Hundreds of dogs report for duty at airports across the country, trained to sniff out bombs and other explosives for the Transportation Security Administration.
Many have ears that hang low, delightfully dangling around their faces. Some have ears that stand tall and upright, flickering at every sound. All have ears that are, of course, adorable — a 12 out of 10, if you will.
But the T.S.A. has made it clear that it has a preference. The agency said it favors floppy-eared dogs over pointy-eared dogs, especially in the jobs that require interacting with traveling passengers, because floppy-eared dogs appear friendlier and less aggressive.
“It presents just a little bit less of a concern,” the T.S.A. administrator, David Pekoske, said last month during an event at Washington Dulles International Airport. “Doesn’t scare children.”
About 70 percent of dogs in the T.S.A.’s canine program have floppy ears, including Labrador retrievers, German shorthaired pointers and Vizslas. Among dogs that screen and interact directly with passengers, nearly all are floppy-eared because those dogs are generally seen as “friendly” and “good with all ages of people,” said Chris Shelton, who manages the agency’s Canine Training Center.
The T.S.A. also uses some pointy-eared dogs, like Belgian Malinois and German shepherds. Though the agency said it was confident those dogs could do the job, too, some dog lovers did not take kindly to the T.S.A.’s stance. “Seriously, TSA?” one person wrote on Twitter, posting a photo of a pointy-eared dog named Indiana Bones with his toys. “The only things that should fear Indiana Bones and his pointy ears are stuffed hedgehogs and tacos.”
But is the T.S.A. right about floppy ears? Sort of.
There is a scientific explanation for why humans associate floppy ears with friendly animal behavior.
Animals that were domesticated by humans tend to have certain characteristics in common: curvier tails and more juvenile facial features than their wild ancestors — and floppier ears, said Lee Dugatkin, an evolutionary biologist at the University of Louisville.
After nearly 60 generations of breeding for sociable behavior, the foxes in the Russian experiment nuzzle with their human caretakers and have floppier ears and rounder, more dog-like snouts than their wild ancestors.CreditThe Institute of Cytology and Genetics, Novosibirsk
Take the domestication of wild foxes as an example. In the late 1950s, a scientist in Russia named Dmitri K. Belyaev began an experiment, which is still ongoing, to replicate the process of domestication in real time, selecting silver foxes for breeding based on one characteristic: their calmness and friendliness toward humans.
Within about five generations, the foxes, which are in the canine family, began to act more domesticated, wagging their tails and licking people’s hands. After about 10 generations, they started to develop floppy ears, Dr. Dugatkin said.
“The floppy ears, the curly tails and so on, all of those somehow came along for the ride when you choose only based on behavior,” said Dr. Dugatkin, co-author of the book “How to Tame a Fox (and Build a Dog)” with Lyudmila Trut, a Russian researcher who has led the silver fox experiment for the past 60 years.
Researchers have discovered that animals that are calmer and friendlier also have fewer neural crest cells, a type of stem cell that can grow to form other types of cells, including cartilage, Dr. Dugatkin said. “When that manifests itself in ears,” he said, “you have ears that don’t stand up as straight because they don’t have as much cartilage.”
So in an evolutionary sense, the T.S.A. is correct: “People inherently think of these droopy ears as a more juvenilized, friendly kind of trait,” Dr. Dugatkin said.
But in practice, you can’t assess a dog’s personality simply based on its breed or ear type.
“Every dog is different,” said Christa Chadwick, vice president of shelter services for the American Society for the Prevention of Cruelty to Animals. “We don’t make any assumptions around breed tendencies. We really get to know the individual.”
Gary Szymczak, president of the German Shepherd Dog Club of America, said the breed is highly intelligent, trainable and not innately dangerous. “I’ve got pictures of my grandchildren when they were less than a year old in a crate with a German shepherd.”
“It’s not the shape of the ears,” he added. “It’s what’s between the ears that counts.”
On the second point, the T.S.A. can agree. The agency said appearance was secondary to a dog’s ability to do the job. “At the end of the day,” Mr. Shelton said, “we are focused on security and we are putting the best canine available out to do that mission.”
In fact, the dogs are so essential to T.S.A.’s mission that they continue to report to work while the government is partially shut down. And, unlike other T.S.A. employees, the dogs are getting paid — in tennis balls, chew toys and stuffed animals.
“The dogs get their pay every day, which is their toy,” Mr. Shelton said. Government shutdown or not, “we will continue to ensure they get paid daily.”