Humans love drugs. Give us something that causes some alteration in our state that we find pleasing and we can’t get enough of it. We smoke tobacco, drink alcohol, roll spliffs and joints of cannabis, snort cocaine, drop acid, shoot heroin, mix speedballs, pop pills, make meth, chew coca leaves, trip out on mushrooms, brew coffee and countless other activities that get us high, wasted and otherwise ‘state altered’. I’ll be honest here, stranded on a desert island I’d be getting the first batch of coconut wine on the go before I even thought about building a signal fire.
Human history is a litany of drug-fuelled escapades. Genghis Khan’s son Ogedai died from an excessive consumption of wine. The Aztecs were keen users of Psilocybe mexicana, a psychedelic mushroom. Both the Aztecs and the Maya consumed the seeds of the morning glory plant that contain ergine, a compound related to the powerful hallucinogen LSD. The blue lotus flower, a beautiful water lily, was sacred to the Egyptians as a symbol of the sun but it also contains a psychoactive substance called aporphine that was also known to the Maya across the Atlantic. In more recent times, Britain went to war with China twice over the opium trade in the 1800s. Chewing on plants or smoking bits of them to get wasted is one thing, but once the technology of alcohol brewing got under way we could get our buzz on whenever we liked. Exactly when we first realised that we could make booze is much debated, but the discovery of a 13,000-year-old residue of beer in a cave near Haifa in Israel strongly suggests we’ve been at it for a fair time. The burgeoning gin and craft ale markets are strong signs that we’re not stopping in our quest to get state-altered.
The ubiquity of drug use across human culture was noted by the German scientist Baron Ernst von Bibra. Von Bibra was quite something; he was one of those nineteenth-century characters you come across every so often that make you wonder how you’ve never heard of them before. Born in 1806 in present-day Bavaria, this remarkable polymath published on a dazzling range of topics, most of which he helped in some way to define, including industrial chemistry, archaeological metallurgy, chemical archaeology, zoology and botany. He was fortunate, or particularly talented, to survive 49 duels as a young man and, perhaps not coincidentally, went on to develop a special interest in narcotics. In a book examining the cultivation, preparation and consumption of various plant-derived intoxicants from around the world, Die narkotischen Genussmittel und der Mensch (translated as Plant Intoxicants: A Classic Text on the Use of Mind-Altering Plants), he notes that: ‘… there exist no people on the Earth that fails to consume one or another of these dainties, which I have subsumed under the name “pleasure drugs”. There must therefore exist a deeper motive, and the notion of fashion or the passion for imitation cannot be applied here.’
The search for that deeper motive, and how it conflicts with the modern world in ways that are both spectacularly mismatched and incredibly harmful, is what this chapter is all about.
The burden of drugs
The costs of drug-taking are great. If we reduce it to the financial burden, and we accept that putting a cash value on some of the negative effects of drugs is problematic but not impossible, then a recent estimate put the cost just in the USA at a staggering $820 billion (£650 billion) a year.1 The cost of alcohol abuse in the UK alone is estimated to be £55.1 billion.2 We can subdivide this figure to give more of an idea of the breadth and depth of the burden caused by our love for booze: £22.6 billion is the cost to individuals and households through crime, violence, private health care and lost income due to unemployment; a similar amount goes on the human cost of pain and grief; £3.2 billion on NHS healthcare; £5 billion on social care, fire services and criminal justice services; and £7.3 billion on lost productivity and absenteeism. Smoking tobacco accounts for 2 per cent of the world’s entire gross domestic product and kills more than 2 million of us every year.3 Moving to ‘harder’ drugs, more than 70,000 Americans died from drug overdoses in 2017. That figure is up nearly 10 per cent from the year before and the dramatic rise is being driven by a 13-fold increase in the use and abuse of synthetic opioids over the decade from 2007.4 Opioid painkillers available both on prescription and illegally include oxycodone (‘hillbilly heroin’), hydrocodone (Vicodin, favoured by Hugh Laurie’s TV character House MD) and fentanyl, from which musician Prince died of an accidental overdose in 2016. The abuse of opioids in the USA is described variously as ‘a crisis’ and ‘an epidemic’ and has sparked legislative moves to prevent and treat addiction. Despite the declaration of a State of Emergency by the United States Department of Health and Human Services in 2017 and the senate-passed Opioid Crisis Response Act of 2018, the crisis continues. The abuse of drugs is, without any doubt at all, a massive burden on societies around the world.
Against this terrible backdrop of human suffering, financial cost and death it is not surprising that we have tended to become conditioned, at least at a societal level, into thinking that ‘drugs’ are ‘bad’. Such thinking isn’t the consequence of some recent awakening. The Gin Act of 1751 was enacted to reduce spirit consumption, which was seen as a major driver of crime in London. The Temperance movements of the nineteenth century fought a ceaseless battle against the bottle. In recent times, we have the ‘war on drugs’ and countless public health warnings, advertising campaigns and police crackdowns. Our feckless use of drugs is clearly endangering our personal health and well-being and having serious knock-on effects to wider society, but can we once again seek an explanation in a mismatch between our evolutionary heritage and the modern world we have created? The answer is a solid yes, but to understand why we first have to take a far less judgmental view of drug taking.
