Why dogs eat poop, according to a dog cognition scientist

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Plenty of stuff divides us as people, but there's one thing we can all agree on: poop smells bad.

No matter what you eat, no matter how healthy you are, your excrement doesn't smell good. Sorry, Khloé Kardashian — even you.

Jokes aside, there's a good reason for that human aversion to repulsive smells: It's evolutionary protection.

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The perception of a "bad" smell is what keeps us from eating potential poisons. So the evolutionary logic goes: Ancestors of ours who were able to avoid death/sickness from eating poisonous material survived, while those who didn't have that trait... didn't survive. We are the product of their survival.

And yet, when it comes to dogs, that aversion to "bad" smells doesn't exist in the same way. To put it directly, dogs sometimes eat things that they shouldn't: chocolate, onions, and even waste (poop).

This begs some questions:

  • Why would a dog eat something that could harm it?
  • Don't dogs have an incredible sense of smell?
  • Why would a dog eat poop, which isn't even food?

I know this problem well, as I have an adorable mutt who loves nothing more than to eat things he shouldn't.

Dog cognition researcher Dr. Alexandra Horowitz is an expert in how dogs smell, and how that sense of smell affects how they see the world. She wrote an entire book about the subject, "Being a Dog: Following the Dog Into a World of Smell," published in October 2016.

And she's got answers.

"It's a little bit unsolved why they would eat feces, what the advantage would be when there are disadvantages," she told me in a phone interview earlier this year. But we do have some hints, and the first major hint has to do with how dogs experience the sense of smell comparatively with how we do as humans.

"Smell is just information for them," Horowitz said. "The same way that we open our eyes and we see the world — it's visual information. We're not making judgments about everything we see. 'Is that good? Is that bad? Is that good? Is that bad?' We're just like, 'That's a plant. That's what that is.'"

For humans with sight, it is the primary sense in terms of experiencing life. For dogs with smell, it is the primary sense in terms of experiencing life.

Or, as Horowitz put it: "A dog just smells things — they smell a plant, they smell a person — not that it's a good or bad smell."

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The funniest pictures from the Westminster Dog Show
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The funniest pictures from the Westminster Dog Show
A Bichon Frise stands on a grooming table in the benching area before competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S. February 13, 2017. REUTERS/Mike Segar
A Chinese Crested is seen in the Judging area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017. / AFP / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/Getty Images)
An Old English Sheepdog is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 . / AFP / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/Getty Images)
Sky Guy, an Italian Greyhoud has his hat adjusted as he stands with his handler before competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S. February 13, 2017. REUTERS/Mike Segar
A Norwegian Buhund is seen backstage at the 141st Westminster Kennel Club Dog Show, in New York City, U.S. February 13, 2017. REUTERS/Stephanie Keith
A Berger Picard is photographed after a demonstration of the types of agility tests that will be in this year's Westminster Kennel Club dog show in New York, U.S., January 30, 2017. REUTERS/Lucas Jackson
A parti-color Spaniel is carried by his handler during competition in the Sporting Group during the Westminster Kennel Club Dog show at Madison Square Garden in New York February 16, 2016. REUTERS/Mike Segar
A Dogue de Bordeaux yawns on the sidelines during judging in the Working Group at the 141st Westminster Kennel Club Dog Show at Madison Square Garden in New York City, U.S., February 14, 2017. REUTERS/Mike Segar
Rumor, a German shepherd and winner of Best In Show at the 141st Westminster Kennel Club Dog Show, poses for photographers at Madison Square Garden in New York City, U.S., February 14, 2017. REUTERS/Stephanie Keith
Komondor 'BettyBoop' is seen in the judging area during day two of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 14, 2017. / AFP / TIMOTHY A. CLARY (Photo credit should read TIMOTHY A. CLARY/AFP/Getty Images)
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Dogs have eyes, of course, just as humans have noses — it's a question of primacy. Dogs "see" the world through smell, just as non-visually impaired humans "see" the world through their eyes. It's easy to understand why a dog doesn't smell poop (or potentially toxic foods, like onions and chocolate) and react with revulsion — it's information.

"Given that their primary sensory modality is olfaction [smell], they're experiencing smells merely as information," she said. "They're not identifying them and characterizing them as we identify smells."

That doesn't explain why a dog would then take the next step and eat something potentially dangerous. To understand that, we must first understand what gives dogs such an incredible sense of smell — and that requires a fancy science term (sorry!).

In addition to the nose itself, dogs have an olfactory organ that humans lack: the "vomeronasal" organ. Think of it like an add-on to the nose, capable of detecting the pheromones and other chemical messages communicated within a particular animal species. And it goes a long way in explaining why dogs sniff the waste of other dogs.

"To get information [in the vomeronasal organ], you have to actually absorb some of the molecules," Horowitz told me. "Maybe what they do is consume the thing to get that information."

Put more simply: Dogs could very well be eating poop in an effort to learn more about whatever animal excreted that waste.

"If you were doing it like a scientist, you would just get a very small amount [of poop], put it on the roof your mouth, allow it to be absorbed into the vomeronasal organ, and then get the information about the hormones and so forth," she said. "But dogs don't have that equipment."

