The Social Behavior of Older Animals

12 Grandmothers

chapter 12 Grandmothers I n the animal kingdom, males usually become less aggressive when they are past their prime. However, some females become more combative as they grow older, as typified by the feisty baboon Vecchia, described in chapter 9. In humans, older men are far less violent than young men, while older women often become more self-assertive, although rarely aggressive. This chapter first considers combative older females: the lives of langur monkeys in India; captive vervet monkeys; two wild Canadian wolves, one of them a grandmother and the other prevented from being one; and prairie dogs. It then examines instances where, according to the grandmother hypothesis, elder females expend energy improving the lives of their grand-offspring, such as sperm whales, langurs, and human grandmothers from 150 years ago. Aggressive Grandmothers langur monkeys Langur monkeys living in the vicinity of Mount Abu, Rajasthan, India, lead an exciting if somewhat unusual life, in that they interact closely with people—friendly shoppers who toss them peanuts, chickpeas, or chappatis to munch; angry merchants from whom they snatch and wolf down delicacies; and watchful men who patrol garden crops tempting to both humans and monkeys. As Sarah Blaffer Hrdy described in her book The Langurs of Abu (1977), their tameness allowed her to observe them, and to make notes on their behavior from 3 m (10 ft) away without alarming them. She watched them over a period of five years, from 1971 to 1975, and found that the age of individual langurs was central to the way their society was organized. As is usual with all wild animals, it is difficult to determine the exact age of any one adult, although elderly langurs have eyes that are more deeply 122 ringed with creases. Female langurs, in general, continue to grow after their first young is born, reaching full size by the time they are middleaged —about 12 years old and 11 kg (24 lb) in weight. At this time, they have wider backs and wrinkled, sunken faces. The oldest females have flattened faces, wide nostrils, and bushy manes of silver hair around their faces. They are bony and appear decrepit (misleading, as chapter 13 demonstrates), with various scars and rips in their ears, accumulated particularly in their fighting grandmother years. By middle age, the males have also reached their full body size—18 kg (40 lb)—and are stockier than their younger selves. A langur troop is usually made up of a number of females and their young, along with an alpha male. The prime adult females are socially active among themselves during the day—grooming, hugging, or mounting each other, as well as feeding, resting, and caring for their young. They are the dominant group. As young females grow, they work their way up in the hierarchy to join this exalted circle, while older ones slowly lose rank as they produce fewer young with age. In Hrdy’s research, prime, middle-aged females produced 0.38 young per year, while the four oldsters produced fewer than half as many. A dominance hierarchy reflective of age in langurs is different from that for baboons and Japanese monkeys , species in which the females inherit their rank from their mother and retain it throughout their lifetimes. Dominance affects a huge number of interactions in the daily life of langurs. The bossy prime mothers grab food from an older female if they feel like it, which they often do, or demand that elders move away from a coveted shady spot. If elderly Circle Eyes tried to feed alongside the others , she was likely to be attacked by younger females who demanded her place on a garbage heap, or at the tasty oozing sap of a palm tree. Sometimes their attacks on her drew blood. Needless to say, because of this antagonism by the prime females— usually their own daughters, since it is the males rather than the females who change troops on reaching puberty—the older females tended to keep to themselves. Circle Eyes never approached her troop-mates to initiate any social activity, but avoided them whenever possible. She went off by herself to feed, remaining among her troop-mates only when they were snoozing or absorbed in grooming. The elderly female Sol, named because of her solitary disposition, also socialized little with others (alGrandmothers 123 though she was eager to fight in their defense), and virtually never...