Drugs are bad, but oh so good…
‘Drugs are bad’ is a society-level way of thinking. At a society level, such a statement is clearly correct and nothing I am about to write will suggest otherwise. Nonetheless, that mind-set conflates the effects that drug consumption has on society with the effects that the drugs themselves have on individual drug users, especially in the short term. If we are to understand why we take drugs from an evolutionary perspective and why the modern world is such a mismatch for the evolved beasts that we are, we need to take a more honest and mature perspective; we need to accept that drugs make people feel good. Really good.
The taking of state-altering chemicals, from Heineken to heroin, from weed to wine, or from cocaine to caffeine, changes the way that people feel. Depending on the substance taken the user may experience feelings of euphoria, elation, invincibility, hyper-alertness, strong emotional bonds with other people (especially fellow users) and the removal of pain, anxiety and doubt. We may become more alert, our senses more attuned, or we might slip into a state of extreme relaxation or a richly tapestried dream-filled sleep. These strong and usually desirable changes in state mean that taking drugs, at least initially, is a very much a good thing for the user in terms of their enjoyment of life. Some drugs might cause users to experience hallucinations and other strong psychological effects. Much is written about the terrors of hallucinations and ‘bad trips’, but many more people take good trips that enhance rather than reduce their life experience.
It is all too easy for the word ‘drugs’ to become shorthand for ‘illegal’ and ‘harmful’ substances like cocaine, heroin and crystal meth, but legally and widely used alcohol has strong and pleasurable effects that are familiar to most people. The line between what is socially acceptable and legal in terms of state-altering substances and what is socially unacceptable and illegal is increasingly blurred by the debate over the legal status of cannabis and so-called legal highs. The drawing of this line is a matter for politicians (ideally, but not always, informed by science-based evidence), but regardless of where it is drawn we will continue to take drugs because taking drugs makes us feel good. They even make us feel good in the face of sure and certain knowledge of the harm they can do both to some individuals and to society overall. Bans, laws, draconian judicial measures, overdoses and human ruin have never, and will never, stop us from taking drugs. Because, and it’s worth saying this again, they make us feel good.
The ‘reward pathway’
From an evolutionary perspective we can understand why we continue to take drugs, despite the knowledge that they could do us harm in the long run, by considering what pathways in the brain are stimulated by drugs and examining what other stimuli evoke similar responses. Fortunately, despite many drugs being very different chemically, there is a tendency for many of them to be rather similar in terms of their effects on the brain. Specifically, many drugs have an effect on a pathway called the mesolimbic pathway or, as it is more descriptively known, the reward pathway. This pathway, when stimulated, releases dopamine (a neurotransmitter that we’ve met before in Chapters 4 and 5) that has multiple effects. First, it regulates what is termed ‘incentive salience’, or the desire and motivation for rewarding stimuli, more of which shortly. Second, it facilitates reinforcement learning, allowing the brain to form connections between stimuli and reward. It may also be involved in the subjective experience of pleasure.
The rewarding stimuli that are usually involved with the mesolimbic pathway fall into two categories.
• Intrinsic, primary stimuli are those things that are good for survival and the production of offspring; sugary food and sex fall neatly into this category. The mesolimbic pathway has been selected for and evolved as a mechanism to incentivise us, and to train us, to seek out things that keep us alive and reproducing.
• Extrinsic stimuli are things we have learnt through the secondary actions of the mesolimbic system to associate with pleasure, like watching a favourite team win or buying a new pair of shoes.
Ultimately the mechanisms involved in drug taking are biochemical, with substances acting at a molecular level in our brains, but for the user the effect is ‘felt’ at an emotional and physical level. Taking drugs stimulates us to feel, often in a highly magnified way, the euphoria and excitation that we have evolved to feel in response to stimuli that were vital for our survival. The ‘high’ we might get from a successful hunting expedition, from a fruitful foraging trip or from sex are evolved responses, producing a pleasurable sensation that we recreate by repetition. When that high is replaced, and greatly accentuated, by the high we get from drugs our brains respond in much the same way and we seek out more of the same.
This explanation for why drugs are so effective is known as the ‘hijack hypothesis’. The idea behind the hypothesis is that drugs ‘hijack’ our mesolimbic reward system, generating a signal that the drug taking is a behaviour conferring a fitness advantage. Anything that feels this good can’t be bad, right? The hijacking of pre-existing, evolved brain machinery is a powerful and intuitive explanation for drug taking that frames our modern world behaviour in a firmly evolutionary context. It also explains drug-seeking behaviour in non-humans.
