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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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Multiple episodes of illness and demonstration restricted to sick individuals.The cultural fitness of self-medicative treatments , (left and middle), and probability of spread of treatments (right) plotted as a function of treatment efficacy, . Left (a): cultural fitness ; we set  so that . Middle (b): cultural fitness ; when treatment is prophylactic (). Right (c): The ultimate probability of spread (rugged lines) and the probability of spread from an innovator (smooth lines) for various rates of relapse  (indicated by colour). Unless stated otherwise, parameter values are , , , , , ,  and  (see Methods for interpretation of parameter values).
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pone-0005192-g005: Multiple episodes of illness and demonstration restricted to sick individuals.The cultural fitness of self-medicative treatments , (left and middle), and probability of spread of treatments (right) plotted as a function of treatment efficacy, . Left (a): cultural fitness ; we set so that . Middle (b): cultural fitness ; when treatment is prophylactic (). Right (c): The ultimate probability of spread (rugged lines) and the probability of spread from an innovator (smooth lines) for various rates of relapse (indicated by colour). Unless stated otherwise, parameter values are , , , , , , and (see Methods for interpretation of parameter values).

Mentions: Multiple episodes of sickness typically favour efficacious treatments, and make it more likely in general that treatments will spread compared to single episodes (Equation (4), Figure 5a). Multiple episodes allow demonstrators of efficacious treatments repeated opportunities to convert others to the practice. High efficacy, by enhancing recovery, increases the number of cycles of demonstration, weakening the trade-off between retention of treatment and duration of illness. Even with demonstration restricted to sick individuals, the efficacy of the treatment with the highest cultural fitness (or probability of spread) is typically high in cases where there is a high rate of relapse into sickness (i.e. large ).


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

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

Multiple episodes of illness and demonstration restricted to sick individuals.The cultural fitness of self-medicative treatments , (left and middle), and probability of spread of treatments (right) plotted as a function of treatment efficacy, . Left (a): cultural fitness ; we set  so that . Middle (b): cultural fitness ; when treatment is prophylactic (). Right (c): The ultimate probability of spread (rugged lines) and the probability of spread from an innovator (smooth lines) for various rates of relapse  (indicated by colour). Unless stated otherwise, parameter values are , , , , , ,  and  (see Methods for interpretation of parameter values).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0005192-g005: Multiple episodes of illness and demonstration restricted to sick individuals.The cultural fitness of self-medicative treatments , (left and middle), and probability of spread of treatments (right) plotted as a function of treatment efficacy, . Left (a): cultural fitness ; we set so that . Middle (b): cultural fitness ; when treatment is prophylactic (). Right (c): The ultimate probability of spread (rugged lines) and the probability of spread from an innovator (smooth lines) for various rates of relapse (indicated by colour). Unless stated otherwise, parameter values are , , , , , , and (see Methods for interpretation of parameter values).
Mentions: Multiple episodes of sickness typically favour efficacious treatments, and make it more likely in general that treatments will spread compared to single episodes (Equation (4), Figure 5a). Multiple episodes allow demonstrators of efficacious treatments repeated opportunities to convert others to the practice. High efficacy, by enhancing recovery, increases the number of cycles of demonstration, weakening the trade-off between retention of treatment and duration of illness. Even with demonstration restricted to sick individuals, the efficacy of the treatment with the highest cultural fitness (or probability of spread) is typically high in cases where there is a high rate of relapse into sickness (i.e. large ).

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
Related in: MedlinePlus