Pets, health and our extended phenotype

There’s a fun piece in The New York Times on The Healing Power of Dogs that discusses a wide range of health effects linked to pet ownership. The article briefly discusses a range of research that has linked pet ownership to health benefits. For example:

One Japanese study found pet owners made 30 percent fewer visits to doctors. A Melbourne study of 6,000 people showed that owners of dogs and other pets had lower cholesterol, blood pressure and heart attack risk compared with people who didn’t have pets. Obviously, the better health of pet owners could be explained by a variety of factors, but many experts believe companion animals improve health at least in part by lowering stress.

This research is fascinating in its own right, especially for a person who’s only recently started to live around animals… a lot of animals (at last count, 8 horses, 1 horse expecting a foal, 2 cats, 2 dogs, innumerable wild birds, kangaroos and wallabies all wandering onto the property). I’ve noticed a huge difference in my health and mood since the change, but it’s hard to separate the effects of having Basil and Roxy (the dogs), Glitz and Glam (the cats), or the bigger monkeys around (the horses). But the research discussed also touches on two issues that I think are of particular importance to those of us interested in neuroanthropology and the biology-culture interface.

Edited version

The first is that animals often serve as sensory ‘prostheses’ for humans, using their senses to make humans more aware of their environment. I’m drawing the term ‘prosthesis’ from the work of Allen Feldman (1994) on the way that video was used in the Rodney King trial to extend human perceptual abilities (and, in the end, undermine the obvious fact that King had been beaten unlawfully), but my interpretation of the concept probably owes a fair bit to thinking about cyborgs in the work of Donna Haraway (1990). The difference with Haraway, of course, is that the ‘prostheses’ to the human body, in this case, are organic rather than technological.

In fact, animals have a long history of acting as sensory symbiots with humans, as people look to the behaviour of animals in a range of areas. I had an exchange of email with Tim Ingold about this, after he told me that he was interested in the perception of weather. I was reminded that, since moving to the country and taking up residence with all these animals, I had come to perceive the weather, in part, through the actions of animals. When the cows sat down in the fields, or the black cockatoos flew overhead, we could expect rain. When the border collie got nervous and wanted to come inside, he could hear distant thunder. When the dogs got up tight at night, we wonder what they smell or hear that we can’t. Of course, things like seeing-eye dogs and drug-sniffing dogs are refined versions of this, but I suspect that they are much more widespread than an urban population like anthropologists might predict. A young post-doc applied for a grant with me as the sponsor at Macquarie to look at these relations, and I found her work fascinating. She had looked at animals among herders and was proposing to work on dogs in Aboriginal communities — really intriguing stuff about inter-species relationships. Our colleague Agustín also discussed these sorts of inter-species relationships recently at the AAAs, christening the ‘Audrey effect’ after his own dog.

The ability of animals to detect diseases has a range of intriguing implications, including the possibility that our perceptions of our own health might pass through another individual, even an individual of another species. That is, I may turn to a dog to detect disease in my own body because my body is emitting a smell that the animal can detect. Both my body’s boundary is porous (I give off the smell), and the animal’s condition reveals its perceptions, so it’s perceptions are externally legible.

So domestic animal sensory symbiosis points to a way in which we draw on the perceptions of others, including other species, to get information from the environment. But The New York Times story also suggests that our health has contributing factors from other individuals, including members of other species. These pet-effects on health provide another challenge to assumptions that the human body is a closed system. Although we might call the effects of animals on health largely ‘psychological,’ they are obviously physiological in a very material sense, leading to measurable differences in very basic measures of baseline health.

A dynamic systems approach to human health would have to include a fairly large number of non-human organisms that live in complex relationships with us, not only our pets (who influence our health but also depend on us for theirs as well), but also the various organisms that live in our built environments, in the ecosystems we modify, and even within our bodies, dependent upon the types of foods we provide them, just as we depend upon them to derive everything we need for health. In other words, pets are the tip of a fairly large symbiotic iceberg of organisms that live in and on us, and that affect our health for better or worse.


Okay, so I had a chance to rethink this while floating around in the pool (yes, I’m rubbing in the fact that I live in the Southern Hemisphere), and I’m increasingly unhappy with how few examples I gave of the relations between humans and other species. After all, I brought up horses and then didn’t discuss the labor that animals do (and never mind our dependence on them for food — yes, even you, vegans, as without animals, plants wouldn’t get pollinated and wastes wouldn’t get broken down). And I live just over the escarpment from Robertson, where the movie Babe was filmed — and I live with a border collie who tries to ‘herd’ everything, from horses to ride-on mowers — and I didn’t mention the important working animals out there herding sheep, fetching downed game, tracking food, and the like.

