Introduction

Dogs are absolutely unique among domestic animals in their association with human caregivers. For one thing, their history with us over evolutionary time is the longest of any domestic species. Secondly, they display an almost unbelievable degree of morphological and behavioral diversity – diversity due almost entirely to their association with humans. Over the centuries, as dogs have been bred for various physical attributes, they have also undergone a variety of changes in behavior. Some breeds have been selected for behavioral changes that are useful in hunting, such as pointing at game birds, chasing foxes while vocalizing, or retrieving waterfowl shot by hunters. In other breeds, behavior associated with the performance of complex tasks, such as herding sheep, has been accentuated. These particular behavior functions that have come to characterize the different breeds of dogs are the outcome of the suppression or enhancement of existing “native” canine behavioral characteristics, rather than the emergence of new behavior patterns (Scott & Fuller, 1965; Lord et al., Chapter 4).

This chapter represents a revised, updated and extended version of a previous review (Hart, 1995) of behavioral differences among 56 popular dog breeds (Hart & Hart, 1985; 1988; Hart & Miller, 1985). Here we report some of the main findings using a new data set involving 80 breeds based on breed rankings derived from telephone interviews with 168 small animal veterinarians.

Extensive research on the canine genome has laid the groundwork for investigations of behavioral differences among breeds that may be related to differences in breed-specific genomes. A particularly useful study with regard to understanding behavioral differences and similarities among breeds of dogs is one that used microsatellite DNA markers to study genetic relationships among 85 breeds (Parker et al., 2004). The same technique was subsequently extended and refined (Parker et al., 2007, 2010). These analyses reveal that almost all dog breeds are genetically distinct and that some can be grouped according to genetic similarity. These genetically similar breed groups provided a means to determine whether the observed breed differences in behavior in the present study had at least some genetic basis.