Why do humans drink alcohol? Not implausibly, it has something to do with their primordial fruit-eating heritage: the scent of spontaneously fermented ethanol guided humankind’s ancient arboreal ancestors to the ripest and most sugar-laden fruit in the tree. So we were pleased to obtain a bottle of inexpensive wine from New Zealand whose label made due obeisance to the primate that had inspired this “drunken monkey” hypothesis. True, the Sauvignon blanc grape and howler monkeys have no specific affinity, but the wine itself was amazingly drinkable, with all the extroverted grassiness and grapefruit finish one might expect from the grape and the place. We think the monkey would have approved.
At this point, it might be relevant to pause for a moment to consider why human beings are so fond of wine and other alcoholic beverages. Actually, humans are far from alone in their predilection, and, conveniently, naturally occurring ethanol, the kind of alcohol found in wine, occurs widely in the environment. Indeed, it is found anywhere plants produce sugars. Honey aside, the best concentrated source of sugars is fruit, and once the flowering plants began to diversify late in the age of dinosaurs, well over a hundred million years ago, fruit rapidly became available almost everywhere vegetation could grow. Large numbers of different animals began to specialize in fruit consumption, and at the same time other organisms began to colonize fruit as an environment for sustaining life. Prime among these latter were the yeasts, tiny single-celled fungi that we’ll consider in detail in Chapters 5 and 6. Yeasts today implement fermentation of fruit sugars to produce ethanol, and it has been suggested that their ancestors began doing so as a way of discouraging other microorganisms from competing for the living space and sugars offered by the skins of oozing fruit. Because alcohol is toxic to many organisms, this explanation appears plausible; and in any event the natural fermentation of sugars by yeasts has become ubiquitous. Most of the time the concentrations of alcohol produced spontaneously by yeasts remain pretty low, but the phenomenon is widespread enough to help account for the fact that many different kinds of organism, particularly fruit-eating ones, possess the capacity to detoxify alcohol in small doses.
Some organisms, including humans, seem to benefit from consuming moderate quantities of alcohol. When scientists exposed fruit flies to vapors containing low, moderate, and high concentrations of ethanol, for example, the “moderate drinkers” lived longer and had more offspring than the abstainers. Why this was so is not clear, but it is well established that the scent of ethanol is an important factor in guiding flies toward sources of fruit, meaning that alcohol plays an important role in their economic lives—and in other aspects of their existences, too: fruit fly larvae plagued by parasites medicate themselves by seeking out ethanol-containing foods, and the scientists who observed this phenomenon suggested that alcohol might have a similarly protective effect in other organisms as well. Even if the alcohol did not save their lives, it might have at least cheered the afflicted flies up: another group of scientists reported in 1977 that male fruit flies deprived of the opportunity to mate showed a stronger preference for ethanol than their more successful counterparts.
The key here is quantity. In fruit flies, large quantities of alcohol negate the benefits of small ones, illustrating a common phenomenon known as hormesis, whereby substances that are toxic to animals in large doses can have favorable or agreeable effects in small ones. Hormesis is widespread in nature; and although scientists still debate how it works, one idea is that low levels of many toxins activate physiological repair mechanisms in the body that have broader effects than simply responding to the toxin. Another suggestion is that toxins in low concentration may promote antioxidant effects in the body. Whatever the case, alcohol does seem to have certain favorable effects on humans when taken in moderation, as attested by a substantial literature on the health benefits of drinking wine.
Despite such intriguing discoveries, though, how widely any health benefits of alcohol consumption are enjoyed in the animal world is not known. It is clear that some mammals simply like the stuff, which is hardly surprising, because elevated blood-alcohol levels appear to enhance the production of epinephrine (adrenaline), a hormone that acts in the brain to reduce inhibitions. Thus elephants in parts of southern Africa have long been famous for excessively indulging in the naturally fermenting fruit of the amarula tree, weaving away rather unsteadily after each episode. But as with most other mammals that occasionally go in for such overripe fruit while it is still on or around the tree, this is a strictly seasonal predilection for elephants, limited to the short periods of the year during which the alcoholic fruit is available. Heavy “drinking” is hardly a way of life for them.
More remarkable, then, is the case of the tiny pen-tailed tree shrews of Malaysia. They are particularly instructive in a consideration of why human beings like alcohol because they are widely reckoned to be among the closest living relatives of the primates, the zoological group to which our species Homo sapiens belongs. They may not be precisely the same as our ancient ancestors from the beginning of the age of mammals some sixty-five million years ago, but in appearance, body size, and general habits they probably come close.
