The animal on the cover of Gamification by Design is the rhesus monkey (Macacamulatta), a member of the macaque family. These animals are highly social, living ingroups of 20 to 200 individuals where the female to male ratio can be as high as 4:1.In addition to this disparity, each gender has a separate hierarchy system within thegroup. Males—as in other animal species—gain dominance by age and experience,and young or defeated males are often driven away. In contrast, female rhesus monkeyshave a stable matrilineal structure, wherein females inherit their rank from theirmother. Even more uniquely in rhesus culture, younger daughters will also outranktheir older sisters, likely because they are more fertile.Rhesus monkeys have gray or brown fur and hairless pink faces, which are capableof displaying a large range of expressions. On average, their tails are 8–9 inches long,and they weigh 12–17 pounds. Native to South Asia and India, rhesus monkeys livein a wide range of terrain and altitudes, such as grassland, forests, and mountainousregions. They are most active during the day, and can be found in the trees, on theground, or even swimming.Fruit is the primary staple of their diet, but these monkeys also eat insects, seeds, andother plant matter. They are very adaptable, and have become notorious for stealingfood (and other nonedible items that catch their interest) from urban areas.Due to their large population and physiological similarity to humans, rhesus monkeysare often used in scientific research. Infant rhesus monkeys were test subjectsin psychologist Harry Harlow’s surrogate mother experiment, which studied the rolethat the mother-child bond (or lack thereof) has on development. In 1959, a rhesusmonkey named Able earned the distinction of being one of the first two living beingsto successfully return from outer space (the other was Miss Baker, a squirrel monkey onthe same NASA mission). Able was preserved after his death, and is on display in theSmithsonian National Air and Space Museum.