Sadly, we don't live in a world full of dog scientists. Not yet, anyway.

Click below for the 2017 Westminster Dog Show dogs ... even they indulge in some poop (probably)

47 PHOTOS
Westminster Kennel Club Dog Show 2017
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Westminster Kennel Club Dog Show 2017
A Boxer named Devlin wins the Working group at the 141st Westminster Kennel Club Dog Show, in New York City, U.S. February 14, 2017. REUTERS/Stephanie Keith
A Brussels Griffon relaxes on its owner's lap backstage at the 141st Westminster Kennel Club Dog Show, in New York City, U.S. February 13, 2017. REUTERS/Stephanie Keith
NEW YORK, NY - FEBRUARY 14: An English Setter competes in the sporting category during the final night at the Westminster Kennel Club Dog Show at Madison Square Garden, February 14, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries. (Photo by Drew Angerer/Getty Images)
A Boxer named Devlin wins the Working group at the 141st Westminster Kennel Club Dog Show, in New York City, U.S. February 14, 2017. REUTERS/Stephanie Keith
NEW YORK, NY - FEBRUARY 14: A Cocker Spaniel competes during the sporting category on the final night at the Westminster Kennel Club Dog Show at Madison Square Garden, February 14, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries. (Photo by Drew Angerer/Getty Images)

A Bichon Frises is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

Adrian, an Irish Setter and his handler Adam Bernardin celebrate winning the Sporting Group judging at the 141st Westminster Kennel Club Dog Show at Madison Square Garden in New York City, U.S., February 14, 2017. REUTERS/Mike Segar

A Cavalier King Charles Spaniel is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

A Bichon Frise is groomed backstage at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Chow Chow is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

A Bulldog is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

An Old English Sheepdog is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

A Pembroke Welsh Corgi waits to compete at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Standard Poodle competes at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

An Italian Greyhound competes during the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A French Bulldog runs during competition at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Yorkshire Terrier runs during competition at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A bulldog rests before competing at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

Italian Greyhounds compete during the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Toy Poodle is groomed backstage before competing at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

Borzoi dogs prepare to take the field to compete at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

An Italian Greyhound competes during the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

Maltese dogs prepare to take the field for competition at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Lhasa Apso is seen in the Benching Area area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

A group of Pembroke Welsh Corgis wait to compete at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

Beagles line up in the judging area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

A Beaucerons is seen in the judging area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

A handler is seen with a Dalmatian in the judging ring during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

Dogs are seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

A Chinese Crested Powder Puff rests with Kristen Riddley in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

A Beaucerons is seen in the judging area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

An Afghan is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

Cavalier King Charles Spaniels are seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

A Standard Poodle is seen in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017 .

(TIMOTHY A. CLARY/AFP/Getty Images)

Half sisters Elsa (2) and Faith (5) represent the South Carolina State dog, the Boykin Spaniel, at the 'Meet the Breed' Day ahead of the 141st Westminster Kennel Club Dog Show, on February 11, 2017 in New York City.

(Photo credit should read Julie McGuire/Barcroft Images/Barcroft Media via Getty Images)

Acela, a three year old Papillon from Long Island, NY, waits to take part in the Masters Agility Championships at the 141st Westminster Kennel Club Dog Show, on February 11, 2017 in New York City.

(Photo credit should read Julie McGuire/Barcroft Images/Barcroft Media via Getty Images)

11 year old Bergamasco Alpine Sheepdog, D'Artagnan, takes a break during the 'Meet the Breeds' day ahead of the 141st Westminster Kennel Club Dog Show, on February 11, 2017 in New York City.  

(Photo credit should read Julie McGuire/Barcroft Images/Barcroft Media via Getty Images)

Cessie, a Coton De Tulear from Beverley Hills, California, sits on the shoulders of owner Jessica Macintire after competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S., February 13, 2017.

(REUTERS/Mike Segar)

A Boxer is wrapped in a blanket after competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S., February 13, 2017.

(REUTERS/Mike Segar)

Sky Guy, an Italian Greyhoud, stands with its handler before competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S., February 13, 2017.

(REUTERS/Mike Segar)

Diamond, a Standard Smooth Dachshund wears a coat and jewels before competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S., February 13, 2017.

(REUTERS/Mike Segar)

A Standard Poodle is groomed in the benching area by his handler before competition at the 141st Westminster Kennel Club Dog Show in New York City, U.S., February 13, 2017.

(REUTERS/Mike Segar)

A Lhasa Apso competes at the 141st Westminster Kennel Club Dog Show, February 13, 2017 in New York City. There are 2874 dogs entered in this show with a total entry of 2908 in 200 different breeds or varieties, including 23 obedience entries.

(Photo by Drew Angerer/Getty Images)

A Yorkshire Terrier rests in the Benching Area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

The Pulik is seen in the judging area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

A Maltese sits in the benching area during Day One of competition at the Westminster Kennel Club 141st Annual Dog Show in New York on February 13, 2017.

(TIMOTHY A. CLARY/AFP/Getty Images)

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