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Addictions afflict not only humans but are also observed among animals. In scientific experiments, researchers worldwide study the formation of various dependent states in our "smaller brothers."

It is not only domestic animals living alongside humans that consume alcohol or other substances capable of altering behavior patterns. In some cases, humans themselves may set a bad example by offering their pets alcohol. However, even without human involvement, animals in the wild consume varying amounts of ethanol from fruits, which can constitute the primary diet of some birds, mammals, and insects.

In 2014, neurobiologist K. Olson from Oregon Medical University, along with colleagues, analyzed the songs of "tipsy" zebra finches. The scientists gave the birds juice containing 6.5% alcohol. The authors note that finches, being typical songbirds, learn their unique songs in a manner analogous to how humans acquire speech. During the experiment, the neurobiologists discovered that the birds not only willingly consumed alcohol but also experienced changes in their song structure; after drinking, they literally began to "slur" in parts of their songs, producing an indistinct rhythm and melody. With a significant increase in blood ethanol levels, the finches sang more quietly and with an altered acoustic structure. The scientists observed pronounced effects, including not only a reduction in amplitude but also an increase in song uncertainty, caused by alcohol's disruption of overall rhythm maintenance.

It is noteworthy that changes were observed in the birds' song performance, but no coordination impairments were detected in their general behavior. No general behavioral changes were identified in the zebra finches after "having a drink." That is, they sang "drunkenly" but behaved soberly. This interesting study provided scientists with a deeper understanding of how alcohol affects formed neural circuits in the birds' brains. Another intriguing aspect is that under alcohol's influence, some birds tried to "enunciate the syllables" of their songs more clearly, while others, conversely, became confused in their song's rhythm and "syllables."

Most often, scientists study the effects of alcohol on laboratory rats, domestic animals, and primates. However, there is a nuance: primates and rats lack a vocal apparatus similar to humans, whereas the vocal apparatus in birds and humans functions similarly, both in terms of neural control and complex behavioral responses.

Finch chicks learn complex trills from their fathers (not least because male finches sing more variedly and complexly than females), just as children learn speech from their parents and social environment. The study of "drunken" finch songs may help scientists determine how alcohol affects the neural mechanisms of our speech.

For humans, systematic and uncontrolled alcohol consumption has devastating consequences, but how does it affect animals and insects?

Biologists F. Wince, A. Zitmann, M. A. Lachance, and R. Spannagle observed wild shrews in the tropical forests of Western Malaysia and found that some individuals of these cute, pleasant-looking animals systematically consume the alcoholic nectar from the flower buds of a local palm tree.

This small animal measures 5 – 8 cm in body length and weighs 4–16 grams. The shrew's muzzle is highly elongated and resembles a small trunk. Malaysian shrews are natural pollinators of the bertam palm.

As representatives of their family, shrews are generally beneficial to humans and cause no harm, although they occasionally engage in mischief and may raid beehives to feed on bees. There are about 70 species of shrews in the global fauna, all occupied with their own affairs: some eat insects, others eat worms, and others actively dig in the earth. However, the Malaysian shrews daily consume the alcoholic nectar from the flower buds of the bertam palm. Scientists have recorded a maximum alcohol concentration of 3.8% in the palm nectar. As it turns out, this is the highest concentration of alcohol ever recorded in a natural food product.

This is because a certain amount of yeast thrives in the palm's flower buds, which is why the nectar contains a high level of alcohol. Nevertheless, the shrews that systematically visit the palm flowers show no serious signs of intoxication. These small animals have a high tolerance for alcohol, as the shrew's interaction with the bertam palm is rooted in a long evolutionary process.

An analysis of the shrew's hair showed that the concentration of alcohol in the animal's body is significantly higher than that in a human with an equally high level of alcohol consumption.

Scientists suggest that alcohol consumption, ranging from moderate to high levels, was present in these shrews even in the early stages of their evolution. However, it is not yet clear to what extent the shrews benefit from alcohol consumption or how they mitigate the risk of consistently high blood alcohol levels.

