This morning, I’m perusing articles on the origin of humanity’s favourite stimulant, sitting— obviously —with a coffee in hand.
Dozens of plant species, across unrelated families, produce caffeine. This indicates it has evolved separately, many times. That seems surprising, but according to Huang et al. (2016), it really isn’t. Plants synthesize caffeine in different ways, but each start with a 100-million-year lineage of enzymes conserved for crucial but unrelated biochemical purposes. Co-opting these enzymes to synthesize caffeine is, therefore, always an ongoing possibility. If all caffeine-producing species went extinct, we can imagine caffeine would likely again evolve.
I find that strangely consoling, perhaps due in equal measure to my joint addictions to both caffeine and to evolution. But what makes caffeine so valuable that it has repeatedly emerged? After all, producing it, like any metabolite, has costs. What kind of selection pressures would pull its synthesis, again and again, from mere possibility into actuality? Independent evolution suggests caffeine synthesis may have different roles in different contexts. There are two favoured theories associating caffeine with a plant’s defense system. One is that caffeine’s antifeeding and pesticidal properties protects it against herbivory. The other is that the release of caffeine into the soil inhibits germination of nearby seeds, reducing competition from neighbours. From my own experience with caffeine, I know its pleasant lift can quickly go awry, so it’s no shock that it would be detrimental to other creatures. I also know the slide from elation to irritation is dose dependent. Could a small hit have positive effects for any other animals? Perhaps even for those very insects— and competing plants —it seeks to debilitate?
Some ingenious experiments on bees shed light on this question. In a story all too convenient for punsters across the world, it turns out caffeine gives bees ‘a buzz.’ Bees on caffeine become more energetic and are more likely to remember the location of caffeinated nectar in complex environments (Wright et al. 2013). This is totally remarkable. According to Evogeneao’s Tree of Life Explorer, humans and bees’ closest ancestors are simple blob-like entities that lived about 630 million years ago. Could it be that virtually all of the species between us and bees, and even that blob, can get high on this stuff? Or is the response to caffeine similar to caffeine itself— evolvable should a species be lucky enough to land in situations where its own endogenous possibility for botanical exhilaration strums into existence?
As I look further, it seems a whole range of insects and molluscs fall for effects Homo sapiens know only too well: they get hyperactive on caffeine, but succumb to tremors and lose their appetite and their focus on larger doses (ex. Nathanson 1984). Mustard’s (2013) review of studies administering caffeine to insects, molluscs and mammals concluded its effect on behaviour is conserved across animal species. Meanwhile, at least one study sees this pattern repeat in another kingdom entirely. A small dose of caffeine stimulates the growth of sunflower plants, but inhibits it at larger concentrations (Kursheed et al. 2009). Indeed, cases of immunity to caffeine seem the rare consequence of deft symbiotic mergings— such as those of the Coffee Borer (Hypothenemus hampei), who conspire with gut microbes like Pseudomonas fulva (Ceja-Navarro et al. 2015). In this case, the bacteria consume the caffeine and allow the Coffee Borer to live its life burrowing into a bean containing, according to the Lawrence Berkeley National Laboratory (2015), a lethal dose equivalent to 500 shots of espresso. The Coffee Borer seems to be missing out. But do these other organisms really get high?
Biologist Jakob von Uexküll is well-known for launching a research programme aimed at gleaning insights into other species’ lived experiences (ex. Uexküll 2010). According to him, by carefully observing an organism’s behaviour, we can see what ‘shows up’ in its environment as relevant and what is ignored, and use these to make inferences into how the world appears to that being. His intention was to create a science interrogating the subjective experience of the biotic world. He was well aware humans would never really know what it is like to be a bee. After all, we cannot really know what it is like even to be our own spouse or child. But we can get ever closer, especially if we try. For example, many people are familiar with studies revealing that bees see a different spectrum of light, and hence floral patterns invisible to our eyes. This is an example of an insight falling within an Uexküllian focus.
Does caffeine tell us anything about the lived experience of other creatures? As far as I know, Uexküll never asked this question. Some would deny it, arguing that another species gets hyperactive and jittery when on caffeine does not indicate they consciously experience it. It merely shows that caffeine produces stereotypical physiological reactions. If a conscious organism ingests caffeine, then it obviously would experience those physiological reactions. However, the majority of the biotic world is not conscious. The reactions just happen with their consequent ecological effects. Such a perspective forms the basis of a dominant assumption in biology research and it suffuses biology education too: if a biological system can be understood mechanistically, there is no need to appeal to consciousness. It is at best pointless; at worst, it is dangerous and anthropomorphic.
