The article by Muller & Schumann (M&S) is both relevant and timely, given recent debates around the use of so-called smart drugs to boost cognitive performance and what the role of the medical profession should be in prescribing drugs such as methylphenidate and modafanil for this purpose.
My main comments relate to the evolutionary aspects of the article and the relationship between drug use and drug addiction. The following comments will help to strengthen the link between drug use and addiction within the framework that M&S outline. This is important because drug addiction is a significant problem in terms of morbidity and mortality – and also because, in a non-trivial sense, drug addiction is what makes drugs interesting. It also needs to be remembered that all drug-taking is harmful or problematic at the level of society and that a significant component of this social harm arises from the high criminality around the production and supply of drugs.
Although M&S briefly acknowledge that the existence of modern drugs may represent a new evolutionary niche, I think this point should be expanded, with particular reference to the cultural aspects of drug taking. Niche Construction Theory (NCT) (Kendal et al. Reference Kendal, Tehrani and Odling-Smee2011) states that changes in the environment are functions of both the organism and the environment and also that changes in the organism are (different) functions of the organism and the environment.
According to NCT, the influence of the organism – humankind in this case – on the environment has led to the construction of a niche where modern drugs and drug-culture are part of the environment. This is an important note; drugs can then be seen as part of the fitness landscape over which selection pressures operate and for which adaptive advantage is gained. In this context, the process of taking drugs constitutes the interaction between the organism and the environment, and through natural selection those organisms that are “better” at taking drugs will survive. This accords with M&S's suggestions for a number of adaptive advantages that accrue from taking drugs.
There are two important consequences of this scenario. One is that social influences on drug taking will be very strong; for example, a drug-culture will exist. This will be an important part of the process of niche construction – according to NCT, the organism and its genetic determinants will have an effect on changes in the environment. The second consequence is that the trait of “drug liking” will have a strong role to play, and this helps to make more explicit the link between drug taking and addiction. To be specific, if adaptive advantage accrues through drug taking and natural selection will favour those who use drugs, then the trait of drug-liking and its genetic underpinning will be promoted. Any predisposition for liking drugs will be perpetuated. A by-product of this will be the perpetuation of addiction in those who have a strong liking for drugs but are unable to cope with the consequences of drug use. A possible pharmacological mechanism for this is a reduction in the number of postsynaptic dopamine D2 receptors, which is seen in those who have a stronger liking for drugs and also in those who have been addicted to various substances including alcohol, cocaine, and heroin (Lingford-Hughes et al. Reference Lingford-Hughes, Watson, Kalk and Reid2010).
We may then suggest that addiction is a gene×environment problem – there is both a cultural influence and a genetic predisposition – in other words, that it is a problem of the niche. In order to reduce the persistence of addiction, the niche needs to continue to develop or a new niche needs to be constructed. One possibility here may be the cultural acknowledgement and acceptance of the proximal mechanisms of psychoactive drug use that M&S outline and the advantages these give. If this were the case, a new niche, or further development of the current niche, by the legitimate manufacture and administration of performance-enhancing, but relatively safe, drugs, such as methylphenidate, MDMA, modafanil, or even ketamine, may allow for an alteration in drug culture such that drug-liking and its genetic underpinning is no longer necessary to drive the selection process.
In other words, drug-taking is much less driven by drug-liking. This may then allow for the diminution in representation of these genes in the population and an alteration in the cultural environment of drug-taking. Both the genetic and environmental underpinnings of addiction will be modified, and a reduction in the prevalence of addiction may occur. One issue with this suggestion is the time frame over which this might happen. Although operations on both the genetic expression and the cultural environment itself may massively speed up the change in phenotype – that is, addictive behaviour – it may still be a very slow process. Mathematical modelling may help in verifying the validity of this hypothesis.
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The article by Muller & Schumann (M&S) is both relevant and timely, given recent debates around the use of so-called smart drugs to boost cognitive performance and what the role of the medical profession should be in prescribing drugs such as methylphenidate and modafanil for this purpose.
My main comments relate to the evolutionary aspects of the article and the relationship between drug use and drug addiction. The following comments will help to strengthen the link between drug use and addiction within the framework that M&S outline. This is important because drug addiction is a significant problem in terms of morbidity and mortality – and also because, in a non-trivial sense, drug addiction is what makes drugs interesting. It also needs to be remembered that all drug-taking is harmful or problematic at the level of society and that a significant component of this social harm arises from the high criminality around the production and supply of drugs.
Although M&S briefly acknowledge that the existence of modern drugs may represent a new evolutionary niche, I think this point should be expanded, with particular reference to the cultural aspects of drug taking. Niche Construction Theory (NCT) (Kendal et al. Reference Kendal, Tehrani and Odling-Smee2011) states that changes in the environment are functions of both the organism and the environment and also that changes in the organism are (different) functions of the organism and the environment.
According to NCT, the influence of the organism – humankind in this case – on the environment has led to the construction of a niche where modern drugs and drug-culture are part of the environment. This is an important note; drugs can then be seen as part of the fitness landscape over which selection pressures operate and for which adaptive advantage is gained. In this context, the process of taking drugs constitutes the interaction between the organism and the environment, and through natural selection those organisms that are “better” at taking drugs will survive. This accords with M&S's suggestions for a number of adaptive advantages that accrue from taking drugs.
There are two important consequences of this scenario. One is that social influences on drug taking will be very strong; for example, a drug-culture will exist. This will be an important part of the process of niche construction – according to NCT, the organism and its genetic determinants will have an effect on changes in the environment. The second consequence is that the trait of “drug liking” will have a strong role to play, and this helps to make more explicit the link between drug taking and addiction. To be specific, if adaptive advantage accrues through drug taking and natural selection will favour those who use drugs, then the trait of drug-liking and its genetic underpinning will be promoted. Any predisposition for liking drugs will be perpetuated. A by-product of this will be the perpetuation of addiction in those who have a strong liking for drugs but are unable to cope with the consequences of drug use. A possible pharmacological mechanism for this is a reduction in the number of postsynaptic dopamine D2 receptors, which is seen in those who have a stronger liking for drugs and also in those who have been addicted to various substances including alcohol, cocaine, and heroin (Lingford-Hughes et al. Reference Lingford-Hughes, Watson, Kalk and Reid2010).
We may then suggest that addiction is a gene×environment problem – there is both a cultural influence and a genetic predisposition – in other words, that it is a problem of the niche. In order to reduce the persistence of addiction, the niche needs to continue to develop or a new niche needs to be constructed. One possibility here may be the cultural acknowledgement and acceptance of the proximal mechanisms of psychoactive drug use that M&S outline and the advantages these give. If this were the case, a new niche, or further development of the current niche, by the legitimate manufacture and administration of performance-enhancing, but relatively safe, drugs, such as methylphenidate, MDMA, modafanil, or even ketamine, may allow for an alteration in drug culture such that drug-liking and its genetic underpinning is no longer necessary to drive the selection process.
In other words, drug-taking is much less driven by drug-liking. This may then allow for the diminution in representation of these genes in the population and an alteration in the cultural environment of drug-taking. Both the genetic and environmental underpinnings of addiction will be modified, and a reduction in the prevalence of addiction may occur. One issue with this suggestion is the time frame over which this might happen. Although operations on both the genetic expression and the cultural environment itself may massively speed up the change in phenotype – that is, addictive behaviour – it may still be a very slow process. Mathematical modelling may help in verifying the validity of this hypothesis.