Unlike the Malaysian shrews, which, like the zebra finches, appear composed "under the influence" and show no behavioral signs of intoxication, another animal – the pen – tailed treeshrew – also consumes the nectar of the bertam palm and behaves quite respectably. In fact, the pen – tailed treeshrew is the most prolific drinker among all visitors to the "palm bar." This animal consumes more nectar than other enthusiasts. We can only hypothesize that alcohol might have a positive psychological effect on the animals, but there is no substantial evidence for this.

This unique bar in the Malaysian jungles is regularly visited by gray tree rats and Malaysian rats, as well as the slow loris. The most frequent patrons are the treeshrews and lorises. They spend 86 to 138 minutes on the palm tree every night.

B. Wince, who studied the "bar life" of Malaysian animals, installed surveillance cameras around the palm. During the research, no serious behavioral changes were ever recorded in the "drinking" animals.

Unfortunately, such resistance to alcohol was not passed on to humans in the evolutionary process; we can only envy the Malaysian treeshrews and shrews—they can drink without getting drunk.

R. Dudley, a biologist from the University of California, Berkeley, studied the mechanism of human attraction to alcohol for about 25 years. In his 2014 book, The Drunken Monkey: Why We Drink and Abuse Alcohol, he proposed the hypothesis that the attraction to alcohol began to form in our primate ancestors, who heuristically discovered that the smell of ethanol could lead them to ripe fruit. Studying monkey behavior, R. Dudley identified a pattern: the animals seek out fruits that are ripe enough for their sugars to have fermented. During this fermentation, the fruit juice develops about 2% alcohol, and the monkeys eagerly consume such fermented fruits.

Primatologists C. Campbell and V. Weaver from California State University, Northridge, collected partially eaten fruits discarded by spider monkeys living in Panama and found 1–2% alcohol in them, a byproduct of natural yeast fermentation. Analysis of the monkeys' urine revealed that it contained secondary metabolites of alcohol. The researchers concluded that the animals used fermented fruits for energy.

Subsequently, C. Campbell, together with R. Dudley and A. Maro, studied the diet of chimpanzees in Uganda to test R. Dudley's "drunken monkey" hypothesis. Observations confirmed the presence of ethanol in their food, and a certain amount of alcohol was also detected in the chimpanzees' urine. However, no serious behavioral or physiological consequences from consuming overripe fruit were identified. The fruits preferred by the monkeys contained an alcohol concentration equivalent to that of weak beer or cider. The fruits of the jobo tree are one such example.

C. Campbell suggested that monkeys obtain more calories from fermented fruits than from unfermented ones, and more calories mean more energy. The scientists concluded that the fruit selection priority of human ancestors was similar; they preferred fruits saturated with ethanol because they provided more energy to the body.

However, researcher C. Milton expressed skepticism about biologist R. Dudley's hypothesis and published a critique of his study in the journal Integrative and Comparative Biology. In her article, C. Milton argues that ethanol is more likely to repel primates than to attract them. She states that when fruits contain higher levels of ethanol, both humans and other primates avoid consuming them, using smell as a guide. C. Milton notes skeptically that there is no benefit from ethanol; it is merely a pleasant toxin. She proposed her own theory for the human attraction to ethanol, the essence of which is that humans lack the innate wisdom regarding dietary habits, unlike primates. Human culture has been fermenting alcohol for millennia, and as a result, through the experience of previous generations, people have learned to appreciate it. According to C. Milton, the reason for this human attraction to alcohol has nothing to do with nutrition or health; people are drawn to any substance capable of altering their consciousness.

