The DNA of Dog Dirt

New York Times
October 2, 2005

Dog-Waste Management


The DNA of Dog Dirt

Twenty-five hundred tons. That's how much manure was produced every day by the 200,000 horses that moved people and goods around New York City in the late 19th century. Much of the manure went uncollected, which posed a terrible problem. (This is to say nothing of the horse urine, the deafening clatter of hooves or the carcasses left to rot in the street.) The manure was so widespread and smelly and unsanitary that brownstones were built with their entrances on the second floor so that homeowners might rise above it.

Like so many seemingly overwhelming problems, this one was resolved, quite painlessly, by technology. The electric streetcar and then the automobile led to the disappearance of the horses, and with them went their dung.

Most of the animal dung produced in today's New York comes from our dogs. (Estimates of the dog population vary widely, but one million is a good guess.) All their poop doesn't just lie there, of course. In 1978, New York enacted its famous (and widely imitated) "pooper scooper" law, and the city is plainly cleaner, poop-wise, than it was.

But with a fine of just $50 for the first offense, the law doesn't provide much financial incentive to pick up after your dog. Nor does it seem to be vigorously enforced. Let's pretend that 99 percent of all dog owners do obey the law. That still leaves 10,000 dogs whose poop is left in public spaces each day. Over the last year, the city ticketed only 471 dog-waste violations, which suggests that the typical offender stands a roughly 1-in-8,000 chance of getting a ticket. So here's a puzzle: why do so many people pick up after their dogs? This would seem to be a case in which social incentives - the hard glare of a passer-by and the offender's feelings of guilt - are at least as powerful as financial and legal incentives.

If social forces get us most of the way there, how do we deal with the occasional miscreant who fails to scoop? After all, a walk through just about any New York neighborhood confirms that compliance with the law is hardly complete. The Parks Department, meanwhile, which conducts regular cleanliness checks of parks and playgrounds, says that dog poop accounts for 20 percent of its "cleanliness failures." Dog poop is plainly far less of a nuisance than horse manure ever was. But if you are, say, a parent who walks two kids to school every day and tries to keep all three of you from experiencing that telltale soft smush of a misstep, it is a nuisance nonetheless.

With horses, the solution was simply to eliminate them. Might there be a way to get rid of dog poop without getting rid of the dogs? It might help for a moment to think of a dog as if it were a gun. Using laws to eliminate guns has proved extremely difficult. A given gun lasts a very long time, and as with dogs, guns are widely loved. But getting rid of guns should never have been the point of gun control; the point, rather, ought to be getting rid of the misuse of guns - that is, the use of guns in crimes. Consequently, the most successful policies are those that directly punish misuse, like mandatory prison sentences for any crime involving a gun. In California and elsewhere, such measures have substantially reduced gun crime.

Similarly, the problem in New York is not so much with dogs per se. So perhaps attending to the real problem - their poop - will prompt a solution.

Here's an idea: DNA sampling. During the licensing procedure, every dog will have to provide a sample of saliva or blood to establish a DNA file. Then, whenever a pile of poop is found on the sidewalk, a sample can be taken to establish the offender's DNA. (Because stomachs and intestinal walls shed so many cells, poop is in fact a robust DNA source; during a murder trial in Indiana in 2002, the defendant was convicted in large part because the dog poop in his sneaker tread linked him to the scene of the crime.) Once the fecal DNA is matched to a given dog's DNA file, the dog's owner will be mailed a ticket. It might cost about $30 million to establish a DNA sample for all the dogs of New York. If people stop violating the law, then New York has spent $30 million for cleaner streets; if not, the $30 million is seed money for a new revenue stream.

Unfortunately, there's a big drawback to this plan. In order to match a pile of poop with its source, you will need to have every dog's DNA on file - and in 2003, the most recent year on record, only 102,004 dogs in New York were licensed. Even though a license is legally required, costs a mere $8.50 a year and can be easily obtained by mail, most dog owners ignore the law, and with good reason: last year, only 68 summonses were issued in New York City for unlicensed dogs. So even if the DNA plan were enacted today, most offenders would still go unpunished. In fact, it stands to reason that the typical licensed dog is less likely to offend than the typical unlicensed dog, since the sort of owner who is responsible enough to license his dog is also most likely responsible enough to clean up after it.

How, then, to get all of New York's dogs licensed? Instead of charging even a nominal fee, the city may want to pay people to license their dogs. And then, instead of treating the licensing law as optional, enforce it for real. Setting up random street checks for dog licenses may offend some New Yorkers, but it certainly dovetails nicely with the Giuliani-era "broken windows" approach to low-level crime.

Before you dismiss the entire dog-DNA idea as idiotic - which, frankly, we were about to do the moment it popped into our heads - consider this: it turns out that civic leaders in Vienna and Dresden have recently floated the same idea. (Indeed, one Vienna politician cited Mayor Giuliani as his inspiration.) Closer to home, an eighth-grade girl in Hoboken, N.J., has also proposed the DNA solution. During a meeting last year of the Hoboken City Council, Lauren Mecka, the daughter of a police captain, argued her dog-poop case. "While adults like yourselves are appalled and disgusted by the sight of the uncollected dog poop that adorns our parks and sidewalks," she said, "it is children like myself and younger who run the greater risk of contact and exposure. We're the ones who ride our bikes, throw our balls and roll our blades on the city's sidewalks. And we're the ones who have our picnics, stage our adventures and carry out our dragon-slaying fantasies on our parks' grassy lawns."

The council, Mecka says today, didn't seem to take her proposal seriously. Why? "They dismissed it, basically, because I was a 12-year-old kid."

Stephen J. Dubner and Steven D. Levitt are the authors of "Freakonomics: A Rogue Economist Explores the Hidden Side of Everything." More information can be found at


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