In 2008 German researchers reported the results of an ecological study of pen-tailed tree shrews in a western Malaysian rainforest. They noted that the little creatures, under 50 grams in weight, returned repeatedly to feed on the large flowers of the trunkless bertam palm, an abundant plant of the forest floor. Throughout the year, for prolonged periods of time, these flowers exude nectar to attract pollinators. Frothing and bubbling, along with “brewery-like” odors, indicate that the nectar is colonized by natural yeasts and begins to ferment virtually as soon as it is produced. The resulting alcohol concentration in the nectar is as high as 3.8 percent, about as strong as most of the beer traditionally sold in the United States. During the course of the study several species of mammal visited the bertam palms each night in search of this resource, including our primate relative the slow loris; but the pen-tailed tree-shrew beat them all in its enthusiasm for the nectar, sometimes spending well over two hours per night bingeing on this delicacy. Oddest of all, the tiny creatures never seemed to get drunk—even when, relative to their body size, they had imbibed enough to cause a large man to pass out from inebriation. Elevated alcohol levels were detectable in the tree shrews’ blood, but the tiny mammals showed no physiological impairment—fortunately, since these vulnerable creatures are under constant threat of predation. Their senses have to be keenly attuned to danger at all times, and their reactions have to be swift. It is clear, purely from the time spent feeding, that the palm nectar is an important nutritional resource for the tree shrews at the Malaysian study site—as indeed beer, which is actually more nutritious than bread, can sometimes be for humans. But if the tiny quaffers had lacked appropriate mechanisms for counteracting the physiological effects that alcohol has in us, they would have been in deep trouble.
Pen-tailed tree shrew at the bertam palm bar
The example of the tree shrews suggests, at the least, that from the beginning of primate history there may have been both an occasional predilection for the products of fermentation and a mechanism for processing alcohol. Humans exhibit this primate heritage in their physiology: by some reckonings, about a tenth of the human liver’s processing capacity is slanted toward breaking down alcohol via production of such enzymes as alcohol dehydrogenases. Scientists often marvel at this huge apparent dedication of resources to one specialized task, although in fact the alcohol breakdown apparatus benefits from a fortuitous resemblance between ethanol and other molecules which are more routinely encountered.
There are also differences of scale at work here. Although a tiny tree shrew can slake its thirst for alcohol by licking palm-tree flowers, this is hardly a viable solution for human beings, with well over a thousand times more body mass. Naturally occurring sources of alcohol hardly fill the bill, which is why it is more likely that, from the time when they first gained the intellectual and technological wherewithal to figure out how to do it, humans have been devoted to the artificial production of alcoholic beverages.
It is of course a long way, evolutionarily speaking, from tree shrews to Homo sapiens; but we have larger and closer relatives that also share our alcoholic proclivities. Howler monkeys in Central America are much bigger than tree shrews (they can weigh up to 9 kilograms) and have been seen to feed frenetically on the gaudy orange fruits of the Astrocaryum palm. In the best-known case, the sheer exuberant enthusiasm of a particular howler in a forest in Panama aroused scientists’ suspicions that it might be drunk. These suspicions were quickly confirmed. Combined with the observed quantity of the orange delicacies consumed, analysis of alcohol in partially eaten fruit the monkey had let fall from the tree showed that he had consumed the equivalent of ten bar drinks in a single session. No wonder he was tipsy by the end of his feast! And although the scientists observing him reported no immediate adverse physical consequences—he did not fall out of the tree, at least—they did not check him for a hangover.
Observation of the happy howler fit in neatly with the “drunken monkey” hypothesis that the biologist Robert Dudley developed early in the twenty-first century as an evolutionary explanation of the human predilection for alcohol. Dudley pointed out that our heritage is a fruit-eating one. Almost certainly, the first primates were frugivores, and although some of our early relatives soon moved on to leaves and other nonfruit plant parts, the hominoid (ape/human) group from which we emerged some seven million years ago had clearly stayed on the fruit-eating path. Ethanol “plumes” emanating from fruit can be as useful to keen-nosed primates for locating sources of food as they are to fruit flies, and Dudley suggested that early fruit-eating monkeys and hominoids were attracted to ripe fruit by alcoholic aromas.
The plausibility of this scenario was reinforced by the demonstration in 2004 that the presence of ethanol is a better indicator of how much sugar a particular piece of fruit contains than its color is. Even more important, once they have started eating fermenting fruit, the feeders are rewarded by a further energetic premium: unusually for an addictive substance, the caloric value of ethanol is high. Its calorie count is, in fact, almost double that of carbohydrates, as every beer belly in the world attests (if there were no beer around, doubtless we’d be calling them wine bellies). So the idea here is that a variety of circumstances would have conspired to make alcohol attractive to our hungry fruit-eating ancestors, and this predilection was passed down to their descendants today.
The “evolutionary hangover” hypothesis is attractive, but it has some difficulties when applied specifically to humans. A special aspect of the evolution of our own African ancestors was that when they began to venture out of the forests and into woodland and tree savanna environments several million years ago, they changed their diet significantly. Chimpanzees roaming through comparably open areas today largely ignore the new sources of sustenance potentially available to them, and stick to a diet mainly consisting of fruit and leaves, the forest resources with which they are familiar. In contrast, our own hominid ancestors became the ultimate omnivores, reducing their intake of fruit and adding foods such as bulbs, tubers, and animal proteins to their menu. Our ancestral break with the forests thus involved abandoning fruit as the dietary mainstay. Additionally, in sharp contrast to that Panamanian howler, even in the forests many monkeys and apes have been observed actively avoiding the overripe fruits in which ethanol concentrations are highest. As a result, it is impossible to generalize about whether frugivorous higher primates as a whole like alcohol. Some do, and they evidently enjoy not only the valuable information it gives them about fruit quality, but also its behavioral effects.
