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From traditional medicine to witchcraft: why medical treatments are not always efficacious.

Tanaka MM, Kendal JR, Laland KN - PLoS ONE (2009)

Bottom Line: With serious doubts about the efficacy and safety of many treatments, the industry remains steeped in controversy.Low-efficacy practices sometimes spread because their very ineffectiveness results in longer, more salient demonstration and a larger number of converts, which more than compensates for greater rates of abandonment.These models also illuminate a broader range of phenomena, including the spread of innovations, medical treatment of animals, foraging behaviour, and self-medication in non-human primates.

View Article: PubMed Central - PubMed

Affiliation: Evolution & Ecology Research Centre, School of Biotechnology & Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia. m.tanaka@unsw.edu.au

ABSTRACT
Complementary medicines, traditional remedies and home cures for medical ailments are used extensively world-wide, representing more than US$60 billion sales in the global market. With serious doubts about the efficacy and safety of many treatments, the industry remains steeped in controversy. Little is known about factors affecting the prevalence of efficacious and non-efficacious self-medicative treatments. Here we develop mathematical models which reveal that the most efficacious treatments are not necessarily those most likely to spread. Indeed, purely superstitious remedies, or even maladaptive practices, spread more readily than efficacious treatments under specified circumstances. Low-efficacy practices sometimes spread because their very ineffectiveness results in longer, more salient demonstration and a larger number of converts, which more than compensates for greater rates of abandonment. These models also illuminate a broader range of phenomena, including the spread of innovations, medical treatment of animals, foraging behaviour, and self-medication in non-human primates.

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General structure of the model.This figure illustrates the processes through which demonstrators of a treatment can change health state. The parameters are defined in Methods.
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pone-0005192-g001: General structure of the model.This figure illustrates the processes through which demonstrators of a treatment can change health state. The parameters are defined in Methods.

Mentions: The general structure of the model is illustrated in Figure 1 and the symbols used are summarised in Table 1. We assume that individuals are either in a diseased state or in a healthy state. We model the spread of a behavioural trait expressed in treatment of disease. The behavioural trait in question is any innovation, practice or treatment that could potentially affect the outcome of this disease. To model the spread of a behavioural trait, we make the following assumptions. A new behavioural trait arises in (or is invented by) an ill individual who may then demonstrate this practice; others who are ill may adopt the practice upon being exposed to it, and then become demonstrators themselves. In other words, demonstrators convert observers. There is empirical support for the assumption that self-medicative treatments spread through social learning [22]. Observers adopt the trait at a constant rate per demonstrator per unit time. This rate is when the demonstrator is ill and when the demonstrator is healthy. Allowing for different rates of cultural transmission from sick and well individuals is important, since treatments for many ailments, ranging from snake bites to the common cold, are primarily applied when sick, and discontinued, or practiced at a less frequent rate, when the sufferer has recovered. As our models are concerned with the initial spread of a treatment, we assume a constant supply of observers. As the dynamics of the spread of the trait are much faster than demographic changes, there are no explicit births in this model. Death, however, occurs at rate per individual per unit time; there is an additional death rate for individuals with the disease.


From traditional medicine to witchcraft: why medical treatments are not always efficacious.

Tanaka MM, Kendal JR, Laland KN - PLoS ONE (2009)

General structure of the model.This figure illustrates the processes through which demonstrators of a treatment can change health state. The parameters are defined in Methods.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2664922&req=5

pone-0005192-g001: General structure of the model.This figure illustrates the processes through which demonstrators of a treatment can change health state. The parameters are defined in Methods.
Mentions: The general structure of the model is illustrated in Figure 1 and the symbols used are summarised in Table 1. We assume that individuals are either in a diseased state or in a healthy state. We model the spread of a behavioural trait expressed in treatment of disease. The behavioural trait in question is any innovation, practice or treatment that could potentially affect the outcome of this disease. To model the spread of a behavioural trait, we make the following assumptions. A new behavioural trait arises in (or is invented by) an ill individual who may then demonstrate this practice; others who are ill may adopt the practice upon being exposed to it, and then become demonstrators themselves. In other words, demonstrators convert observers. There is empirical support for the assumption that self-medicative treatments spread through social learning [22]. Observers adopt the trait at a constant rate per demonstrator per unit time. This rate is when the demonstrator is ill and when the demonstrator is healthy. Allowing for different rates of cultural transmission from sick and well individuals is important, since treatments for many ailments, ranging from snake bites to the common cold, are primarily applied when sick, and discontinued, or practiced at a less frequent rate, when the sufferer has recovered. As our models are concerned with the initial spread of a treatment, we assume a constant supply of observers. As the dynamics of the spread of the trait are much faster than demographic changes, there are no explicit births in this model. Death, however, occurs at rate per individual per unit time; there is an additional death rate for individuals with the disease.

Bottom Line: With serious doubts about the efficacy and safety of many treatments, the industry remains steeped in controversy.Low-efficacy practices sometimes spread because their very ineffectiveness results in longer, more salient demonstration and a larger number of converts, which more than compensates for greater rates of abandonment.These models also illuminate a broader range of phenomena, including the spread of innovations, medical treatment of animals, foraging behaviour, and self-medication in non-human primates.

View Article: PubMed Central - PubMed

Affiliation: Evolution & Ecology Research Centre, School of Biotechnology & Biomolecular Sciences, University of New South Wales, Sydney, New South Wales, Australia. m.tanaka@unsw.edu.au

ABSTRACT
Complementary medicines, traditional remedies and home cures for medical ailments are used extensively world-wide, representing more than US$60 billion sales in the global market. With serious doubts about the efficacy and safety of many treatments, the industry remains steeped in controversy. Little is known about factors affecting the prevalence of efficacious and non-efficacious self-medicative treatments. Here we develop mathematical models which reveal that the most efficacious treatments are not necessarily those most likely to spread. Indeed, purely superstitious remedies, or even maladaptive practices, spread more readily than efficacious treatments under specified circumstances. Low-efficacy practices sometimes spread because their very ineffectiveness results in longer, more salient demonstration and a larger number of converts, which more than compensates for greater rates of abandonment. These models also illuminate a broader range of phenomena, including the spread of innovations, medical treatment of animals, foraging behaviour, and self-medication in non-human primates.

Show MeSH