Many species have been known to develop more than a taste for alcohol, from close relatives like chimpanzees to far more distant relatives like horses. When it comes to harder drugs, rats have proved to be especially useful models for studying their effects. We already know a great deal about rats, they are relatively easy to work with and, like us, they are absolute drug-hoovers if given the opportunity. Rats can be connected to a drug dispenser that will provide a measured dose of whatever drug you wish to test in response to the rat pushing a bar in the cage that dispenses the drug. The rat pushes the bar and gets a hit, perhaps of cocaine. The drug is dispensed down a tube that can be connected directly to the nucleus accumbens in the brain. The nucleus accumbens is a region at the base of the forebrain that is an important part of the mesolimbic, or reward, pathway. When the rat presses the bar, the cocaine is mainlined directly into the brain pathway where it causes the release of dopamine. As we have seen, not only does this dopamine release stimulate the reward pathway, it also reinforces the behaviour of taking the drug, teaching the rat’s brain to repeat the bar pushing.5 And repeat it they do. Rats will enthusiastically learn to self-administer cocaine in this experimental set-up and the brain pathways being activated are identical to those in our own brains. The same result is found if the rats are connected up to a dosing machine loaded with heroin or morphine, again dispensed straight into the mesolimbic pathway. The message from these sorts of experiments is very clear; from an evolutionary perspective, rewarding some behaviours is good. As far as our brains are concerned, drugs provide very effective rewards.
From use to abuse and addiction
The continuation of drug-taking behaviour, whether in humans or rats, can result in a state of addiction. Addiction can become a complex topic both biologically and sociologically, with definitions of what is or isn’t ‘addictive’ combining with confusion between addiction and dependence to create important but tricky problems. My natural tendency would be to swerve the topic altogether and move on to the special challenges presented by the modern world, especially given that the hijack hypothesis seems to so neatly explain our drug-taking tendencies. However, addiction is one of the major costs of drug taking, whichever way we choose to quantify it. What is more, although I have focused on drug taking there are many other aspects of human behaviour that involve, at least in everyday language, ‘addiction’. We are increasingly seeing a narrative develop around mobile technology use, for example, that frames our incessant and seemingly out-of-control use of it, and of the social media supported by it, as addiction. Gambling can also lead to addiction and this has, as we shall see, plausible roots in our evolutionary past. Sex, sugar, even shopping, can also fall into being ‘addictions’ and, when they reach that level, can become highly problematic for people unable to control and change their behaviour. The hijack hypothesis neatly explains why we take drugs, and the learning of extrinsic stimuli in relation to our reward pathways might explain why we pursue other potentially harmful behaviours, but in the context of the modern world this is only the start. The harm of drug taking (excluding early overdose) generally comes once the behaviour is well established and an individual graduates from ‘user’ to ‘addict’. This step has to be understood if we are to understand fully just how badly the modern world we have created interacts with our evolutionary past, not just for drugs but for other behaviours that are of increasing concern.
Having said that addiction is a complex problem, the biological connection between drug use and drug addiction is refreshingly simple. Addiction is generally defined as a disorder of the brain’s reward system, characterised as a compulsive engagement with rewarding stimuli despite adverse consequences. In other words, the taking of drugs that stimulate the reward pathway stimulates the release of dopamine that helps the brain to learn to ‘do more’ of the behaviour being rewarded; a destructive, positively reinforcing feedback loop. A major characteristic of addiction is the breakdown of self-control over intake (we have met self-control before in Chapter 7). Cravings develop through interactions in several brain regions6 and subsequent interactions with the reward pathway. Those cravings push the addict towards behaviours that will bring forth more of the drug but also of course towards the behaviours that society ends up shouldering as the costs of drug addiction: robbery, burglary, violent crime and so on (with clear links to issues raised in Chapter 7).
The repeated use of drugs trains our reward system and can lead to addiction. Some drugs, though, can have other more drastic neurological effects. With repeated use of heroin, for example, users can become dependent. Dependence develops because repeated use means that neurons within the thalamus and the brainstem, separate and different from the reward pathway, adapt to functioning in the presence of that drug. These neurons become unable to function normally if the drug is absent. If the user stops taking the drug in question then they will experience the unpleasant suite of symptoms that create ‘withdrawal’. These are physical symptoms that vary with the drug. The classic heroin ‘cold turkey’ symptoms include extreme anxiety, sweating, shaking, vomiting and diarrhoea and are brought about by the sudden and complete withdrawal of the drug rather than a carefully dose-controlled reduction of intake. Withdrawal can be medically serious, and the sudden withdrawal of some substances upon which a person has become dependent can be life-threatening (as is the case for example with benzodiazepines and barbiturates). Withdrawal symptoms typically follow a pattern of feeling dreadful, and then feeling much worse, until the withdrawal is complete. The only way to alleviate those symptoms is to take more of the drug that has resulted in dependence, which of course combines with addiction (via the reward pathway) to create a very strong drive indeed to get hold of that drug. It is that strong drive that is at the root of much of the crime-related cost that drug taking imposes on society.
