Larger animals tend to live longer than smaller ones (most of the time). Think about it. Humans live longer than cats, which live longer than a rat, which lives longer than a fly. But why isn’t this true when it comes to animals within their species? A person who weighs 150 pounds will most likely live longer than a person who weighs 300 pounds. They live longer because of increased health risks for the person who weighs 300 pounds. When it comes to dogs’ life expectancy, how can you compare a Great Dane to a Chihuahua? Their anatomic builds are completely different, and their lifespans reflect this. Beyond size, is there an average age of a dog based on breed or other factors? Yes. Let us explore this subject further.