If the situation with primates is more or less clear, the case with African elephants remains less straightforward to this day. In 2006, scientists S. Morris, D. Humphries, and D. Reynolds set out to debunk the myth of the drunken elephants of Southern Africa. Africa is an exotic continent with various intricate, whimsical folklore stories, and the tale of drunken wild elephants is one of them. The suggestion that the African elephant gets drunk by eating the fruit of the marula tree is a fun story for tourists, the press, and even scientific works. According to S. Morris, an elephant might occasionally eat marula fruits, but there is no clear evidence of elephants becoming intoxicated in the wild. Based on calculations using human physiology for comparison, a 3,000 kg elephant would need to consume approximately 10–27 liters of 7% ethanol to reach a state of behavioral change.

Marula fruits contain about 3% ethanol. An elephant, which typically has a varied diet, would obtain an average of 0.3 g/kg from these fruits, which is half the amount required for intoxication. Thus, the hypothesis that elephants get "drunk" from gorging on marula fruits remains unconfirmed.

However, this myth has troubled scientists for many years. In 2023, researchers from Botswana decided to follow S. Morris and his colleagues in attempting to dispel the myth of African wild elephants in Southern Africa becoming intoxicated from marula fruits. T. Makopa and G. Modikwe, along with other researchers, collected marula fruits from an area exceeding 800 km² in Botswana and isolated about 160 yeast strains from them. Approximately 93% of these isolates typically ferment simple sugars and produce ethanol. The ethanol content in the marula fruits suggested it could potentially influence elephant behavior in the wild if consumed in large quantities. However, data from a single study proved insufficient to refute the myth of drunken elephants. The notion that elephants become drunk and behave badly after gorging on marula fruits remains unproven and continues to be propagated in modern South African folklore. While the case of the elephants remains unclear, the situation with honeybees is better understood.

American scientists I. Ahmed, C. Abramson, and I. Faruq observed that honeybees hovering near an ethanol source, or even their fleeting flight past it, can cause kinematic changes in the bee's body and wings.

To capture significant changes in the body and wing movements of honeybees under the influence of ethanol vapors, the scientists used four high-speed cameras (9000 frames/sec). Using statistical analysis tools, the observers investigated kinematic changes in the bees' bodies and wings caused by exposure to increasing ethanol concentrations from 0% to 5%. The bees exhibited a changed body roll angle, a decreased wingbeat frequency, and an increased wingbeat amplitude. However, the researchers did not specify the cause: were the bees becoming intoxicated, or was it related to other factors?

Back in 2006, Slovenian scientist J. Božič, while studying the behavior of intoxicated bees with a team of other researchers, noted a correlation between increased ethanol levels in the bee's body and changes in behavioral responses. J. Božič, along with colleagues C. Abramson and M. Bedenčič, trained honeybees to visit feeders containing sucrose and 1 – 10% ethanol. Observing the behavior of the "drunken" bees, the scientists discovered impairments in their behavioral acts within the hive.

Communication among bees occurs through a specific set of movements, a kind of dance, through which they convey information to each other. When consuming alcohol, the bees showed reduced activity in waggle dances and an increased frequency of tremble dances. The "drunken" bees also engaged in food exchange more frequently than their sober counterparts and performed body cleaning rituals somewhat more often. The changes in honeybee behavior under ethanol reflect the alcohol's impact on their nervous system. Similar behavior occurs in insects poisoned by sublethal doses of insecticides.

In 2018, K. Miller, K. Kushevska, and V. Privalova, in their study on the effects of ethanol on honeybees, revealed features of adaptive responses in the insects.

The honeybee is often used by scientists as a simple invertebrate model for alcohol-related research. To date, several consequences of consumption have been demonstrated in honeybees, but tolerance to ethanol consumption as a sign of alcohol abuse had not been demonstrated in scientific experiments for a long time.

Polish scientists confirmed the hypothesis that the motor impairment response to ethanol is lower in bees that have previously experienced its effects. Bees exposed to alcohol for the first time more clearly demonstrated intoxication, expressed in movement disorders. The data led the scientists to conclude that bees over time acquire resistance to the effects of alcohol, which could hypothetically be a sign of alcohol abuse. Theoretically, if we transpose bee behavior to human behavior, could bees with increasing tolerance to alcohol subsequently become dependent?