Addiction and neurological dependence are physiological conditions predicated on well-characterised interactions between certain substances and our brains. Complementing these physical conditions, psychological dependence is also a strongly motivating force in drug-taking behaviour. Symptoms of psychological dependence include panic attacks, dysphoria (a profound sense of unease or dissatisfaction), a reduced motivation or ability to experience pleasure (known as anhedonia) and our old friend stress (Chapter 5). Psychological addiction is also based on biochemical processes; ultimately everything we think or feel is chemical. Dependence is likely caused by changes in neurotransmitter activity or changes in the way that receptors in the brain work. Once again, dopamine seems set to play an important role.
It is all too easy to think of dependence and withdrawal in terms of ‘hard’ drugs, illegal substances like heroin causing the agonising writhing of threadbare junkies in some filthy badly-lit drugs den. However, dependence and withdrawal are not always so ‘exotic’. In 2007 an article in the medical journal The Lancet compared the harm of drugs by devising a scale that scored the physical harm, the likelihood of dependence and the social harm of 20 drugs using nine categories scored from 0 to 3 by an expert and experienced panel.8 Top of the shop was heroin, then cocaine, barbiturates and street methadone, an opioid used under prescription to manage the symptoms of opioid withdrawal but which is itself an addictive opioid with a street value and abuse potential. However, coming in at number five is the drug of choice for a great many of us in all walks of life: alcohol. Alcohol dependence and withdrawal are so serious that, like benzodiazepines and barbiturates, sudden withdrawal can be life-threatening. At number nine, just one place below amphetamine, is another everyday drug of choice, tobacco, that scores higher than cocaine for physical dependence (1.8 out of 3 compared to 1.3 for cocaine) and just 0.2 behind cocaine in terms of psychological dependence (a whopping 2.6 out of 3 for tobacco and a slightly higher 2.8 for cocaine).
Politics as ‘environment’
The paper’s lead author was Professor David Nutt, an English neuropsychopharmacologist, a job title that would be difficult to say after too many glasses of wine. Nutt specialises in the study of drugs and their effects, including addiction. His work is worth a short digression here because it tells us something about the modern environment in which we, as ‘pre-adapted drug-users’, operate. That environment includes, as we’ve seen in Chapter 7 and will see in Chapter 9, the media but it also includes the political climate in which we live.
If the name David Nutt is familiar to you then it’s likely because he is no stranger to controversy. In 2008 he was appointed as the chairman of the Advisory Council on the Misuse of Drugs (ACMD), an advisory public body in the UK that was formed in 1971 following the Misuse of Drugs Act passed that same year. As chairman of the ACMD, Nutt found himself at loggerheads with a government more concerned about making political capital than considering empirical evidence. In 2009 Nutt published an editorial in the Journal of Psychopharmacology entitled, ‘Equasy – An overlooked addiction with implications for the current debate on drug harms’. If you haven’t heard of equasy, don’t worry, it’s not that you need to become more attuned to the latest shifts in societal drug habits. Nutt was being deliberately provocative in the editorial by comparing the risks of horse riding (horses being equids) with ecstasy (3,4-methylenedioxy-methamphetamine or MDMA), hence equasy or Equine Addiction Syndrome. In the editorial, which is well worth a read, Nutt outlines the considerable risks and harms associated with horse riding and concludes that there is a ‘serious adverse event’ every 350 exposures.9 The harm caused by horse riding can include serious paralysis and even death (10 people per year). Ecstasy on the other hand has one adverse event every 10,000 exposures. Using the scale used in the 2007 paper, Nutt concludes that horse riding is far more harmful than ecstasy and yet society feels no need to control this activity.
Nutt wasn’t suggesting that horse riding should be banned. Instead he proposed that we take a mature and rational approach to the actual risk of harm from drugs rather than the perceived risk of harm, the portrayal of which may be politically motivated (the ‘war’ on drugs being a vote winner on many levels) and exaggerated by the media. The highly biased nature of media coverage of drugs deaths is highlighted by a study, cited by Nutt and published in 2001, which showed that only one in every 250 deaths by paracetamol in the preceding decade was covered by the media but that every single ecstasy-associated death got the full media treatment.
Nutt’s editorial calling for a rational, evidence-based approach did not play out well in a political environment already primed for yet more legislative control of drugs. In returning cannabis to the status of a Class B drug, the then Home Secretary Jacqui Smith had, the year before, gone against the recommendations of the ACMD who had voted (by a majority of 20 to 3) to retain its Class C status.10 By 2009 Smith and others were pushing to keep ecstasy as a Class A drug despite evidence suggesting that the harm it caused did not warrant this status. In February 2009, following Nutt’s editorial, Smith called for him to apologise for his (factually accurate) comments that more people died from horse riding every year than ecstasy, a position that was described as ‘bullying’ in the British Medical Journal. In October 2009, a pamphlet was published containing a lecture that Nutt had given in the July of that year in which he had reiterated his view that drugs should be classified using an evidence-based approach underlined by the actual harm they cause. This was the final straw for a government invested in a public image of being hard on drugs and the new Home Secretary Alan Johnson dismissed Nutt from his role. Nutt may have had a challenging 2009 but things did not go well for Smith that year either. Embroiled in the MP expenses scandal over her true place of residence, in February it emerged that she had claimed expenses for a telecoms bill that included pornographic films watched by her husband. Never let it be said that the environment we have created in the modern world is simple…
Potency and availability
The hijack hypothesis explains, at a neurological and evolutionary level, our penchant for drugs but on its own it does not explain any potential ‘mismatch’ between evolution and environment. To address this, we need to look at the other side of the equation: our modern environment. As we’ve already seen, when it comes to drugs we can subdivide ‘environment’ in a variety of complex ways that include wider social contexts and the political institutions under which we live. Rather than focusing on the role of politics and society in controlling drug, taking, and getting enmeshed in arguments well away from biology and evolution, I would like instead to consider the environment as defined by the drugs themselves, specifically the types, strengths and availability of drugs in the modern world.
