FIGURE 2.2 One Species, A Billion Variations Dogs immediately recognize other dogs, even from a distance, despite dramatic differences in size, shape, colouring (of tongues and eyes as well as coats), and, as shown here, in hair. Minor code variations become marked for differences—long or short, curly or straight, wiry or limp.

THIRD FROM TOP: GETTY IMAGES/HEMERA/THINKSTOCK; OTHERS: PHOTODISC