Read the following excerpt: Have you ever seen footage of search and rescue dogs working at disasters? Have you seen movies or TV programs in which dogs are used to find lost children or track escaped prisoners? Search and rescue dogs save many lives, but they also inspire respect and admiration. They go where we can't go, use senses that out-perform our own feeble versions, and they save lives with the help of their expert trainers and handlers. Search and rescue dogs (SARs) are not just born, however. They require a huge investment of time, dedication, training, and patience almost from the day they are born. SAR dogs are carefully selected when they are quite young. Trainers look for dogs that lack aggression and respond well to commands. They also look for a certain mental focus—it can be on a type of play or a special toy—that will enable the dog to work at a single task for a long time. This focus is important to the training of the dog, but also will be required when the dog is searching for and following human scent. What evidence supports the idea that SAR dogs are carefully selected when they are quite young?