We have already seen that humans have a longstanding, rich, varied and well-documented relationship with drugs, but what becomes clear from the study of the history of drug taking is that our ancestors had shocking limitations of opportunity compared to the modern human. The drugs most associated with addiction, harm and problems in the modern world simply weren’t available to our ancestors. Consider cocaine. It is widely known that indigenous peoples of the Andes mountains have long chewed on or brewed tea from the leaves of plants in the genus Erythroxylum, notably Erythroxylum coca, and continue to do so in many areas. Coca leaves contain cocaine and chewing on them gives a number of benefits to users including mild stimulation, suppression of hunger and thirst and some relief from altitude sickness. However, don’t go thinking that your average Andean resident is talking fifteen to the dozen about anything and everything, embarrassing themselves at some middle-class dinner party. The amount of cocaine in coca leaves is very small, coming out somewhere around 0.5 per cent by weight depending on species, variety and location.11 Cocaine as we know it in the modern world is a very different drug altogether.
To get from cocaine in coca leaves to cocaine hydrochloride, the substance we identify as pharmaceutical cocaine, is an involved and labour-intensive process. To start with you need an awful lot of coca leaves. To make a kilogram of cocaine requires half a tonne or more of leaves, which is rather more than the odd bag you might find in an Andean market. Once you have procured your raw ingredient you need to extract the cocaine from it using either solvent extraction (commonly with petrol or kerosene) or acid extraction using sulphuric acid. Both methods require the addition of a number of other chemicals to allow the coca paste to come out of solution, or precipitate. The resulting paste, known as cocaine base, is further worked chemically with hydrochloric acid and physically using hydraulic presses and filters to create cocaine hydrochloride, which can be made into a powder by being heated.12 The resulting powder is typically taken by insufflation, better known as snorting, whereby the powder is inhaled into a nostril via a suitable tube or rolled-up bank note.
Remember, coca leaves contain around 0.5mg of cocaine per 100mg of leaves, and to make a kilogram of cocaine can require anything up to 500kg of coca leaves. Typical doses of cocaine hydrochloride as snorted by an average recreational user are around 50–100mg per dose. Assuming a purity of 50 per cent (street cocaine is increasing in purity and 60–80 per cent is common13) a typical user might intake, in one dose, around 25 to 50mg of cocaine. Now, not all that cocaine is biologically available and there are other factors to consider but already we can see that, in broad-brush terms, you’d have to consume an awful lot of leaves to get even close. Not allowing for any differences in availability or other factors, we are talking about consuming 10g of leaves in a few seconds to get a similar hit. For reference, a decent handful of privet leaves from my back garden, not dissimilar in terms of size and shape to coca leaves, weighs around 10g and eating these quickly would be a struggle. In fact, coca leaves tend to be chewed slowly throughout the day and while some users can end up taking in an impressive 200mg over 24 hours, the concentration of intake is very low and this high level of use is unusual.14 The concentrated, intense and pleasurable hit that cocaine hydrochloride provides is only possible through the conversion of naturally occurring leaves into highly processed powder.
Likewise, the other well-known and highly addictive drug, heroin, is quite far removed from the natural product from which it is manufactured. Opioids derive from opium, the dried latex sap that is exuded from cuts made in immature flowering heads of the opium poppy. The latex contains morphine along with other substances including codeine and thebaine, the substance from which oxycodone and other opioids involved in the US opioid crisis can be manufactured. As with cocaine in coca leaves, we have a long history of opium use dating back more than 6,000 years, with evidence of opium being found from that period at the Cueva de los Murciélagos (the ‘bat cave’) in Andalucía, Spain. Morphine is the most abundant, powerful and important of the substances in opium and it makes up around 10 per cent by weight of the latex. Opium then is a natural product with a long history of human use and with a potent effect. The potency of natural opium pales though when compared first with morphine, extracted from opium in the early 1800s, and then with diamorphine, or heroin, first synthesised from morphine in 1874. Morphine, concentrated from the 10 per cent found in opium, was quickly found to have a much more potent effect and to be more addictive than opium, while heroin (a trade name devised by the chemical company Bayer) is considered around twice as potent again as morphine.
