In the world of humans, siblings often grow up under the same roof and share a special bond throughout their lifetimes. But what about dogs? Do canines recognize and feel an innate connection with their brothers and sisters?
Social Imprinting
Though there is no concrete evidence suggesting that dog siblings can recognize each other later in life, although Steven R. Lindsay, author of the "Handbook of Applied Dog Behavior and Training," suggests they can. In his writings, Lindsay suggests that a dog can recognize his parents and siblings, and even humans from early interactions, provided they are together during the critical socialization phase from week three of life through week 16.
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A dog's nose usually knows.
It is possible that a dog can recognize a sibling by scent. A dog's sense of smell supersedes that of humans by 10,000 to 100,000, so perhaps this ability allows a dog to detect a littermate he has not seen in years.
Similarly, studies suggest that dogs can remember and recognize individual faces and read facial expressions. Paolo Mongillo from the University of Padua in Italy conducted a study to determine if a dog could recognize his owner's face. When presented with his owner and a stranger, the dog showed preference to his owner, but paid less attention when the owner's face was covered. If a dog can recognize the face of someone of another species, it's plausible that he'll be able to recognize faces of his own, provided they once shared a memorable connection. This, however, is conjecture.
DNA might play a role.
As in humans, dog relatives share DNA, and it is possible that it is this DNA imprinting that keeps a dog from mating with a sibling. According to evolutionary theorists, all living things are innately programmed behave in such a way as to ensure the survival of their DNA into the next generation. Therefore, individuals of all species will take care of its blood relatives first, suggesting species other than humans not only recognize but favor and assist their own family members. However, animals will have to recognize who their siblings are before they can favor them over others -- and that recognition may or may not last an entire lifetime.
Conclusion
The truth of the matter is, no one knows for certain if a dog recognizes that another dog is its sibling. Perhaps one day man will be able to communicate with a dog on a dog's level, but until that day comes, we can only make our best educated guesses.