Naturalist Konrad Lorenz thought along similar lines, suggesting that a continuum exists across species, with those at one end having extremely specialised instinctive behaviour patterns, and those at the other end having behaviour patterns much more open to purposive control. Not surprisingly, more intelligent species, such as mammals, fall into the latter category.
Among the most publicised claims for the existence of human pheromones is menstrual synchrony. After exposure to supposed pheromones, the menstrual cycles of close friends and room-mates are said to synchronise so at some point their periods overlap. No such pheromones have been identified, and on statistical grounds alone periods will overlap for a significant amount of time in women with slightly differing cycle lengths.
Anthropologist Clyde Wilson of the University of Missouri, Columbia, and biopsychologist Jeffrey Schank of the University of California, Davis, reported that the statistical analyses used in menstrual synchrony studies are flawed in many ways.
Neither is there any convincing biological or evolutionary basis for menstrual synchrony. As anthropologist Beverly Strassmann at the University of Michigan in Ann Arbor explained in a 1997 Current Anthropology article, pregnancy and lactation, not menstrual cycling, takes up most of the reproductive years of women in societies where birth control is not typically practised (societies which presumably reflect the norm during the majority of human evolution).
In the Dogon of Mali, for example, women menstruate less than 130 times in a lifetime. As they are segregated while they menstruate they form an ideal study group. Using hormone profiles and other techniques to overcome the statistical problems, Strassmann found no evidence for synchrony in women who ate and worked together.
All in all, it looks as if “pheromonology” has become a modern-day phrenology, providing simple but false explanations for most chemically mediated social behaviours and endocrine responses, satisfying only those who seek simple answers to complex phenomena. Perhaps once the idea that mammals have pheromones is dispelled, we can work towards an appreciation of the real role chemicals play in their lives.

The two main classes of pheromones said to exist in mammals are “releaser” (biochemicals that elicit particular behavioural responses in others) and “primer” (biochemicals that alter endocrine function in others). In fact, nearly all phenomena attributed to releasers in mammals turn out to depend on learning, context, or novelty. Take mating preferences. When mice of strain A are fostered as babies with mice of strain B, they tend to prefer to mate with B mice rather than with A mice, their own genetic strain. Pheromones need not be invoked to account for this behaviour as it can be explained by the smell of the foster nest: the fostered mice mate mainly with mice that smell the same. The learning of smells can occur before birth, with adult offspring of a number of species, including humans, showing a stronger preference for foods and smells to which their pregnant mothers were exposed.
As for primer pheromones, in mammals most phenomena attributed to them turn out to reflect physiological and psychological responses to abnormal changes in the social and physical environment, such as stress. And when it comes to hormones and the endocrine system, those influences come from many sources.
Another problem with the pheromone concept is that it forces complex behaviours and stimuli into two categories – pheromonal and non-pheromonal, essentially innate and learned. Mutually exclusive categories cannot share attributes or features and so this false dichotomy precludes multiple categories or continua, and so too narrowly represents the diversity of mammalian behaviour.
The evolutionary biologist Ernst Mayr argues that the situation is even more complex, pointing out that the categories of innate and learned are not, in fact, mutually exclusive. In an article in American Scientist in 1974, Mayr infers the existence of “neural programs” that are to varying degrees open or closed to change according to experience – programs that are “translations” of genes. At one extreme are those programs, and the behaviours that go with them, which cannot be modified, and at the other are those which are totally open to modification.

In humans, pheromones have been claimed to influence sexual behaviour, mood, length of menstrual cycles, even which seat people choose in waiting rooms. By 2000, dozens of brands of perfumes and aftershaves contained supposed pheromones, contributing to a multibillion-dollar industry. Even so, in 2005, the question of whether humans have pheromones was listed by Science among the top 100 unanswered scientific questions.
In my book, The Great Pheromone Myth, I argue on both empirical and theoretical grounds that mammalian pheromones do not exist. Parodying Lewis Carroll’s 1876 children’s poem, The Hunting of the Snark, I suggest the half-century-long search for mammalian pheromones has been a snark hunt.
Not only have mammalian pheromones not been found, but the idea oversimplifies the nature of chemical communication among mammals. “Pheromone” has no more scientific value in describing chemically mediated behaviours or endocrine processes than “visuomones”, “audiomones”, or “touchamones” would in describing phenomena created by non-chemical stimuli.
Not surprisingly, scientists do not agree on what defines a pheromone, and attempts by chemists to identify such putative agents have failed. Among the many reasons for this failure is that the basic tenet of the concept – that one or a few hormone-like chemicals, specific to each species, are triggers of social behaviour – is wrong. In mammals, chemically mediated behaviours are rarely hard-wired, and most biochemicals involved in communication between members of the same species are not specific to that species and comprise many compounds, some of them affected by diet, stress and other factors.

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