Outline and chapter notes to accompany chapter 8 SOCIOBIOLOGY Dec., 2003 A. SOCIOBIOLOGY DEALS WITH SOCIAL BEHAVIOR Social behavior is defined as behavior which influences the behavior of other individuals of the same species. Sociobiology is the study of social behavior and its evolution. LEARNED AND INHERITED BEHAVIOR Inherited behaviors that are complex are called instincts. Most behavior can be modified by learning, i.e., experience in dealing with the environment. Natural selection can work only on the inherited components of any behavior. Nearly every behavior pattern is at least partly learned and at least partly innate. THE PARADIGM OF SOCIOBIOLOGY The sociobiology paradigm dates from Wilson's book Sociobiology (1975). Shared beliefs within the sociobiology paradigm (Box 8.1) include: 1-2. Behavior is interesting, and much of behavior is social. 3-4. Social behavior evolves, largely by natural selection. 5. Behavior is modified by learning, but only within biological limits, at least some of which are inherited. 6. Learned modifications of behavior are not inherited; only the innate predispositions are inherited, and only these can evolve by natural selection. 7. It is therefore important to distinguish learned from innate components of behavior. 8-9. Methods to be used include lengthy observation and description of behavior, comparisons among populations or species, and measuring reproductive fitness. Critics have charged: 1. that most behavior is learned (especially in mammals), 2. that sociobiology devalues learning by emphasizing inherited traits, and 3. that extrapolations from other species to humans are risky at best. Many of the critics of sociobiology fear genetic determinism or hereditarian bias. RESEARCH METHODS IN SOCIOBIOLOGY Observational field studies usually come first, beginning at a descriptive level. Research questions (hypotheses) are usually posed on the basis of initial field studies or previous research. Most field studies are designed to answer a research question. There are many ways of demonstrating learned or innate components of behavior: 1. Behavior performed by an animal reared in isolation is largely innate. 2. If animals are reared under different conditions or if humans grow up in strikingly different cultures, behaviors which do not vary are largely innate, while learned behavior patterns are expected to vary. 3. If different breeds or strains of a species show consistent differences in behavior, these differences are largely inherited. 4. If two populations differ in behavior, we may examine individuals from one group adopted early in life and raised by the other group. Behavior consistently resembling the population of birth shows an inherited influence; behavior resembling the population of rearing shows a learned influence. In many cases, both influences are present. 5. If a trait is under strong genetic control, then identical twins should show similarities in the trait even if they are reared under different conditions, and should resemble one another more often or more strongly than fraternal twins. INSTINCTS Complex behaviors under strong genetic control are called instincts. Most instincts are stereotyped (they show little variation). Advantages of instinctive control include: 1. no mistakes are made during any learning process; 2. complex behavior can be performed with fewer neurons; 3. variation is minimal, so behavior can be used in species recognition. Instincts typically occur in situations where uniformity and automatic response are adaptive, and where variety and innovation are likely to be inadaptive. Courtship and mating behaviors are instinctive in most species. Other instinctive behaviors include escape responses, nesting and nest-building behavior, territorial behavior, and gestures of threat or submission. B. SOCIAL ORGANIZATION IS ADAPTIVE ADVANTAGES AND DISADVANTAGES OF SOCIAL GROUPS The many biological advantages of social groupings include: ease in finding a mate, increased food-finding ability (in many species), and increased opportunities for defense. Disadvantages include: increased competition for some resources (food, nesting sites), easier spread of infections diseases, and easier spotting by some predators SIMPLE FORMS OF SOCIAL ORGANIZATION Many invertebrate species form simple aggregates without any dominant individuals. Fish schools also appear to be simple aggregates without any dominant individuals. Captive or domesticated animals often form linear dominance hierarchies, or "pecking orders". ALTRUISM: AN EVOLUTIONARY PUZZLE Altruism is defined as behavior that benefits others but lowers the performer's fitness. It is an evolutionary puzzle to explain how natural selection does not eliminate altruism. Mathematical models to explain the evolution of altruism or to test hypotheses about it are often expressed in terms of game theory. Game theory is a type of mathematical model in which individuals or species are compared to players in a game and their characteristics are compared to game-playing strategies. Under simple models of individual fitness, selfish "cheaters" would have a higher fitness than altruists (in populations containing both), and natural selection would therefore favor cheaters. The group selection model, favored by Wynne-Edwards, is that social groups containing altruists are favored over groups containing selfish individuals only. The kin selection model, favored by most researchers, uses the concept of inclusive fitness, which includes the total fitness of all individuals sharing a certain genotype. If I perform an act which lowers my own fitness as an individual, but which raises the fitness of other individuals sharing parts of my genotype, my inclusive fitness may increase. My inclusive fitness increases whenever more copies of my genotype occur in future generations. Altruistic behavior can therefore be selectively favored if it raises the fitness of related individuals sufficiently. Reciprocal altruism is another possible explanation: altruistic acts are