Are humans really blind to plants?
Societal Impact Statement
People tend to see plants as the background to life on Earth, but they are essential to our very existence in many ways. In 1999 two botanist-educators from the United States coined the term “plant blindness” to describe this condition, and to draw attention to the decreasing focus on plants in education. Here I argue that disregard for any organism that is not a vertebrate (like us) is the more pervasive problem, but that combatting plant blindness is a good place to start to improve education, awareness, and care for the other organisms with which we share planet Earth.
Summary
The concept of “plant blindness” was coined in 1999 to highlight the phenomenon seen in American (United States) education in which animals are perceived as more important than plants. Symptoms were lack of recognition of plants as important components of ecosystems, lack of understanding of how plants affect our everyday lives, anthropocentric ratings of animals as more worthy of care than plants, and inability to “see” that plants are more than background. I argue here that the deeper problem is not with animals versus plants, but with “animals with eyes like ours and backbones” versus everything else. Cockroaches, worms, and spiders are animals too, and without them the planet would be as barren as if there were no plants. So combatting the more pervasive issue needs to be at the background of our thinking as we move forward in combatting plant blindness. I here review the symptoms of plant blindness and relate this to ways in which we might begin to think about using recognition of plant blindness as a way to increase awareness and care for all of life on Earth.
1 WHO COULD BE BLIND TO PLANTS?
As I write this article in the beautiful garden created by Rachel Lambert Mellon at her home in Oak Springs in northern Virginia, it is hard to believe that such a thing as “plant blindness” could possibly exist. Here plants jostle against one another in a riot of textures and colors, they spring up from cracks in the pavement and they create a dynamic and vibrant landscape (Figure 1). Who could be blind to this? But maybe because I am a botanist (and #iamabotanist for sure!) I have cured myself of this affliction, and see plants in a different way. I am infamous amongst my colleagues for pictures I insist have a bird in them, but really have a tree or shrub centre-stage.
The botanists and biology educators Wandersee and Schussler (1999) coined the term “plant blindness” to highlight a phenomenon they saw as pervading American education—the preference for animals over plants amongst biology students. They built their theory on a body of work from psychology that showed human preference for images of vertebrate animals with forward-facing eyes over flowering plants. Subsequent work on the topic has tended to stick to this simplistic division of “plants versus animals”, with only lip service to what “animals” might be. I would argue that rather than “plant blind”, humans are in fact “everything-but-vertebrates blind”, a very different proposition given that 99% of Earth's terrestrial animal diversity is invertebrate (Larsen, Miller, Rhodes, & Weins, 2017; Wilson, 1992), and some families of beetles have more species than all of vertebrate diversity combined. So humans seem to be blind to the vast majority of organisms, not just plants. Both television programming and school curricula vastly over-emphasize vertebrates, although some strides have been made for the inclusion of insects—by far the most diverse group of animals on the planet! Plants though are a very good place to start, but we must keep in mind that they are a beginning, not an end in themselves.
The original definition of plant blindness had four elements (Wandersee & Schussler, 1999), let's call them symptoms: (a) an inability to notice or see plants in the environment; (b) failure to recognize the importance of plants in the biosphere and in human affairs; (c) failure to see, notice, or pay attention to plants in one's own daily life; and (d) an anthropocentric ranking of plants as inferior to animals.
2 SEEING BEYOND A WALL OF GREEN
These symptoms had been blamed—just as we blame a cold on a rhinovirus, or scarlet fever on a bacterium—on zoocentric teaching, on a sort of zoochauvinism in education, thus training generations to ignore plants. The advance that Wandersee and Schussler (1999, 2001) made was to look deeper and see that plant blindness was in fact something innate in human beings themselves; our own brains were part of the problem. Our inability to “see” plants relates to a visibility bias, feeding the “what you see is all there is” (WYSIATI) decision-making process undertaken by what Kahneman (2011) refers to as our “System 1”. When flowering plants are not flowering, their visual homogeneity and lack of edges means the human eye and brain in a hurry sees them as all the same—a wall of green. Because we are usually in a hurry, our “System 1” makes those snap decisions to ignore or pass by and then we move on. Empirical research on visual memory has corroborated the differences in human perception for plants and vertebrates (Balas & Momsen, 2014), with participants presented images in rapid sequence less able to recall having seen a plant.
So perhaps an inability to notice plants in the environment can be overcome by employing our “System 2” (sensu Kahneman, 2011) and stepping back and taking time to really look carefully, challenging our snap decision that this is all the same. Wandersee and Schussler (2001) also point out that students (at least in the USA, and in my personal experience in the UK) are taught less about plants than about animals (read vertebrates), so this too feeds the retrieval of information bias that relegates plants to the background.