The culmination of the story of bees under the influence of alcohol is the research by Polish scientists M. Ostap – Chek, M. Opalek, D. Stek, and K. Miller, which showed that bees do, in fact, exhibit signs of a hangover.

M. Ostap – Chek and colleagues investigated the characteristics of alcoholism in honeybees and observed manifestations of withdrawal syndrome in the insects. In worker bees that had long-term consumed food supplemented with alcohol, pronounced seeking behavior and a clear striving for immediate ethanol consumption were observed after access was discontinued. The researchers also noted a slight increase in mortality among the bees as a result of withdrawal and subsequent access to alcohol.

In the human world, seeking behavior is observed when a person dependent on alcohol, drugs, or a behavioral addiction searches for an opportunity to use consciousness – altering substances or ways to satisfy their need. For instance, a drug – dependent person starts contacting people who potentially use or know where to obtain illicit substances. Driven by the seeking motive, the person strives to meet with other substance users and seeks opportunities to use them.

But let's return to the bee study. The results of M. Ostap – Chek and his colleagues' research showed that not only do bees develop alcohol dependence, but they may even experience a hangover syndrome.

Another team of Polish researchers, led by J. Korczyńska and A. Szczuka, studied the influence of ethanol and acetic acid on the behavior of worker narrow – headed ants in 2023. The experiment studied the behavior of worker ants. For a set period, one group of ants was placed near cotton pads soaked with water, another near a pad saturated with an aqueous ethanol solution, and a third near a pad soaked in acetic acid. The researchers conducted 30 simultaneous five-minute tests for each group.

According to the scientists' observations, ethanol and acetic acid caused significant changes in the insects' movements and affected their exploratory behavior, grooming rituals, and level of aggression during interactions with nestmates. Ants near the cotton pad soaked in acetic acid demonstrated aversive behavior, while the group near the pad saturated with ethanol showed enhanced exploratory behavior; under ethanol's influence, the ants began to bustle about.

In the wild, without human intervention, there is another interesting example of how ants come under the influence of a behavior – altering chemical substance.

A 2015 scientific article by Japanese biologists described interesting relationships between caterpillars of the subfamily Lycaenidae and ants. There are about 5,200 species of Lycaenid butterflies in the world, predominantly living in the tropics, but about 450 – 500 species have perfectly adapted to live in the planet's northern regions.

Lycaenid butterfly caterpillars have adapted through evolution to cohabit with ants. Lycaenids found in Indonesia, Japan, Taiwan, South Korea, and North Korea are representative myrmecophilous butterflies.

Myrmecophily is a strategy whereby living organisms exist within or near ant nests. Thus, myrmecophiles are animals or insects that live in association with ants and depend on them for a certain period.

The Lycaenid caterpillar living in Japan secretes a fluid containing sweet substances that attract ants. The caterpillars possess a special dorsal nectary organ that produces this secretion, which contains neuroregulators that compel the ants to remain at their "guard post" nearby and provide protection. The ants consume this secretion, and the neuroregulators within it affect their reward system. In this way, the caterpillar ensures the ants' loyalty and protection – a natural mechanism of "zombification." An ant, having become dependent under the influence of the secretion, never returns to its colony and transforms into the caterpillar's guardian, defending it from spiders and parasites. Incidentally, the relationship between aphids and ants operates on a similar principle; aphids also reward ants. Ants protect aphid colonies from ladybugs and lacewings and move their charges to more succulent young plants. In return, the aphids provide the ants with metabolic sugar, serving as another example of mutually beneficial interdependence in the insect world.

