that expansion of geographic range about 2 mya, the more interesting point, in my opinion, is that in seeking out live game, humans needed to learn about their prey, which opened the door for a more meaningful relationship with animals.

Wild animals are certainly able to communicate with each other, but language has thus far largely been relegated to humans, who have a clearly identifiable syntax and grammar (520). Animals have alarm calls, but there are limits to what they can communicate. For instance, a chimp alerting his troupe about a snake cannot provide details about the snake: The chimp cannot say it is a brown snake. (Or maybe it can, and we just don’t know.) And while educated apes may have a vocabulary of about 400 words, they don’t apply syntax and grammar to those words (520). Language allows humans to share information, and we have developed delightfully complicated means of doing so:

Ritual, art, ochre, and personal adornment are used to transmit information about such concepts as beliefs, group membership, or style, leaving physical manifestations visible in the archaeological record. Nothing interpreted as art, ritual, the use of ochre, or personal adornment has been reported in nonhuman mammals in the wild (521).

Depiction of prehistoric art. Photo taken at the National Museum of Natural History by KDCosta.

As more sophisticated stone tools were developed, humans could pursue larger game. But this might often require collaboration, which encouraged language. Perhaps the strongest example of this is prehistoric art which depicts animals extensively, revealing morphology, coloring, behaviors, and sexual dimorphism (Shipman 2010: 524). It creates a record to be shared with others.

Domestication required humans to select for desirable behavioral traits and control the reproductive and genetic output over generations. They lived in close proximity to the animals, historically even bringing them into the home. Indeed, the physical closeness of humans to animals has allowed some infectious diseases to enter the human population from animal hosts, e.g., measles (dogs), mumps (poultry), tuberculosis (cattle), and the common cold (horses) (529). However, the benefits have outweighed the costs when it comes to keeping animals near—animals are much more than a food source:

The Goyet dog is at least 17,000 years older than the next oldest domesticate (also a dog) … animals were domesticated first because their treatment was an extension of tool making (Shipman 2010: 524).

Animals were domesticated as living tools. They expanded the reach of humans and made other resources more accessible. Animals could provide labor, milk, wool, and opportunities for the production of tools and clothing. And domestication was hedged on an understanding of biology, ecology, physiology, temperament and intelligence.

While much has been made of the monkey who appears to have adopted a cat, such cross-species alloparenting is rare. Humans are the exception. We routinely take in animals integrate them into our families, creating a beneficial relationship. Our connection to Fido may be deeply rooted in our evolutionary history.

Shipman, P. (2010). The Animal Connection and Human Evolution Current Anthropology, 51 (4), 519-538 DOI: 10.1086/653816

Krystal D'Costa About the Author: Krystal D'Costa is an anthropologist working in digital media in New York City. You can follow AiP on Facebook. Follow on Twitter @krystaldcosta.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. mini-me70 9:49 am 01/22/2012

    Pets used to be critical in advancing civilization and still are for some in rural or high crime areas and when they provide needed support to those with disabilities. However, the great majority of pets are simply a huge ecological burden and encourage many people to grow closer to their pets when they refuse to do the heavy lifting required to connect with others people. In modern society pets have become another crutch for people to hobble around on where many people have more love for their pets than they would ever set aside for humans. Over 5% of the US carbon footprint can probably be assigned to the pet burden alone.

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  2. 2. Wayne Williamson 2:14 pm 01/22/2012

    Unlike mini-me…I think that pets have become a great health benefit. With our more sedentary life style(read office work) and fewer kids, having pets provides/forces one to exercise with them. I think there are studies that prove this…none handy for me to post;-)

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  3. 3. geojellyroll 10:41 am 01/23/2012

    Interesting but missing the essence. Cats and dogs are akin to ‘tools’…they have (had) a purpose. However, humans are intelligent and know when a tool is no longer needed. We don’t keep stone axes around.

    ‘Pets’ are surrogate humans. We have have intelligence but this trumped by being social animals. Goldfish or dog or hamster….it doesn’t much matter. We become attached and have real or misplaced empathy. We anthropomorphize a pet’s needs and emotions even when our rational side tells us that it is silly. We bond and the chicken becomes a kid brother rather than a BBQ’d hot wings.

    Now I have to go to the the store and buy kitty treats.

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  4. 4. Quinn the Eskimo 12:34 pm 01/24/2012

    As I type this, my cat, Bandit, is lying upon my wrist! She is one of 5 that cohabit with my wife and me. In general they make better friends than most people I know.

    I’m 63, so I’ve had some time to observe this.

    Dogs are okay, too. Sorta.

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  5. 5. Krystal D'Costa in reply to Krystal D'Costa 10:24 am 01/27/2012

    Wayne and mini-me, there are many studies suggesting the health benefits of pet-ownership—and the CDC is a good place to start. However, at least one study has found older pet owners have a higher than average BMI, so there are likely many context dependent variables that will impact the health benefits. I do understand what mini-me is saying in terms of using a pet as a crutch to avoid other relationships, but I’m not sure this is a majority tendency. In many ways pets are easier to love than humans, no? They don’t have the social and personal complications that other humans tend to have, and they love you unconditionally.

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  6. 6. Krystal D'Costa in reply to Krystal D'Costa 10:28 am 01/27/2012

    geo, what sort of kitty treats did you buy? :)

    We have anthropomorphized pets—there’s little argument from me about that. But the question of why these relationships developed in the first place may be rooted in our evolutionary history as we sought and found new ways to manage and manipulate our environment. It pays to care for your tools, whether it’s a stone axe or a border collie.

    Quinn, Bandit sounds a bit like my younger cat, Blaise, who is happiest when she and my laptop are in my lap.

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  7. 7. Krystal D'Costa in reply to Krystal D'Costa 1:49 pm 01/27/2012

    AiP’s comment policy is located here, and is strictly enforced.

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