From a human perspective, one of the most important implications of our descent from an ultimately fruit-eating stock is that our ancient ancestors would inevitably have been routinely exposed to a low alcohol concentration in their diet, whether they actually sought it or not. Such sustained—if muted—ancestral exposure may partly explain how modern humans have come by their modest physiological ability to detoxify alcohol, although a fortunate molecular coincidence is also involved. There is, of course, a limit to how much alcohol various animals can handle, and gram for gram tree shrews have an unusually high tolerance. But humans are remarkably unlike the hedgehog that is reported to have expired from drinking egg liqueur when the alcohol concentration in its blood had not reached even half the legal limit at the time for driving in New York State, and molecular scientists now think they know why. Apparently, a tiny DNA change in the last common ancestor of modern apes and humans resulted in the production of an enzyme that is super-efficient in breaking down the ethanol molecule. In light of this finding, it is perhaps less surprising that humans are attracted to ethanol than that apes do not more actively seek out fermenting fruit. But in any event, once Homo sapiens had acquired its creative bent, this unusual new genetic propensity gave our species an edge in employing fermentation as an economic tool.
Ever since people took up settled existences and could no longer follow animals or plants around the landscape to where they were grazing or producing fruit or seeds at different times of year, they have faced the problem of how to store perishable food. Even with the best agricultural practices, a single fixed location will almost never be equally productive at all seasons. But keeping food around is hardly simple. Stored food rapidly rots through oxidation and other chemical processes, and it is also subject to the depredations of such pests as insects and rodents.
All settled humans thus require means of actively preserving food, and fermentation was probably widely recruited for this purpose by Neolithic people. The zoologist Douglas Levey has pointed out that from an anthropological point of view deliberate fermentation can best be seen as “controlled spoilage.” Most microbes responsible for the decomposition of food cannot persist even in moderate concentrations of alcohol, so by permitting limited alcohol production in stored foodstuffs via controlled exposure to oxygen, Neolithic farmers were able to preserve much of the nutritional value of their crops, even if not their freshness.
For the record, though, fermentation is not the first form of food preservation documented. In the latest part of the last Ice Age, about fourteen thousand years ago, ingenious inhabitants of the icy Central European Plain were already storing meat in deep pits dug in the permafrost to create year-round refrigerators. In the balmy Neolithic Near East this technology was obviously not an option, although drying foods in the sun was doubtless another major approach to the preservation of foodstuffs, and would have provided an obvious solution in many cases. Still, fermentation was clearly important enough to Neolithic farmers as a food-preservation strategy for Levey to suggest that the process was initially adopted for this purpose, to be used only later in producing alcoholic beverages.
Members of our symbolically reasoning species mentally process information about themselves and about the world around them in a novel way. The results are remarkable. But we are unperfected creatures nonetheless; and behaviorally we are still bound by what statisticians call the normal distribution. Otherwise known as the bell curve, the normal distribution simply acknowledges that most people are broadly similar in behavioral and physiological expressions, and deviations from the average become increasingly rare toward the extremes. Most people behave reasonably decently toward one another, for example, while both the saintly and the monstrous are fortunately few. The same goes for the spectrum that lies between being teetotal and a heavy drinker, which explains why the abstemious and the alcoholic make up only minorities of the population. What is more, among humans both unwholesome social pressures and principled beliefs tend to exaggerate behavioral tendencies, as witness Saturday-night binge drinkers on the one hand, and temperance campaigners on the other. But the underlying pattern remains basically constant, and a quick look at the natural world makes it obvious that Homo sapiens is not the only species with a moderate tolerance for alcohol that also overindulges occasionally.
The big difference in our case, of course, is that Homo sapiens has devised means of producing abundant alcohol at will. Combine this ability with alcohol’s addictive and disinhibiting properties, and it seems inevitable not only that some individuals will overconsume but also that this behavior will be recognized as a social evil. Virtually every human society has consequently produced strict rules to govern alcohol consumption, and given our species’ predilection for taking any good idea to its illogical extreme, such rules have not infrequently been compulsively developed into rituals. Innumerable laws, traditions, and proscriptions may regulate the production, distribution, and consumption of alcohol. Yet at the same time, attitudes toward wine can vary within the same culture and even the same individual (humans are famously cognitively dissonant), ranging from seeing it as “the Devil’s potion” to the “blood of Christ.” This is why it is so easy to believe that the products of the winery at Areni-1 were both produced and consumed according to strictly conventionalized and rather compulsive procedures. And why conflicted attitudes toward wine and other alcoholic beverages have reigned ever since.