Cocaine and heroin demonstrate an important feature of the drugs environment of the modern world: drugs are much more potent these days than they were. We have refined and developed technological methods to process and concentrate naturally occurring substances to produce powerful drugs, but the increase in drug potency in the modern world can also be seen with a drug that exists in exactly the same form now as was enjoyed by our ancestors. Cannabis, whether in the form of buds and leaves of the Cannabis plant or as the resinous extract that makes hashish, is typically heated or burnt and the smoke inhaled. You can also eat it or brew a tea from it. Whether you chuck it on a fire or develop extravagant bongs and vaporisers to get the smoke into you, the basic scenario is the same as it was thousands of years ago. Cannabis has not, so far, been industrially transformed into a different, widely available product as was the case with coca and opium. What has happened with cannabis, though, is a form of evolution via artificial selection. We have selectively bred varieties of cannabis plant that produce an end-product with dramatically more tetrahydrocannabinol (THC) than is found in the naturally occurring plants available to our ancestors. A large-scale systematic review and meta-analysis of THC content in herbal cannabis (the buds and leaves of the plant) showed an overall increase from around 1–2 per cent in 1970 to 5–9 per cent in 2009, with an overall average increase of 5 per cent. The trend over the next decade was for this increase to accelerate, with cannabis getting stronger at a greater rate in recent years. Some strains of cannabis regularly test with THC concentrations well over 20 per cent15 and the legalisation of cannabis in some parts of the USA has led to the development of cannabis products with very high THC levels.16 The recent cannabis environment is beginning to change in a similar way to cocaine and opium, with technology creating far more potent products. Together with breeding more THC-rich strains of cannabis, it is a development that is concerning many who fear that the increasing use of high-potency cannabis can lead to psychosis, a connection that is far from straightforward but increasingly supported by evidence.17
As well as increasing potency, the drug environment of our recent past has also seen a step change in the range of drugs available to us. We have done more than just improving on drugs that we were already taking; we’ve made completely new ones. A long list of synthesised abused drugs includes amphetamine, methamphetamine (‘crystal meth’), ecstasy, barbiturates, LSD, phencyclidine (PCP, or ‘angel dust’) and ketamine. Meanwhile, globalisation has greatly increased the ease with which drugs can be shipped around the world and the internet provides all kinds of potential for buying and selling. The modern environment is one of great temptation and a wealth of new and potent opportunities to highjack a brain that evolved to enjoy, and reward, the pleasures of sex and ripe berries.
Drunken monkeys
It is a relatively uncontroversial thing to say that a great many people have sex while drunk or at least while under the effects of alcohol. It follows that unless there is some mechanism whereby drunk people can’t conceive, and the problem pages of many magazines strongly suggest this is not the case, many of us were likely conceived through an act of union inspired and facilitated by alcohol. Alcohol lowers inhibitions and can make us, in the short term at least, more socially outgoing. Recent studies also suggest that cannabis use might have positive effects on sexual frequency18 while ecstasy has been shown to increase sexual desire and satisfaction.19 If the alteration of our mental state through the use of drugs could lead to more sex, then could we not put together a plausible evolutionary hypothesis that suggests that, in some way, we may be ‘willing hijackees’ when it comes to taking at least some drugs? When it comes to alcohol, the most used and abused drug of all, the answer is probably yes.
We can construct an evolutionary argument for alcohol imbibition, and the evidence for it, by considering a number of different aspects of alcohol. First, it is easy to make. Fermentation, whereby yeast converts sugars to ethanol, happens naturally and as soon as we started growing crops like barley, wheat, sorghum or rice, then alcohol would have swiftly made an appearance. We didn’t even need crops to make alcohol. Fruit can be gathered and fermented, while milk will ferment to produce kumis, a drink with a history that stretches back at least 7,000 years and an alcohol content of up to 2.5 per cent. The opportunity was there and history suggests we took it.
Second, alcohol makes us feel good and studies indicate that it has an effect on those all-important dopamine reward pathways of the brain.20 We already know that we like to do things that make us feel good. Third, alcoholic drinks, at least in the early days, would have been nutritious and potentially safer to drink than the water available in some locations. Fourth, and most important, in moderate quantities alcohol is a powerful social lubricant. Drinking together would have acted to bond groups more closely, providing huge benefits for activities like hunting and for general social organisation. Of course, addiction to alcohol is a major global health problem and alcohol dependence is so great that sudden withdrawal can cause death, so there is a serious downside to it. However, in our earliest times, when we were adapting to alcohol intake, there weren’t shops on every corner selling high-strength beer, wine and spirits. The alcohol levels, and the availability of alcohol in the environment in which we developed our drinking habits, made that environment very different from the one in which we find ourselves in the modern world.
So far so good, but none of these parts of the story necessarily imply evolutionary adaptation to drinking alcohol. Indeed, evidence that alcohol stimulates the reward pathway leads us rather neatly back to the hijack hypothesis, especially when paired with the nutritional benefits that consuming fermented beverages might confer. If we add in the value of social bonding and our ability to pass on cultural habits, then we need not invoke any further evolutionary argument. However, if we look further back into our evolutionary history we can come up with a very solid evolutionary argument for drinking alcohol. This argument has become known, rather charmingly, as the ‘drunken monkey hypothesis’.
