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After four months apart, my English setter Freckles was reunited with her mother and sister. They sniffed noses for about five seconds and immediately began to play. They ran and wrestled outdoors as if they'd never been separated. I was curious - do dogs recognize family members?
A study from the Cornell University College of Veterinary medicine showed that dogs likely recognize family members. They prefer to approach littermates to strange dogs. This is true even if the littermates have been separated for months.
Kinship Recognition
The ability to differentiate between a close genetic relative and a non-relative is known as kin recognition. Studies have shown two theories of how animals recognize relatives:
- Recognition gene
- Experiential mechanism
There is no evidence to suggest that recognition is based on genes in mammals. Most studies show that kin in dogs are recognized by various factors depending on the relationship. For example, mothers might use different cues to recognize their offspring than siblings would to recognize one another.

Recognition may be based on phenotypes (observable characteristics). The Cornell study showed that dogs are friendliest to others with a similar genome - which can translate to coloring. The English setters in my example are obviously visually different from the beagle that was also wandering around. It's likely that animals can learn the phenotypes of relatives early on in life.
Some species use olfactory (scent) cues to differentiate relatives from strangers. Mothers are often able to identify their offspring within a short period of time by learning their scent. One study showed that puppies recognize littermates and prefer them to other pups. It seems likely that the chemical cues of smell play a role in recognition between animals that spend so much time together before they can even see.
Kin Selection
Kin recognition can help ward off inbreeding. This theory was confirmed in certain plants that will not be fertilized by a gene-sharing plant. Recognition may also contribute to the survival of the animal's relatives. Familiar, related animals may warn each other of danger (ensuring survival), provide preferential treatment in the form of food or behaviors, or even help each other find mates.
So did my dog recognize her family? The three setters almost completely ignored the beagle that was also in the yard. It's true that she's older and was more interested in sniffing than playing, but she didn't get a second glance after the three relatives were reunited. Freckles, my dog, played much more than she usually does. I'm pretty sure they recognized each other but it's probably worth a few more visits in the future to observe them. Until then, maybe they can learn to use texting as a way to keep in touch!

Resources:
People for Animals: Animals can Recognize their Family Members
PLOS One: Odor-Based Recognition of Familiar and Related Conspecifics: A First Test Conducted on Captive Humboldt Penguins (Spheniscus humboldti)
PubMed.gov: Developmental aspects of kin recognition. (Abstract)
Walk the Dog: The methods dogs use to communicate with their own species
Wikipedia: Kin recognition
Wikipedia: Kin selection
woofreport: Dogs Can Sniff Out Family From Friends
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