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Study Confirms Animals Use "Armpit effect"
WASHINGTON, April 6 (Reuters) - Researchers said they had confirmed on Thursday what scientists have long believed -- that mothers can smell their young using what is commonly called the "armpit effect."

Studies have suggested that animals -- including humans -- can detect pheromones, which are compounds that, while not aromatic to the conscious senses, are somehow smelled.

In humans these scents are produced under the arms.

Jill Mateo and Robert Johnston of Cornell University in New York tested hamsters to see if mothers could pick out their own young using smell alone.

They took newborn hamsters before their odor-sensing capabilities developed and placed them in unrelated litters to be raised. All they ever smelled were the unrelated foster mother and her young.

Several weeks later, when the females were sexually mature and capable of sniffing out potential new mates, the researchers offered them the scents of a variety of hamsters, including their own biological siblings and the foster siblings they were raised with.

The hamsters were clearly drawn to the scents of the unrelated strangers, the researchers reported in the Proceedings of the Royal Society of London.

The researchers said the study suggested the hamsters were using scent to make sure they did not accidentally mate with a close relative.

"There's no doubt about it. This is the armpit effect in action," Mateo said in a statement.

The scientific name of this phenomenon is "self-reverent phenotype matching."

"It can function in nepotism, when you favor close relatives and need to know how closely related you are to them," Mateo said.

"Or it can help in choosing a mate, so you can avoid breeding with a close relative. We're not saying anything about the function of the armpit effect -- just that it occurs and it is not an impossibility in an evolutionary sense."

The theory is that the animals know what they smell like and compare the scents of others. "We never saw them sniffing themselves, but they certainly know what they smell like," Mateo said. "Because of the way we structured the experiment, there is no other way they could have known the scent of their family."

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