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 ResearchBlogging.org. 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).

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).

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