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CHAPTER OUTLINE 33.1 Nature Versus Nurture: Genetic Influences The “nature versus nurture” question asks to what degree our genes (nature) and environmental influences (nurture) affect our behavior. Behavior encompasses any action that can be observed and described. Nest-Building Behavior in Lovebirds Experiments with nest-building behavior lovebirds suggested this behavior has a genetic basis. Food Choice in Garter Snakes Experiments with garter snakes showed that their food preference was genetically based. Egg-Laying Behavior of Marine Snails All of the egg-laying behavior of the marine snail Aplysia is controlled by egg-laying hormones. Twin Studies in Humans Studies of separated twins show that they have similar food preferences and activity patterns, and even select mates with similar characteristics, lending support to the hypothesis that certain types of behavior are primarily influenced by nature (i.e., genes). 33.2 Nature Versus Nurture: Environmental Influences Environmental influences also affect behavior. Learning is defined as a durable change in behavior brought about by experience. Learning in Birds Laughing gull chicks’ begging behavior appears to be a fixed action pattern, but is, in part, learned. Imprinting Imprinting is a simple form of learning that has a strong genetic component, as first observed in birds when chicks, ducklings, and goslings followed the first moving object they saw after hatching. The behavior develops only during a certain sensitive period. Social Interactions and Learning White-crowned sparrows sing a species-specific song, but males of a particular region have their own dialect. Social interactions assist learning in birds. Associative Learning A change in behavior that involves an association between two events is termed associative learning. Classical Conditioning In classical conditioning, the presentation of two different types of stimuli at the same time causes an animal to form an association between them. This suggests that an organism can be trained or conditioned to associate a specific response to a specific stimulus. Operant Conditioning During operant conditioning, a stimulus-response connection is strengthened. 33.3 Animal Communication Some animals form a society in which members of species are organized in a cooperative manner, extending beyond sexual and parental behavior Social behavior in animals requires that they communicate with one another. Communication is a signal by a sender that influences the behavior of a receiver. Chemical Communication Chemical signals have the advantage of being effective both night and day. The term pheromone designates chemical signals in low concentration that are generally passed between members of the same species. Auditory Communication 1 Auditory communication is faster than chemical communication and it is effective both night and day. Language is the ultimate auditory communication. Visual Communication Visual signals are most often used by species that are active during the day. Tactile Communication Tactile communication occurs when one animal touches another. 33.4 Behaviors that Affect Fitness Much of the behavior of organisms we observe today must have adaptive value. Territoriality and Fitness Animals often have a particular home range where they can be found during the course of the day. Territoriality is actively defending a portion of their territory for their exclusive use as a food source or as a mating area. Territoriality is more likely to occur during time of reproduction. Foraging for Food Animals need to ingest food that will provide more energy than the effort expended acquiring the food. The optimal foraging model states that it is adaptive for foraging behavior and food choice to be as energetically efficient as possible. Reproductive Strategies and Fitness Usually primates are polygamous and males monopolize multiple females. Because of gestation and lactation females invest more in their offspring than males and are concerned with a good food source. Tamarins are polyandrous and Gibbons are monogamous. Sexual Selection Sexual selection is a form of natural selection that favors features that increase an animal’s chances of mating, which lead to increased fitness. Sexual selection often results in female choice and male competition because females have a limited number of eggs and males produce a plentiful supply of sperm. Mating in Humans A study of human mating behavior shows that the concepts of female choice and male competition apply to humans as well as to other animals. Human Males Compete Due to the high investment in having a child by women and the low contribution of men, more men are available and have to compete with others for the privilege of mating. Females Choose Females prefer a mate who can obtain (financial) resources and shows symmetry in facial and body features, related to the “good genes” hypothesis. Men Also Have a Choice Men prefer youthfulness and attractiveness in females, signs that their partner can provide them with children. Societies and Fitness The principles of evolutionary biology can be applied to the study of social behavior in animals. Sociobiologists hypothesize that societies form when living in a society has a greater reproductive benefit than reproductive cost. Sociobiology and Human Culture The culture of a human society involves a wide spectrum of customs. It is proposed that human societies originated because of the need for cooperation, communication, and tools in hunting large animals. Altruism versus Self-Interest 2 Altruism can be generally described as a self-sacrificing behavior for the good of another member of the society. In general, altruistic behavior in animals is explained by the concept of kin selection, which increases an individual’s inclusive fitness. Reciprocal Altruism In some bird species, offspring from a previous clutch of eggs may stay at the nest to help parents rear the next batch of offspring, contributing to the survival of its own kin and increases its chances of inheriting a parental territory. Reciprocal altruism also occurs in animals that are not necessarily closely related; it usually occurs in groups of animals that are mutually dependent. 3