Human societies have made and consumed alcohol for millenniums, valuing its mind-altering properties and role in social situations, and have also faced harm from over-consumption. We are far from being the only species on the planet in thrall to alcohol. A recent study by Anna Bowland and colleagues documents the widespread role of alcohol consumption in the natural world.
Ethanol, the familiar alcohol in beer, wine and spirits, is present in many wild fruits, saps and nectars and is consumed by species as diverse as flies and chimpanzees. This alcohol binds together disparate species like yeasts, plants, bacteria, insects and mammals in codependent relationships, with costs and benefits to the partners. It provides both nutritional and non-nutritional values, it is a potential medicine, changes animal behaviour and leads to costly accidents.
Plants produce a wide range of different alcohols, but do not naturally produce the human alcohol of choice – ethanol. Plant-produced alcohols, including methanol, are generally toxic and may be used to kill or deter damaging fungi, bacteria or animals that eat the plant. Ethanol is produced by yeast, a tiny fungus, and may play a role in killing off bacteria that compete with the yeast for the carbohydrates it needs.
Plants evolved sugar-rich fruits to attract animals to disperse their seeds, providing the perfect resource for yeasts. Yeasts break down sugary carbohydrates into ethanol and energy molecules. Many animals evolved the molecular machinery to process and tolerate ethanol, enabling them to get around the worst effects of toxic alcohol levels.
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Humans make and consume particularly concentrated sources of alcohol. Most fruits in nature contain less than one-tenth of the alcohol that you would find in a typical beer, but some have been found to have as much as 10 per cent alcohol by volume, a little less than in a glass of prosecco.
One species that can match us drink for drink, however, is the humble vinegar fly. These are the tiny weak flying insects that you can encounter at an over-ripe fruit bowl. Vinegar flies lay their eggs in fermenting fruit and the maggots do better in high-alcohol environments, ranging in concentration from beer to strong red wine levels.
Much of the information we have on animals in natural environments consuming alcohol is anecdotal, rather than carefully and scientifically documented. We don’t know if the wasps of late summer are so cranky because of their diet of alcoholic fermented fruit. We do have a lot of evidence of animals consuming alcohol given to them purposefully by humans.
The elephant Prince Tom, who travelled the world by ship in the Victorian era before settling in Dublin, developed a well-documented alcohol problem. Waxwing birds were found to have died after a collision with windows and walls, having eaten fermented berries. An unfortunate case of self-harm from drink-flying.
There is variation in alcohol tolerance levels among members of the same species which encounter alcohol at different levels. Honeybee workers, foraging outside the hive on potentially alcoholic plant nectars, have a higher resistance to intoxication than honeybee nurses who stay inside the nest to look after bee larvae. These nurses also lack a key enzyme which enables them to break down alcohol. Fruit and nectar-feeding mammals are more likely to have evolved genes which enable them to break down alcohol and therefore tolerate higher levels of alcohol in their food.
Alcohol has toxic effects in humans as well as other animals, so why do animals consume it? While there are significant costs of alcohol consumption there are potentially some benefits. Ethanol both indicates a high sugar and calorie content in a food source and is an energy source itself. Alcohol can be easy to smell and make foraging for fruit easier. The presence of alcohol in food can also provide a safer resource as it can exclude more damaging bacteria.
A diverse range of species is adapted to consuming alcohol, with evolution contributing to the delicate balance between the benefits and harms of consuming alcohol-rich foods. More information about alcohol consumption and its effects on animals can contribute to a better understanding of our potted evolutionary history with this social lubricant, carcinogen and disinfectant. We do not drink alone.
- Prof Yvonne Buckley is co-director of the Co-Centre for Climate + Biodiversity + Climate at Trinity College Dublin