Dependent behavior related to ethanol has even been observed in nematodes. C. Salim, E. C. Kane, and E. Baishan – research fellows in the Department of Pharmacology and Toxicology at the University of Tennessee Health Science Center (USA) – studied the compulsivity of alcohol – seeking behavior in soil-dwelling nematodes in 2022. Under the influence of certain neuropeptides, these roundworms demonstrate compulsive alcohol-seeking behavior and persistently continue their attempts. However, when influenced by other neuropeptides, they exhibit a sustained aversion to alcohol consumption. Perhaps through deeper study of neuropeptide regulation in animal models, scientists can learn to induce a similar aversion to alcohol consumption in humans.

A significant number of studies on the effects of alcohol and narcotic substances are conducted using rodents. In 2004, researchers at the Charleston Alcohol Research Center in South Carolina (USA) specifically trained male laboratory mice to drink alcohol (15% ethanol) for two hours daily.

During the experiments, the mice had constant access to food and water. Once a stable baseline level of alcohol consumption was established, the mice were subjected to 16 – hour periods of alcohol vapor inhalation interspersed with 8-hour withdrawal periods. This cycle was repeated four times, followed by a 32 – hour period. After the final ethanol exposure, all mice were observed and tested for alcohol consumption under limited access conditions for five consecutive days. Subsequently, the animals received a second series of ethanol exposure with withdrawal periods, followed by another five – day behavioral assessment period. What was the outcome of this experiment?

Following repeated cycles of chronic alcohol exposure and withdrawal, ethanol consumption in the mice increased significantly compared to control groups, which were not subjected to any interventions and lived without alcohol.

The alcohol – trained mice subsequently exhibited pronounced seeking behavior and voluntarily consumed ethanol when offered. Consequently, alcohol dependency with characteristic withdrawal syndromes was artificially induced in the mice.

In the wild, there are various instances of animals consuming substances, mushrooms, berries, or plants that would typically cause death or poisoning in humans. In 2021, K. Suetsugu and K. Gomi from Japan's Kobe University noted that local Japanese squirrels safely consume poisonous fly agaric and death cap mushrooms. These mushrooms play important roles in maintaining forest ecosystems. Fly agaric is known for the toxic properties of its hallucinogenic components, such as ibotenic acid, muscimol, and muscarine. Serious cases of fly agaric poisoning in humans can include delirium, hallucinations, convulsions, and sometimes fatal outcomes.

A typical symptom of fly agaric poisoning is the visual distortion of object sizes. Now, raise your hands if you have read Lewis Carroll's fairy tale Alice's Adventures in Wonderland? (If you haven't, I recommend it.)

Remember the episode of Alice's meeting with the Caterpillar, sitting on a mushroom cap, lazily smoking a hookah?

All these manipulations with pieces of the mushroom in the tale, leading to changes in size, are nothing other than the effect of poisonous substances, possibly from the fly agaric, on human consciousness.

However, the Japanese squirrels that consume poisonous fly agarics not only remain unharmed but also show no behavioral signs of intoxication. The squirrels have adapted to eat poisonous fungi, though the reason remains unknown. Scientists hypothesize that the squirrels may act as carriers of fungal spores to new habitats, and to test this, K. Suetsugu plans to study squirrel droppings.

Unlike the Japanese squirrels, dogs in Kentucky have been far less fortunate. In 2019, the Journal of Veterinary Diagnostic Investigation published a case by M. Romano, H. Doan, and R. Poppenga describing a fatal outcome in a domestic Labrador Retriever due to fly agaric poisoning. Confirming mushroom poisoning in dogs can be challenging in veterinary practice. Ingestion is often unobserved, and clinical manifestations are non – specific and could be attributed to numerous other causes. This case was diagnosed using a PCR test. The veterinarians did everything possible but could not save the dog. This is not an isolated incident of fly agaric poisoning in domestic dogs.

M. Romano and colleagues suggested that dogs might be attracted by the fly agaric's distinctive fish – like odor. Thus, what is permissible for Japanese squirrels is clearly unacceptable for domestic dogs in Kentucky.

