BERLIN -- Everyone knows dogs can fetch and sit on command, but they have the brains to do more: A study published Friday indicates they can remember the words for dozens of objects, some of them for weeks.
The findings suggest that mammals developed abilities to understand sounds before humans learned to speak, the study's German authors said.
The researchers found a border collie named Rico who understands more than 200 words and can learn new ones as quickly as many children.
Rico knows the names of dozens of play toys and can find the one called for by his owner. That is a vocabulary size about the same as apes, dolphins and parrots trained to understand words, the researchers say.
"As far as comprehension goes, we see high intelligence and great memory. It's all very remarkable," researcher Julia Fischer of the Max Planck Institute for Evolutionary Anthropology in Leipzig told reporters.
The border collie, a breed known primarily for its herding ability, was able to go to the room with the toys and, seven times out of 10, bring back the one he had not seen before. The dog seemingly understood that, because he knew the names of all the other toys, the new one must be the one with the unfamiliar name.
"Apparently he was able to link the novel word to the novel item based on exclusion learning, either because he knew that the familiar items already had names or because they were not novel," the researchers said in an article in the U.S. journal Science.
A month later, he still remembered the name of the new toy three out of six times, even without having seen it since the first test. That is a rate the scientists said was equivalent to that of a 3-year-old.
Fischer said the project took off when the researchers saw Rico perform on a German TV show several years ago.
To make sure that he wasn't reacting only to his owner's body language and voice, they tested him at his home but with the scientists giving him instructions.
Rico, born in 1994, may have an advantage because border collies enjoy fetching and because he has been learning for years.
But Fischer noted, "This is not conditioning, it's independent thinking."
Rico's learning ability may indicate that some parts of speech comprehension developed separately from human speech, the scientists said.
"You don't have to be able to talk to understand," Fischer said. The team noted that dogs have evolved with humans and have been selected for their ability to respond to the communication of people.
While dogs may be smarter than many people thought, Paul Bloom of Yale University, who was not involved in the study, urged caution.
"Children can understand words used in a range of contexts. Rico's understanding is manifested in his fetching behavior," Bloom wrote in a commentary, also in Science.
Bloom calls for further experiments to answer several questions: Can Rico learn a word for something other than a small object to be fetched? Can he display knowledge of a word in some way other than fetching? Can he follow an instruction not to fetch something?
The German researchers said they plan more complex experiments with Rico and expressed hope their study will lead to more animal intelligence research with dogs.
"Is Rico a genius of a dog or is this a learning ability that many dogs have, or even all dogs?" co-author Juliane Kaminski said. "Those are questions that will clearly interest us a lot in the future."