Central to the drunken monkey hypothesis is the fact that ripe and overripe fruits naturally ferment to produce alcohol. Robert Dudley, the proposer of the hypothesis, suggested that our early ancestors, and we are talking 10 million years ago, evolved a genetically based attraction (sensory and behavioural) to ethanol that allowed them to find these nutritionally rich prizes. The odour of ethanol, which carries in the air and could be detected at long range, would have allowed an animal attuned to it to home in on nutritious fruits in forests that might otherwise provide rather slim pickings.
The drunken monkey hypothesis finds support from the evolution of alcohol dehydrogenase (ADH) enzymes that allow us to breakdown the ethanol in alcoholic drinks. A study published in 2014 used the technique of paleogenetics to study the evolution and functioning of a particular type of ADH called ADH4. By looking at the evolution of genetic sequences, paleogenetics is able to ‘resurrect’ proteins from long-extinct ancestors. In this study, the researchers resurrected ADH4 from primate ancestors and showed that a major change happened around 10 million years ago. ADH4 is present in our mouths, oesophagus and stomachs and prior to 10 million years ago was rather poor at breaking down ethanol. The mutated version, on the other hand, is some 40 times better and equipped our ancestors for consuming fermented, alcohol-containing fruit. The timing is interesting too, since it coincides with our ancestors adapting to a life on the forest floor where ripe, overripe and fermented fruits would have been encountered. Also, at this time in Africa forests were shrinking and grasslands expanding. Avoiding open country, where our ancestors would have made an easy lunch for other creatures, would have been important, so an ability to find increasingly scarce fruit in the dwindling forests could have been a strong selection pressure on the evolution of ADH4. The old version of ADH4, incidentally, was very good at metabolising a different alcohol called geraniol as well as alcohols like cinnamyl, coniferyl and anisyl, which are produced by plants to prevent herbivores eating their leaves.21 Our early, arboreal ancestors needed their version of ADH4 for leaf eating, while their descendants found the mutated version perfect for fruit.
The ethanol that ADH4 allowed our early ancestors to consume would have been present in very low concentrations and was, as a direct consequence of how it formed, consumed with food. The consumption of small amounts of alcohol in this way is known to have some health benefits. For example, considering all cancers combined, a study of middle-aged men found that cancer deaths were lower among those consuming up to one drink per day than they were in those who didn’t drink at all.22 Moderate alcohol intake can also protect against strokes that are caused by severely reduced blood flow to the brain (known as ischemic strokes).
The evidence suggests that we evolved an ability to consume alcohol very early in our lineage as a consequence of selection pressure on our diet. The ability to find and consume fermented fruits was an advantage and the small quantities of alcohol concerned may have conferred some health benefits. The interaction with dopamine reward pathways worked to link nutrient-rich and valuable food with pleasure. Much later in our evolution came the development of large-scale deliberate fermentation, following on from the development of agriculture. Deliberate fermentation created an environment of abundant and concentrated alcohol that super-stimulated our reward pathways. To some extent, the reproductive and survival advantages of social lubrication and group bonding that were provided by larger qualities of alcohol would have outstripped the health costs of increased alcohol consumption. Alcoholic drinks would also have travelled relatively well and provided nutrition. Despite these advantages, we were already taking steps towards the modern problems of alcohol abuse by changing our ‘ethanol environment’. The modern world in which we now find ourselves is one in which alcohol is even more concentrated and easily available than ever before, and that makes for a very potent and dangerous evolutionary mismatch.
Risk addiction
So far we’ve dealt with substance abuse and developed a compelling case that our current problems around addiction and dependence are the consequence of a hijacking-mediated mismatch between our evolutionary heritage and the modern world. Does this logic hold up for the other things to which we can become addicted, at least in the everyday usage of the word? It is worth noting that medical acceptance of certain behaviours as ‘proper’ addictions has been slow in developing, although recently behaviours including gambling disorder, internet gaming disorder, internet addiction, food addiction, hypersexuality (‘sex addiction’), shopping addiction, exercise addiction and tanning addiction have become accepted alongside substance addictions. Addictions to sex and food (especially fatty and sugary food) make perfect sense from an evolutionary perspective. Sex is a primary stimulus for the mesolimbic reward pathway and if the opportunity is available to partake in a great deal of it, then it is easy to see how the reinforcement and learning mechanisms we have already met could take over. Food is also a primary stimulus for the reward pathway and fast food in particular provides the sort of calorie-dense feast that, at least in the short term, is highly rewarding. Pornography addiction, which is part of a wider issue concerning the use of pornography in an internet-enabled porn-rich environment, can also be explained through primary stimulation of the mesolimbic pathway, especially if coupled with masturbation and orgasm.
