The personality of a dog is flexible and indeterminate. Dogs can be exuberant or shy; friendly or hostile; fearful or bold; aggressive or passive or some combination of the above. These differences in personality may to some extent be determined by breed, or individual genetics, but for the most part it is based on how and to what extent each particular dog has been socialized.
For the health and wellbeing of your dog, training should really not ever be considered an option when owning a dog. Well trained dogs are more likely to be behaved and listen, be void of behavioral issues, be good in public, and are less likely to bite. Owners also have a much closer connection with the dog when the time is taken to form a relationship through training.
A well trained SAR dog is a sight to behold. The dog can evenly maneuver the most difficult of terrain with the grace of a mountain goat all the while looking for a trapped or hidden human being. This type of work is often done on the fly, at the drop of the hat, with little advanced warning. It requires a talented dog and a special handler willing to invest the time and effort.