Figure 1.

Canine Variation

Shown are examples of the cane corso and a Chihuahua mix (A). The cane corso is a large breed weighing, on average, 110 lbs (males) in contrast to the Chihuahua, one of the smallest, sometimes weighing under 3 lbs. Also shown are (B) the pug and (C) Afghan hound, which exhibit dramatic differences in head shape. Most dog breeds were developed in Europe within the last 300 years. The AKC recognizes nearly 157 breeds, although there are about 350 noted worldwide. Breeds differ in phenotype in terms of overall body size, coat color, length and texture, head shape, leg length, and dozens of other attributes.