One widely recognised addiction that is of particular interest in an evolutionary sense is addiction to gambling. Often termed ‘problem gambling’, gambling addiction is now classified (by the Diagnostic and Statistical Manual of Mental Disorders 5th edition, or DSM-5) as an addiction and is properly called gambling disorder. Gambling disorder is gambling that causes problems either for the gambler (usually in terms of money and time) or for others (typically the gambler’s family). A need to gamble, a preoccupation with gambling and the gambling of larger amounts of money ever more frequently leads to ‘loss chasing’ (where gamblers gamble harder after losing to recoup their losses), concealment of gambling behaviour, unsuccessful attempts to cut back or give up and symptoms of withdrawal (irritability and restlessness) when unable to gamble. Alcohol abuse is often a related issue and chronic gamblers may end up contemplating or attempting suicide.
Gambling is just that, a gamble, and while some knowledge and skill can mean that gamblers end up on top, the reality is that most do not. Take a look at a fruit machine and you’ll see the payout percentage clearly displayed. The ‘return to player’ as it is called is usually between 80 per cent and 98 per cent, but is typically around 85 per cent. What this means is that if £1,000 is put into the machine the player will receive, on average, £850 back. This is a very poor return in anyone’s book. Of course, you might get lucky and hit the jackpot, but you probably won’t and the ‘return to player’ percentage says that over time you certainly won’t; over time, you’ll lose on average 15 per cent of whatever you feed in.23 Slot machines are games of chance, but games that involve some level of skill (such as some casino card games) can improve the gambler’s chances. Overall though, the odds are always strongly in favour of the house. Horse racing and other sports betting can improve the chances of winning for knowledgeable gamblers, but the continued occurrence of major sporting upsets confirms that there really is no such thing as a ‘sure thing’. Given that gambling is a seemingly highly irrational and damaging behaviour, it is not surprising that a number of studies of gamblers have tried to construct a biochemical framework to understand why people do it and why they can’t stop.
The results of these studies are not always that clear, with suggestions that some gamblers may gamble to increase levels of adrenaline, that gambling may be associated in some way with serotonin, that gambling might be linked with other impulse control disorders, anxiety disorders or personality disorders and, as we might now expect, that gambling causes stimulation of the mesolimbic pathway. One fact that is particularly illuminating when it comes to understanding how the mesolimbic reward pathway might be involved is that people experience a greater dopamine response if they don’t know a reward is coming. The lights and sounds of slot machines especially are thought to enhance the ‘surprise’ of a big win and reinforce the ‘high’ caused by the unexpected dopamine surge.
Understanding the connections between gambling and reward is easier if we think of gambling more generically, as risky behaviour undertaken with the possibility of a large reward. In an ecological setting, taking risks can be highly beneficial in uncertain environments. Imagine for a moment that you are a mouse. All the time you are hiding in your mouse-hole somewhere, you are safe, but what you are not doing is eating or reproducing. Leaving your safe refuge leaves you open to predation, limiting survival, but gives you the opportunity to find food and mates. Understanding the trade-offs between risks and rewards, between costs and benefits, is fundamental to our understanding of the evolution of many behavioural and life-history traits in animals. Indeed, the emerging field of animal personality research, which studies the consistency of individuals’ behaviour, places great emphasis on ‘bold’ and ‘shy’ as personality types and it is risk-taking behaviour that mostly defines these categories. If, under certain circumstances, risks are worth taking and risk-takers secure more resources and more offspring than risk-averse individuals, then it is easy to see how we could have evolved to reward such behaviours. Reinforce that risk-taking tendency with the bells, whistles and lights of the modern world and all its gambling opportunities, and firing up that reward pathway without taking life-threatening risks suddenly seems awfully tempting.
Understanding problem gambling from an evolutionary perspective opens up new treatments. Some suggest that compassion-focused therapies (CFT) provide an approach that allows addicts to understand better why they are in the situation so that they are better able to develop new strategies to manage their behaviour. As John Paulson of the University of Southern Indiana and author of ‘Hardwired for Risk: The Clinical Utility of Exploring Evolutionary Aspects of Gambling’, an article published in the Journal of Gambling Issues in 2018, put it, ‘The hope is that coming to see and appreciate increasingly the influence of evolution on gambling will help those persons suffering to reduce their sense of shame and recover from their struggles.’24
Children in a modern-world sweetshop
Addiction of one form or another is one of the most damaging products of mismatches between our evolution and our current environment. By subverting our evolved reward system, highly destructive drugs and behaviours can become a significant factor in our lives and deaths. However, they can only do this to the extent that they do because of the great increase in ‘potency’ that the modern world provides. For drugs, potency is easy to understand but for other addictions it is no less the case. Fast food is both highly available and high in caloric value; a burger and chips is surely more potent than a basket of roots and berries. We can gamble on our phones, in pubs, in casinos, on computers and via the lottery and the combination of huge wins and accessibility means the gambling environment of the modern world is far more potent (although existentially less risky) than ever before. Overall, the modern world we have created interacts with our evolutionary tendency for chasing dopamine rewards, and the resulting mismatch leaves us as helpless as children in a sweetshop.