But plants are not the background. In terms of species diversity, flowering plants are dwarfed by insects, but looking at another dimension the picture changes dramatically. Bar-On et al. (2018) estimated the biomass of different groups of organisms, in both terrestrial and marine habitats. Plants dwarf the rest of life on the terrestrial surface of the Earth. On land plant biomass is estimated to be 450 Gigatons, while all animals account for only 2 Gigatons, and of that arthropods amount to half (1 Gigaton). Humans and their livestock account for more than all mammals and birds put together by a factor of 10 (Bar-On et al. 2018). So which is more important, species-level diversity or biomass? In a way, this is like asking which of your children do you love more, both are important for the maintenance of functioning ecosystems. But the biomass data allow us to see that plants are organisms that occupy space in a particular way, whether a redwood or a duckweed, and thus generate a new way of seeing them as components of the physical biosphere.
No one should ever forget for a moment that all life depends on plants – without photosynthesis there would be no oxygen for we humans to breathe. Photosynthesis has also driven great changes in Earth's atmosphere over geological time, leading to formation and change in the physical surface of the planet (Beerling, 2017). Deep time is a difficult concept, humans typically think of the past in a very short-term way—natural habitats are those their grandparents experienced. So this short-termism compounds plant blindness by narrowing the narrative of deep time to a few charismatic creatures like dinosaurs. Bringing plants into the narrative alongside vertebrates as active players, rather than just as food, will be important for the understanding both of plants and of the enormity of Earth's history.
What about our inability to see plants as relevant to our daily lives? I once asked a group of schoolchildren from inner city London if anyone had eaten a plant today—I was met with a chorus of “No”—but when asked if they had toast or cereal—nods all around. More than half of the human population today lives in cities, and by 2050 that number is predicted to rise to 75%. This means most of us no longer grow our own food or participate in its harvesting and production. Even the cultural differences in the foods we eat are disappearing fast (Khoury et al., 2014); today our diets are more diverse, but more similar—we are all eating the same things, but lots of them. Many programmes worldwide attempt to overcome this by involving children in growing plants that provide food—school gardens, window boxes—all these can involve small humans in touching and interacting with plants that they then use in a very direct way. But there is a risk that these efforts will be swamped by the scale of industrialized agriculture—what if we begin to think of the plants we grow ourselves as different to those cultivated on a grand scale? Would that make a difference? I think it would, starting small and personal is good, but we need to think global as well.
Gardening and horticulture is another way in which plants are important in people's daily lives. The fact that television programmes about the Royal Horticultural Society's flower shows at Chelsea and Hampton Court are screened at prime time on the BBC, and that “Gardener's World” is a standard year-round television feature surely speaks to plants being visible and interesting to a segment of the population, at least in the United Kingdom. In many cultures plants are important spiritual parts of people's lives (e.g., Hall, 2011), as well as being useful day-to-day. So perhaps the challenge in overcoming plant blindness is more acute in urbanized societies where connections with nature in general are left behind; are developed-world botanists in danger of assuming everyone is just like them? Usefulness is often a criterion for inducing care and attention—you want to save something because it will come in handy one day. But focusing our attention on plants that are useful to us today lures us into a utility trap; and is unlikely to overcome plant blindness on its own.
3 PLANTS GROW, LIVE, AND FEEL
In his first edition of Systema Naturae, Linnaeus (1735) said “Lapides crescunt. Vegetablia crescunt & vivunt. Animalia crescunt, vivunt & sentiunt. Hinc limites inter haecce Regnae constitunta sunt” (Minerals grow. Plants grow and live. Animals grow, live, and feel. These are the limits of the realms of nature). This simple hierarchy of complexity sets up a scale of nature, a linear sequence of complexity if not of importance. Aristotle's concept of the “Scala Naturae” further developed to become an image of a ladder with humans (naturally) at the top during the Middle Ages, is conceptually compelling but fundamentally incorrect. All life on Earth shares DNA, so we are all related in a most fundamental way. The single picture in Darwin's On the Origin of Species (1859) illustrates this with a branching diagram (Figure 2), but still we humans like to see things as a linear sequence. In discussions of phylogenetic trees even the most phylogenetically literate can be heard saying “at the base of the tree”. In reality we are looking at a slice through a bush, all of the organisms that are alive today have made it—they are all equally “advanced” no matter whether they are a single-celled alga or a giraffe.
But what about animals feeling and plants “only” living? Wandersee and Schussler (1999) suggest that because plants are immobile autotrophs they are not registered as different; they only become visible when they engage in activity like flowering that induces pollination or fruiting that induces dispersal. But plants do behave, they just do it on a different time scale to humans, making it difficult for us to perceive without a great deal of patience. In the 1990s BBC television series “The Private Life of Plants” (Attenborough, 1995), the iconic British broadcaster David Attenborough showed plants in a compelling way—anyone who has seen that series will never forget the Rubus plant in fast-forward motion snaking through the forest undergrowth! Towards the end of his life Charles Darwin also studied plant movement (Darwin, 1880), and felt his book had indeed shown that all plants had the power of movement; the fact that he was bedridden meant he actually had the time and patience to observe it. Maybe we humans are in too much of a hurry.