But, of course, those very same chemical changes occur in human physiology too, and the behaviour of a human on caffeine can also be understood mechanistically without appealing to human consciousness. And yet, human consciousness clearly exists. A double standard seems baked into biology. I am keen to find a way out of this. Perhaps if we figure out what role consciousness plays for humans, we can infer whether it is also active in other species. This turns out to be a difficult job, and one I am hoping another cup from my French press will help facilitate.
I’ll continue on my loosely Uexküllian trajectory. As humans go about their lives, they are generally trying to do things. To accomplish those things, some things matter and others do not. Our bodies filter out what does not likely matter, presenting only what is deemed relevant. These relevant features can then be seen in relation to one another. For instance, I am aware of a small subset of things right now: that the coffee is starting to scatter my focus, and that this conflicts with my writing deadline. Because I am conscious of these two things, I am able to realize that I should slow down my drinking. Consciousness is like a map of important features in ongoing play, a global representation of relevant internal states vis a vis relevant external features. Given the complexity and contingency of dynamic environments, it is likely all organisms would be faced with a similar situation: a lot more things are going on than a creature can attend to, and there is a need to respond only to what is relevant, instead of getting buried in details. Consciousness is that porous map.
I do not see other species waffling about, as we might expect if a global map did not exist to simplify the relationship between the organism and its world. Instead, I see other species’ focus directed by what is relevant to them. If caffeine interrupts or enhances that focus, it makes sense that this would show up too, as it would be relevant for the creature that its capacities had changed. Different decisions might be needed.
The consciousness of other animals is increasingly acknowledged by scientists (see for example the Cambridge Declaration on Consciousness [Low et al. 2012]), and is even posited by plant scientists (ex. Trewavas 2015), but Uexküll’s vision remains totally eclipsed in biology education. The assumption that life is nothing but mechanism pervades even apparently ‘progressive’ school provision, such as Scotland’s Curriculum for Excellence’s steadfastly mechanistic biology learning outcomes. What is the reason for this, and what effect does it have on the way children see the world? Who benefits and who loses when education is the buzzkill at the party? Some historians claim caffeine accelerated the Enlightenment (Pollan 2020). Could investigating its role in the biosphere enlighten schools too?
References
Ceja-Navarro, J.; Vega, F.; Karaoz, U. et al. (2015) ‘Gut microbiota mediate caffeine detoxification in the primary insect pest of coffee,’ in Nature Communications 6, 7618 Evogeneao https://www.evogeneao.com/en/explore/tree-of-life-explorer#bees-and-humans
Huang, R. ; O’Donnell, A. ; Barboline, J. & Barkman, T. (2016) ‘Convergent evolution of caffeine in plants by co-option of exapted ancestral enzymes,’ in Proceedings of the National Academy of Sciences 113(38), pp. 10613-10618
Khursheed, T.; Ansari,M. & Shahab, D. (2009) ‘Studies on the effect of caffeine on growth and yield parameters in Helianthus annuus L. variety Modern T,’ in Biology and Medicine 1 (2), pp. 56-60
Lawrence Berkeley National Laboratory (2015) ‘Gut microbes enable coffee pest to withstand extremely toxic concentrations of caffeine,’ July 14, 2015. Retrieved on November 21, 2020 from https://phys.org/news/2015-07-gut-microbes-enable-coffee-pest.html
Low, P. et al. (2012) ‘The Cambridge Declaration on Consciousness’. Publicly proclaimed in Cambridge, UK, on July 7, 2012, at the Francis Crick Memorial Conference on Consciousness in Human and non-Human Animals.
Mustard, J. (2014) ‘The buzz on caffeine in invertebrates: effects on behavior and molecular mechanisms,’ in Cellular and Molecular Life Sciences 71(8), pp. 1375-82.
Nathanson, J. A. (1984) ‘Caffeine and related methylxanthines: possible naturally occurring pesticides’, in Science. 226(4671), 184–7
Pollan, M. (2020) Caffeine: How coffee and tea created the modern world. Audible Original.
Trewavas, A. (2015) Plant behaviour and intelligence. Oxford, UK: Oxford University Press.
von Uexküll, J. (2010) A Foray into the Worlds of Animals and Humans: With A Theory of Meaning. Minneapolis, MN: University of Minnesota Press.