But the other thing that struck me as I was floating around is the degree to which the health effects discussed in the NYT article are reciprocal. We recently had an outbreak of equine influenza here in Australia, and it drove home how precarious the health of domesticated animals can be. For example, just as we have high body fat percentages in relation to wild animals, so do our pets and domesticated animals, but domestic animals often outlive their wild counterparts by significant margins. And it would be interesting to note whether or not domesticated animals also had significantly different profiles for cause of mortality, such as less stress-related diseases. Although Daniel and I have discussed Robert Sapolsky’s book, Why Zebras Don’t Get Ulcers, I still wonder if the potential disease profile of our over-weight, pampered Labrador might be significantly different than an animal that had to work a little harder for a feed than just wagging her tail. Granted, humans have more complex emotional lives, but some of the mechanisms that lead to health problems are very old evolutionarily and shared among a wide range of species. Most hormones, for example, are chemically identical in humans and other mammals. So, even though I endorse what Sapolsky argues, is it also possible that we’re having positive health benefits on our pets?

Feldman, Allen. 1994. From Desert Storm to Rodney King via ex-Yugoslavia: On Cultural Anaesthesia. In The Senses Still: Perception and Memory as Material Culture in Modernity. C. Nadia Seremetakis, ed. Chicago: University of Chicago Press.

Haraway, Donna. 1990. Simians, Cyborgs, and Women: The Reinvention of Nature. New York: Routledge.

Sapolsky, Robert. 2004. Why Zebras Don’t Get Ulcers. Third Edition. Holt Paperbacks.

2 thoughts on “Pets, health and our extended phenotype

  1. What a fun post, Greg (except that part about the pool… I hope those black cockatoos are flying overhead right now). The Nature series on PBS in the States just aired a two-part series on “Dogs That Changed the World” which resonates with some of what you are saying. The bit I caught was actually on that sensory extension, which I find a fascinating idea. Here’s the opening blurb: “NATURE’s two-part special DOGS THAT CHANGED THE WORLD tells the epic story of the wolf’s evolution, how “man’s best friend” changed human society and how we in turn have radically transformed dogs.” And the link:

    They have one part on “how dogs’ finely tuned senses are serving humans and saving lives”–“DOGS THAT CHANGED THE WORLD introduced Daisy and Tangle, dogs able to sniff out cancer cells, and Delta, a German Shepherd who can sense changes in the blood sugar levels of her young master. The talents of these special animals are matched by those of tens of thousands of remarkable canines — dogs trained to sense disease and seizures, to assist the physically and emotionally disabled, and to provide comfort, affection, and therapy to their human companions.”

  2. Very interesting post, Greg, and I love what you’re doing with this blog. This post dredged up from my memory an article I read a while ago (and I’m sorry, I can’t remember the source) which suggested that pets may have a negative effect on health. I think the study cited showed that elderly individuals with pets were more, not less, likely to suffer from depression. It was a very counter-intuitive finding, which is probably why it stuck in my mind. I don’t know if any theories were proposed for why this might be the case, although I seem to remember the suggestion that in some cases having pets might lead to a limiting of interactions with other human beings (think of the stereotype of the crazy old lady with a house full of cats).

    That’s very vague, but it does raise the point that the ‘prosthetic’ qualities of animals are probably complex and not necessarily always beneficial.

    On the symbiotic relationships between humans and non-human organisms, yes, absolutely, but I don’t think you need to look at your pets to find this. I was struck recently while reading Ian Bryson’s A Short History of Nearly Everything in which he states that the number of bacterial cells in the human body far outnumber the number of ‘human’ cells. A lot of the systems that we rely on to live and which we think of as being part of ‘ourselves’, like digestion, would not happen without the activity of ‘non-human’ bacteria. And then it’s worth thinking that our human cells are themselves symbiots. Certain organelles in the cell, such as the mitochondria, are in a sense not part of the cell but exist in a symbiotic relationship with the rest of the cell — they have their own DNA and reproduce according to a different schedule from the rest of the cell. My biologist wife tells me that the theory is that the first complex cells were formed by one type of cell ‘swallowing’ another kind way back in the primordial soup. Or as Wikipedia puts it, our current eukaryotic cells have evolved from a “symbiotic community of prokaryotic cells”.

    Viewed in this way, ‘humans’ don’t just exist within symbiotic systems with other organisms, we are complex systems of organisms — and we work for them as much as they work for us.

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