The illicit consumption of narcotic substances has large – scale negative consequences for human society worldwide and unexpectedly contributes to polluting aquatic ecosystems through wastewater. A study by Czech scientists led by P. Horký, R. Grabic, and K. Grabicová identified the negative impact of methamphetamine contamination in water on brown trout behavior.

The researchers obtained results demonstrating that methamphetamine, a global threat to human health, when introduced into freshwater ecosystems, significantly affects trout motor behavior and induces methamphetamine preference during withdrawal. The Czech team conducted their experiment under controlled laboratory conditions and did not release methamphetamine into natural rivers or water bodies. The fish used in the study, housed in special incubation tanks, were acquired from a local supplier with documentation confirming they were healthy and disease-free.

In total, scientists observed the behavior of 120 fish divided into two equal groups of 60. One group was exposed to methamphetamine dissolved in their tank water for eight weeks. Every other day, researchers replaced two – thirds of the water volume in this tank.

The remaining 60 trout served as a control group, living undisturbed in their tank without methamphetamine exposure. When deprived of methamphetamine, the exposed trout exhibited characteristic drug-seeking behavior. Drawing parallels to human addiction models, where withdrawal symptoms include increased anxiety and stress, the scientists noted reduced movement in trout – interpreted as a stress symptom related to methamphetamine withdrawal. In a similar 2017 study, G. Bosse and R. Peterson observed a "depressed" state in trout during methamphetamine withdrawal, which they also interpreted as withdrawal syndrome.

Why are some animals susceptible to psychoactive substances while others show no behavioral changes or desire to consume behavior – altering substances?

This question was investigated in a 2020 study by Canadian researchers: M. Janiak, S. Pinto, G. Daichaeve, M. Carrigan, and A. Melin.

The team presents genetic evidence for differences in ethanol metabolism among mammals. Some animals possess the ADH7 gene, which enhances metabolic protection against intoxication. This gene increases the efficiency of ethanol – processing enzymes in some mammals by 40 – fold. Thanks to ADH7, shrews can safely consume doses of fermented bertam palm nectar that would be toxic to humans, showing no signs of intoxication. While some animal species can consume alcohol and psychoactive substances in fruits, mushrooms, and plants without significant harm, humans often struggle with these substances, and systematic use leads to dependency.

Despite extensive research in biology, evolutionary psychology, and other interdisciplinary sciences, the effects of alcohol, narcotics, and various toxins on insects, mammals, and fish remain inadequately studied.

Human understanding of these processes also remains incomplete, with ongoing debates among scientists and clinicians. For instance, neuroscientist M. Lewis questions the conceptualization of addiction as a disease.

The disease model characterizes addiction as a brain pathology, supported by evidence of alterations in brain systems governing behavioral control and delayed gratification. This model is grounded in biological data. Within this framework, researchers have analyzed genetic variations and factors predisposing humans to psychoactive substance use, impulsive buying, and other addictive behavioral patterns.

But what if we view addiction not through the lens of disease, but through the perspective of personal choice? What if addictive behavior is, first and foremost, a conscious choice made by the individual? Why does a person choose dependence? What motivates them to make decisions that lead to self – destructive behavior? This perspective is also complex; the concept of choice is certainly more intriguing than the disease model. At the very least, the choice model offers hope that decisions can be different and that a person's patterns of behavior and thought can be changed. In contrast, the disease model appears to remove an individual's responsibility for their decisions, giving them the benefit of being "sick" and implying it is not truly their fault. The thinking becomes, "It just happened; there's medicine and research, so perhaps they can help me get rid of this addiction as if it were a disease."

As the author of this book, I find a comprehensive approach to the causes of addiction more compelling. Ultimately, both external circumstances and internal personal factors play a role. Dependency can be influenced by an adverse environment, stress, high anxiety, an inability to assume responsibility, and a lack of specific resistance skills. But people are not animals; we possess consciousness and have choice. We can make decisions. And we make them, ultimately, in favor of either addiction or self – preservation.