The Social Behavior of Older Animals

1 Evolutionary Matters

chapter 1 Evolutionary Matters B ehavioral zoologists analyze the behavior and adaptations of animals to determine why and how these characteristics developed over time. The reason they evolved was to improve the species’ potential to reproduce. The more offspring individuals produce compared to their peers, the more likely they are to have their genes survive. Yet for most mammals and birds, older individuals are either no longer reproducing , or reproducing at a slower rate than younger adults. Given that reproduction is the bedrock of evolutionary theory, can the lives of social animals who have reached an advanced age be important in evolution? Surely, from an evolutionary perspective, the wiser course would be death rather than an old age where consumption seems to exceed contribution. But since animals do live to be old, there must be an evolutionary reason for this. Older social animals are vital to their group for two main reasons: (1) they have a good genetic inheritance that they pass on to their descendants , and (2) they have extensive experience with their environment and their species’ culture, both of which they share with the younger members of their group. These aspects of their existence, inextricably intertwined, are considered under four headings in this chapter. First, to have survived to old age, senior animals must have good genes in general, including genes involved with a successful personality; as it is in human beings, personality in wild animals is likely to be most fully developed in adults and elders. Older animals also have a vast store of knowledge to impart to younger group members, which is vital in helping their whole group survive and thrive during hard times. Second, some species have females who live fairly long post-reproductive lives, indicating that these elders must be important for some reason. Why else would they be using up resources that could benefit younger breeding animals? Third, some genes are tailored to affect the behavior of aging animals, with positive results for the 10 group as a whole. Fourth, many older animals display nepotism or altruism that can improve the lives of their younger relatives, thereby also enhancing their own genetic heritage. Older Animals as Success Stories Older animals are, by definition, winners, because most of their peers have long since died. They have good genes.1 Over the years, they have survived all the perils that afflict their species—accidents, famine, drought, aggression from within their group, and predation. They may no longer be interested in reproducing, but they usually have a large number of progeny to their credit. They are role models and perhaps mentors to both their own young and those of their peers. Some older individuals within social species are especially important evolutionarily (personality is genetic in large part), because they have been far more successful than other elders in passing along their genes to succeeding generations. Species evolve because, over time, the DNA of certain individuals alters in a way that makes them more adaptable to their changing environment. They produce more successful progeny than others, so that their DNA becomes predominant—they are exemplars of the future for their species. For example, when Beethoven, the beloved male gorilla studied by Dian Fossey (1983), died of old age, he had sired at least 19 offspring; later his sons Icarus and then Ziz and Pablo took over this function. Many of Beethoven’s progeny left the troop, thus widely spreading his genetic inheritance. Like Beethoven, Effie, the top female in his troop, also had a large genetic influence. When she died of natural causes, she left behind at least seven living offspring. These, in turn, produced young of their own, who continued to live and reproduce. Another amazingly successful female was Number 9, a Canadian wolf who, along with 30 others, was introduced in 1995 and 1996 into Yellowstone National Park, where wolves (Canis lupus) had earlier been exterminated (Smith and Ferguson 2005). In 1995, while in an acclimation pen waiting to be released into the park, she mated with a stranger, Number 10, much to the joy of the zoologists, who had not expected such good news in the first year of the transfer. Unfortunately, this male was shot soon after his release. Number 9, alone, wandered outside the park and scratched out a depression in the soil when it came time to give birth Evolutionary Matters 11 to her...