The Great Pheromone Myth

Preface

Preface The pheromone concept, derived for insects, was first applied to mammals in the early 1960s. Although there is disagreement as to what constitutes a mammalian pheromone, such an agent is most commonly viewed as an innate biologically derived chemical that induces a well-defined behavioral or endocrine response in an invariant and speciesspeci fic manner. In nonhuman mammals, such diverse functions as sex recognition , courtship, copulation, fighting, nesting, social communication, maternal behavior, and altered endocrine function have been attributed to pheromones. In humans, the choice of a mate, the length of menstrual cycles of women living in close quarters, and even the selection of a seat in a dentist’s waiting room have been said to be influenced by pheromones. Whether humans have pheromones was heralded by Science magazine in 2005 as one of the top 100 outstanding scientific questions of the era, emphasizing the importance of this issue to the scientific community at large. In this book I provide a historical overview of the pheromone concept and the myriad attempts to apply it to mammals. Major studies of the effects of excretions and secretions on mammalian social behaviors and endocrine responses are reviewed in detail, and a critical evaluation is made of claims that such responses are due to pheromones. Based upon both empirical and theoretical grounds, I conclude that mammalian pheromones do not exist despite our continued fascination with the pheromone concept, numerous claims of the chemical isolation of pheromones, and the expenditure of millions of dollars on the part of industry and government to find such entities. The reasons for my conclusion are multiple, as will become apparent throughout this volume. One problem with the pheromone concept x PREFACE is that it dichotomizes stimuli and complex behaviors into two classes— pheromonal and non-pheromonal—logically precluding the existence of multiple classes and continua. A second problem is the nominal fallacy, that is, the tendency to confuse naming with explaining. A third problem with this concept is that it assumes one or, at most, a few species-specific molecules of innate origin, largely impervious to learning and distinct from other types of chemical stimuli, are the motive influences. This is rarely the case in mammals. The interpretation of multiple molecules within specific contexts by dynamic and plastic nervous systems largely defines their biological effects. Learning, which in some cases occurs even before birth, plays a significant role in determining or modulating most odor-mediated mammalian behavioral responses, including a number that involve the accessory , that is, vomeronasal, olfactory system. Although a case can be made that exposure to urine and a number of its natural constituents may influence, perhaps inherently, the endocrine system of mice via the vomeronasal system, multiple chemicals are involved and species specificity is questionable . In some cases such stimuli perturb physiological homeostasis, altering reproductive function via stress. Rather than focusing on one or a few molecules, as per the pheromone concept, evolution seems to have favored adaptations related to the detection of multi-chemical features of the complex and changing chemical environment critical for survival. I am aware that my perspective is heretical and may disturb the sensibilities of some scientists. I am also aware that it is difficult to prove the negative, particularly when definitions lack operational substance and become transmuted repeatedly to fit idiosyncratic contingencies. I only ask that the reader keeps an open mind as the material in this volume is traversed. Although I am under no illusion that this treatise will reverse long-standing beliefs that pheromones mediate many mammalian behaviors , it is gratifying that a growing number of neurobiologists are moving away from the simplistic tenets of the pheromone concept in both their research and theorizing. Hopefully this book will increase awareness, particularly among young scientists, of the complexity of chemical communication and the nature of the influences of biologically derived chemicals on a range of reproductive and other behaviors. I thank the editorial staff of the Johns Hopkins University Press for their willingness to consider my radical perspective on this topic and the Na- tional Institutes of Health, whose financial support has largely made my career possible. I am grateful to those colleagues and friends who provided feedback or encouragement to me during the course of the project, including my intellectual mentor Jack King, Solange Chadda, Mary Lou Derksen, Carol Doty...