The advent of new tools for looking at nature means that we now know feeling and sensing are not confined to animals. Understanding of the chemistry involved in plant signaling (e.g., Kessler, Diezel, & Baldwin, 2010; Skibbe, Qu, Galis, & Baldwin, 2008), including the production of chemical alarm calls to other plants (Kessler & Baldwin, 2002) means we can now see that plants also sense and manipulate their environment in very sophisticated ways. Trees “talk” to one another using chemical signals transmitted through mycorrhizal networks (Gorzelak, Asay, Pickles, & Simard, 2015). Defence signals transmitted through these mycorrhizal networks cause sudden change in neighburs, even those of a different species (Song, Simard, Carroll, Mohn, & Zeng, 2015); if that is not behavior, I am not sure what is!
So Linnaeus (1735) was wrong—plants too grow, live, and feel (e.g., Trewavas, 2015). After all, pain is just a chemical signal in vertebrates (including humans) as well. It has been suggested that human preference for animals (read vertebrates) over plants is due to our ability to feel empathy with them, and that one way to increase interest in and caring about plants is to anthropomorphise them (Balding & Williams, 2016). Conservation of plant diversity could be augmented by creating empathy, people are more likely conserve something they think is attractive or with which they identify (Berenguer, 2007). Research showing plants as sentient beings like ourselves means this is increasingly possible. But it can carry a cost, in that anthropomorphizing a single species or individual to create empathy with it means others are seen as being of lesser value (Root-Bernstein, Douglas, Smith, & Verissimo, 2016) and therefore disposable. Ultimately our goal needs to be the conservation of systems (Knapp, 2003), but it's hard to empathize with a system. It's a bit like the difficulty humans have in caring for an individual in distress versus a whole population.
So what do we do about combating the symptoms of plant blindness? I would argue that we now have the research and tools to bring modern science, not just our feelings, to bear on the four symptoms identified two decades ago (Wandersee & Schussler, 1999). Much of this information is not new; biologists have known that plants are important for a very long time indeed. But the ability to tell the stories of the centrality of plants to the planet is greater now than ever before—plants have been shown to do things, to behave, communicate, and react in fascinating ways. Sure, they are important as the structural components of communities, but they do so much more. It is a fascinating experiment to ask people to imagine a world without plants—they cannot. We would regret a world without tigers or pandas, but a world without plants is unimaginable.
In addition, there is increasing evidence that nature is good for human well-being—maybe it is time to play the selfish card. Dallimer et al. (2012) have shown that contact with diversity increases feelings of well-being, and Shanahan, Fuller, Bush, Lin, and Gaston (2015) have developed a dose–response model for well-being and exposure to green spaces. What these studies have in common is green spaces—it is exposure to plants that gives us benefit. Understanding the green background will do us good in a very concrete way. This is not to say that plants are the ONLY part of nature that brings health benefits to people, but it is clear that green, structurally diverse spaces are important for human health, especially as we become a more urbanized species. Plants, and flowering plants in particular, provide that green structural complexity we as a species need.
4 OVERCOMING PLANT BLINDNESS—A GOOD PLACE TO START
An important part of curing the symptoms of plant blindness, and blindness to the rest of nonvertebrate life on Earth, will be for humans to begin to see ourselves as part of the system, not outside of it with dominion over it. Homo sapiens is one species among many, and in a pretty species-poor group at that. That we depend upon others is an essential concept for engagement with the science of diversity going forward, and in a way, plants provide us with ideal ways to show our own need for the rest of life on Earth in concrete and engaging ways.
Plants ARE the planet, a large part of both terrestrial and marine ecosystems. So to keep our Earth—this “blue and green marble”—dynamic and functioning, overcoming plant blindness is a very good place to start.
ACKNOWLEDGEMENTS
I thank Dawn Sanders for inviting me to write this opinion piece and the staff of PPP, especially Bennett Young for shepherding it through the submission process while I was travelling; I thank the International Union of the Conservation of Nature (IUCN), The Rainforest Trust and the Global Crop Diversity Foundation for funding my travel and stay at the Oak Spring Garden Foundation as part of a workshop on Red Listing crop wild relatives; and Max Smith for providing the beautiful image of the gardens at the Oak Spring house; most specially, though, I would like to thank Peter Crane, whose generous offer of a few extra days at Oak Spring Garden gave me the time, space, and inspiration to think about plant blindness and to write this short piece.