favored if individuals who benefit are likely to reciprocate, indirectly benefitting the altruist or the altruist's kin. Several evolutionary models explain reciprocal altruism as an evolutionarily stable strategy (ESS) that favors altruists over selfish individuals. THE EVOLUTION OF EUSOCIALITY Eusocial species share three characteristics: 1. strictly defined castes or subgroups; 2. cooperative brood care; and 3. overlap between generations. Full eusociality has evolved only in two orders, both of them insects: Isoptera (termites), and Hymenoptera (bees, wasps, & ants). Among termites, eusociality is associated with the need to pass on symbiotic microorganisms that help to digest wood. The passing of these symbiotic organisms to other colony members also allows the passing of food and of pheromones (external chemical communication signals). Among Hymenoptera, eusociality is favored by haplodiploidy, a peculiar type of sex determination in which males are haploid and females are diploid. Females under this system are more closely related to their sisters than to their own children; they therefore increase their inclusive fitness more if they help raise their mother's children (their sisters) than if they raise their own. C. REPRODUCTIVE STRATEGIES CAN ALTER FITNESS Reproductive strategies are patterns of behavior, physiology, and other traits related to reproduction. ASEXUAL VERSUS SEXUAL REPRODUCTION Asexual reproduction is reproduction without genetic recombination. It is favored whenever genetic uniformity and rapid reproduction at a small body size are advantageous. Sexual reproduction is reproduction which includes genetic recombin- ation. The most common form of sexual reproduction produces haploid sex cells (gametes) which recombine randomly, resulting in many new genetic combinations. Sexually reproduced offspring vary greatly in nearly all genetically controlled traits, and sexual reproduction is therefore favored whenever future conditions are uncertain. DIFFERENCES BETWEEN THE SEXES Isogamy is a condition in which gametes are all equal in size. Anisogamy is a condition in which gametes are different: larger, nonmotile eggs, and smaller, motile sperm. Egg producers are called female; sperm producers are called males. Parental investment in their offspring is generally higher for females-- each offspring represents a greater investment of reproductive effort, including stored food, gestational effort, and parental care. Females tend to become more discriminating in mate selection, while males mate more indiscriminately and more often. MATING SYSTEMS Monogamy-- mating between one male and one female, often resulting in cooperative parental care and permanent pair-bonding. Polygyny-- mating between one male and several females. Polyandry-- an uncommon form of mating between one female and several males. Promiscuity-- both sexes mate with multiple partners and avoid permanent partnerships. D. PRIMATE SOCIOBIOLOGY PRESENTS ADDED COMPLEXITIES Primates are an order of mammals that includes monkeys, apes, lemurs, and humans. All primate species are social, and most are highly social. PRIMATE SOCIAL BEHAVIOR AND ITS DEVELOPMENT Primate behavior develops in a social context. Young primates need to cling to soft, cuddly surfaces in order to develop normal behavior. Young primates also need opportunities for social play (especially rough-and-tumble play with body contact) in order to develop normal sexual behavior as adults. Grooming is a pleasurable body-contact activity for primates of all ages, and is most important to the social development of young primates. Savanna baboons have a complex social organization, described on our Web site under Resources: Baboons. REPRODUCTIVE STRATEGIES IN PRIMATES Sexual dimorphism (anatomical differences or size differences between the sexes) is greater when males and females have very different social roles. Male primates typically maximize their fitness by forming alliances with other males and by mating as often as they can. Female primates typically maximize their fitness by caring for their young and also by more subtle strategies. For example, females may secure the protection of high-ranking males by copulating with them; even if no offspring are produced, the male knows that he has mated with that female and he therefore protects both the female and her offspring. In pre-agricultural human societies, men were primarily hunters and women gathered plant foods. Adrienne Zihlmann studied early human fossils and found them to show very little sexual dimorphism. From this, she reasoned that gathering (an activity that produces little dimorphism) evolved early and that hunting (an activity which produces increased dimorphism) came later. SOME EXAMPLES OF HUMAN BEHAVIOR Alcoholism has components which vary according to culture and social standing. One type of male-limited, early-onset alcoholism shows strong hereditary components: sons born to fathers with this type of alcoholism show a much higher rate of this type of alcoholism, even if adopted into nonalcoholic families. Other types of alcoholism show stronger environmental influences. Sexual orientation: much less evidence exists on this. Among homosexual men who have twin brothers, the rate of homosexual orientation is higher among identical twin brothers than among fraternal twin brothers. This suggests some genetic influence, but there are methodological problems with such studies and many other influences are probably also present. Rape is theorized by some researchers to persist because it increases the fitness of rapists. However, the majority of males can achieve greater fitness through faithful sexual relations, which explains why most men are not rapists. ---------------------------------- Dec., 2003 PERMISSION IS HEREBY GRANTED to instructors who have adopted the book BIOLOGY TODAY for classroom use to download, modify, and use these notes as needed to aid them in in their teaching. Students of such instructors may likewise use and modify these notes as study aids.