We can’t expect a dog to behave in ways he was not genetically prepared to behave. Your Fox Terrier is just following instructions when he chases and kills a rabbit in the yard. Despite your repeated scolding, he is not being “bad” or “disobedient.” He is just being a terrier with a genetically intact predatory sequence aimed at killing small mammals.

Other kinds of dogs were genetically selected only to display part of this predatory sequence, and some were bred to display virtually no predatory behavior whatsoever. Needless to say, these historically-based differences in your dog’s DNA are going to matter a great deal (at least to that rabbit).

While you don’t need to be a whiz at the hundreds of dog breeds out there, you do need to know which of the ten genetically distinct working groups your dog belongs to. You need to know what kind of job your dog was born to do. You need to know if he is a natural dog, a sight hound, a guardian, a toy dog, a scent hound, a gun dog, a terrier, a bull dog, a herding dog, or a world dog. Your understanding about his historical purpose—how he was purposefully bred to behave in certain ways—is important to success in your relationship. We need to use our dog’s genetics as a practical point of reference for our expectations about their behavior.

SELF: Self, the last pillar of L.E.G.S.®, is inherently the most ambiguous, as it describes the internal factors that are unique to each individual dog. Age, sex, health, disease, disability, nutrition, stress levels, and personal quirks will all play an important part in your dog’s behavior.

Some of these aspects of the self are obvious. Your female puppy is unlikely to have the problem of lifting her leg to urinate on the sofa, while an intact adult male is extremely likely to exhibit this kind of behavior. A deaf dog is less likely to come when called than one with sharp hearing. And a starving animal is more likely than a well-fed one to guard his food bowl aggressively.

There are times, however, when the effects of the self are more subtle. Often a veterinarian becomes an essential player in these cases, performing tests and helping your dog compensate for physical problems. For example, you might not have realized that Ellie was feeling pain in her hips these past few months; you only noticed that she’d become defensive when your other collie walked by her bed.

Some behaviors are normal and appropriate to sex, age, and development, while others may indicate serious cause for concern. Knowing what to expect as a dog develops, matures, and ages can provide great relief. Your trusted vet will become a critical adviser for you throughout the course of your dog’s life, explaining how everything from fear periods to adolescence to old age can affect your canine friend.