In the preface to the first volume of this series we set out our aims, which were to encourage fresh perspectives in ethology and provide a forum for new ideas. We still feel that in the perfectly proper search for high stan­ dards of evidence, methodology has tended to remain the master rather than the servant of most aspects of ethological work. It is easy for us all to forget that the kinds of data we collect are largely determined by the kinds of questions we ask. Even an ethologist with the professed goal of providing a straightforward account of behavior must incorporate into his or her descriptions a great many assumptions about the organization of that be­ havior. Inevitably some facets of what went on will have been selected at the expense of others. This is sometimes done, for example, in the service of a theory that the fundamental unit for description is the fixed action pattern. Our point is not that constraints on the collection of data are bad but that the theory which gives rise to the selection of evidence should not be neglected. In the first volume, the choice of topics and authors was based upon our views about the exciting or developing issues in ethology. This volume represents a more opportunistic approach: the articles were selected from among the many offered to us as best conforming to our aims. Neverthe­ less, certain themes do emerge.

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1 Sociosexual Development in Primates.- I. Abstract.- II. Introduction.- A. Definitions.- B. Age Categories.- III. Infancy.- A. Thrusting and Mounting.- B. Intromission.- C. Orgasm.- D. Partner Selection.- E. Presentation Patterns and Genital Touching.- F. Restricted Rearing.- G. Hormones.- H. Conclusion.- IV. Juvenile Period.- A. Sequential Mountings.- B. Seasonal Patterns.- C. Partner Selection.- D. Posturing.- E. Contexts.- F. Interference and Imitation.- G. Restricted Rearing.- H. Conclusion.- V. Adolescence and Adulthood.- A. Male Group Change, Status, and Hormones.- B. Dominance and Mating.- C. Mature Copulatory Patterns in Males.- D. Other Adult Sociosexual Patterns.- E. Male-Male Sexual Behavior.- F. Incest and Cross-Species Copulation.- G. Old Age.- H. Restricted Rearing: Males.- I. Female Behavior: General.- J. Female Mounting.- K. Female Presenting.- L. Female Orgasm.- M. Restricted Rearing: Females.- VI. General Discussion.- A. Comparisons between Nonhuman Primates and Humans.- B. Research Suggestions.- C. Conclusion.- VII. Acknowledgments.- VIII. References.- 2 Homeostatic Motor Processes in Mammalian Interactions: A Choreography of Display.- I. Abstract.- II. Introduction.- III. The Dimensions.- IV. The Splicing of the Flow.- A. Definition of an Actual Elementary Movement.- B. The Necessity for At Least Two Descriptions.- C. The Possibility of Several Descriptions.- D. Anatomy and Movement.- V. The Connectedness of the Flow.- A. Temporal Connectedness.- B. Spaciotemporal Connectedness.- C. Anatomical Connectedness.- VI. Further Hypotheses and Future Fields of Study.- VII. Togetherness within Shared Routes of Convergence.- VIII. Summary.- IX. Acknowledgments.- X. References.- 3 Biological Rhythms as Information Channels in Interpersonal Communication Behavior.- I. Introduction.- II. Brain Rhythms.- III. Other Rhythms.- IV. Information Processing.- V. Research Procedures and Data.- VI. Summary and Discussion.- VII. References.- 4 Animal Play: Problems and Perspectives.- I. Abstract.- II. Introduction.- III. Theories of Play.- A. The Surplus Energy Theory.- B. The Practice Theory.- C. The "Arousal" Theory of Play.- IV. The Characterization of Social Play.- A. How Has Play Been Characterized?.- B. The Analysis of Temporal Sequences.- C. Are Actions Exaggerated When Performed During Play?.- D. Play and Anthropomorphism: Can Play Be Characterized as Being Pleasurable?.- V. The Communication of Play Intention.- VI. Conclusion.- VII. Acknowledgments.- VIII. References.- 5 Exercise, Play, and Physical Training in Animals.- I. Abstract.- II. Introduction.- III. Physical Exercise in Animal Play.- IV. Exercise Physiology and Training Responses.- V. Consequences of the Physical Training Hypothesis.- A. Why Playful Rather than Serious Forms of Activity?.- B. Age Dependence.- C. Play Deprivation and Exercise Deprivation.- D. Warmup.- E. Play with Familiar Objects.- F. Why Only Homoiotherms?.- VI. Aspects of Play Which the Physical Training Hypothesis Alone Does Not Explain.- A. Manipulative Play.- B. Social Play.- C. Diversive Play.- VII. Summary of Predictions.- VIII. Acknowledgments.- IX. References.- 6 My Descent from the Monkey.- 7 The Organization of Aggression and Fear in Vertebrates.- I. Abstract.- II. Introduction.- III. Conditioned Attack and Fear Behavior.- IV. Situations Evoking Unconditioned Attack or Fear Behavior.- A. Pain.- B. Individual Distance Intrusion.- C. "Territory": The Presence of a Novel Object in a Familiar Situation.- D. Presence of an Unfamiliar Environment.- E. Familiar Object in an Unfamiliar Place.- F. Frustrative Nonreward.- G. Thwarting.- H. Low Reinforcement Schedules.- I. Other Situations.- J. Other Types of Responses Evoked by these Situations.- V. Interaction of Situations Evoking Attack and Fear Behavior.- VI. Common Properties of Situations Evoking Attack and Fear Behavior.- VII. Internal Factors Affecting Decision Process 1.- A. Degree of Discrepancy between Observed and Expected Events.- B. Strength of Ongoing Motivation.- C. Hormonal Factors.- D. Experiential Factors.- E. Interaction of Variables Affecting First Stage of Decision Process.- VIII. External Factors Affecting Decision Process 2.- A. Attack and Target Properties.- B. Two Types of Fear Behavior.- C. Blocked Escape Behavior.- D. Other Situational Factors.- IX. Discussion.- X. Acknowledgments.- XI. References.- 8 On Individuality: The Constituents of Distinctiveness.- I. Abstract.- II. Definitions.- III. The Geometric Model of Distinctiveness.- A. Uniform Distribution.- B. Normal Distribution.- C. General Considerations.- IV. Discussion.- V. Summary.- VI. Acknowledgments.- VII. References.- The Principles of Optimal Behavior and the Theory of Communities.- I. Abstract.- II. Introduction.- III. Models of Optimal Diet.- IV. Optimal Models of Habitat Selection.- V. Models of Optimal Sociality.- VI. Speculations and Discussion.- VII. References.