44 pages • 1 hour read
Zoë SchlangerThe Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth
Nonfiction | Book | Adult | Published in 2024A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.
Chapters 9-11Chapter Summaries & Analyses
Chapter 9 Summary: “The Social Life of Plants”
Certain insects are described as “eusocial,” meaning they participate in a form of collective behavior that emphasizes the benefit of the whole over the survival of the individual. Ants, bees, and humans all exhibit eusocial behavior. In Chapter 9, Schlanger asks whether plants also can engage in eusocial behavior. Some research suggests they do.
Evolutionary ecologist Susan Dudley discovered that searocket plants behave differently around their own kin than they do other plants. When planted close to unrelated plants, searockets take an aggressive approach, pushing out the roots of other plants, taking up space. When planted close to their relatives, however, searocket plants are more amenable, leaving enough space to share nutrients with their kin. Dudley shared with Schlanger that the only reason she made this discovery was because she consciously set aside the scientific assumption that plant behavior is driven by evolutionary benefit. Instead, she asked if something else might be happening.
There are numerous examples of plants changing their behavior to prioritize the well-being of plants with close genetic markers. Sunflower farmers in Argentina discovered that planting relatives close together could increase yields, as these plants shared space more effectively than when partnered with unrelated rivals.
How plants know whether they are close to a relative is still a mystery, but Schlanger points to earlier chapters, which detailed the complex ways plants communicate and interact with the world around them. Research by Dudley and others has raised questions about the traditional farming practice of prioritizing aggressive plants over docile ones. Farmers often select the most viable and vigorous plants, thereby inadvertently ensuring the offspring of a more aggressive and competitive plant over an altruistic one.
Furthermore, plants appear to be affected by their symbiotic relationships and environments in similar ways to humans. When a plant is stressed, for example, it makes poor “foraging” decisions in its roots, establishing them in places where there is little to no nutritional value. Similarly, when humans are stressed, their cognitive functioning is inhibited. Research indicating that plants engage with the world this way—including sacrificing one’s own growth for that of a relative—suggests that the traditional “survival of the fittest” model may not explain everything happening in the plant world.
Chapter 10 Summary: “Inheritance”
Schlanger extends her investigation into the social lives of plants by examining how they parent. In recent years, the scientific community has focused on the plant genetics and how those genes are passed from one generation to the next. High school biology students are taught Mendel genetics, a law of inheritance established by Gregor Mendel that studies patterns passed from parent to offspring, but this framework only accounts for a portion of a complex system of heritage.
Plants appear to exhibit maternal care. For example, the plant Spigelia genuflexa bends its stem, sacrificing itself to plant its seeds in soft moss on the forest floor, where its offspring has the greatest chance of surviving drought conditions. Plants can also speed up their genetic processes by ensuring their immediate offspring are more prepared to face challenges. Cool climates can cause a plant to increase the thickness of a fruit wall or coat of a seed. Schlanger argues that this reveals an important part of genetics that is often overlooked: the role of the environment. Life is impacted by a mixture of both experience and genetics.
Plant evolutionary ecologist Sonia Sultan has devoted her career to understanding how this ecological approach may shift how scientists think about plants. Sultan argues that an emphasis on genes has limited science’s understanding. She cites a simple study from 2000 on people with the lung cancer gene. This gene, passed down from parents, increases the risk of lung cancer from smoking. However, study subjects who ate cruciferous vegetables like broccoli could lower their risk of lung cancer despite having the gene. If they ate enough cruciferous vegetables, they could eradicate the impact of the gene altogether.
Sultan shares the study to show that genes and ecology are part of the same complex system. Schlanger asserts that this also calls into question the nature of individuality itself: “Perhaps our ‘essence’ was more flexible than we thought. Perhaps it was contiguous with, and not separate from, our environment” (230).
Chapter 11 Summary: “Plant Futures”
Schlanger visited Tony Trewavas, a lifelong researcher, at his home in Edinburgh. Trewavas focused on network theory, emphasizing the interconnected and highly complicated web of systems that comprise life and perhaps even intelligence. Trewavas explained that scientists too often hyperfocus and hyperspecialize on singular points rather than embracing a more collective understanding. He suggests this is because humans are wired for limited perception: “We find it not easy to feel the system in which we actually live” (243). When Schlanger asked Trewavas what he thought would happen if scientists took a systems approach to research, Trewavas said he was not sure.
Early in their conversation, Schlanger realized that while Trewavas held a glowing opinion of plants, he had a dim view of humanity. Trewavas suggested that humans had already surpassed their threshold for understanding the complexity of plants and making that knowledge useful. He was certain humans were past the point of their own destruction. Schlanger prickled at Trewavas’s attitude.
Unwilling to write off the fate of the planet, plants, and humans just yet, Schlanger proposes that a shift in thinking toward a more collectivist approach could change the course of the future. The question of plant intelligence is a social one, driven by how people think about themselves and their relationship with the external world. When humans embrace an Indigenous scientific approach, seeking answers to how all things intermingle and connect, then they begin to see the impact of their behaviors on the wider system.
Chapters 9-11 Analysis
In this final section, Schlanger merges her previous discussions about the differences between plants and humans or animals. She examines the social behavior of plants, the ways they pass on genetic and nongenetic information, and the implications of research into plant intelligence on the future. This is the culmination of Schlanger’s exploration of The Complexity of Ecology. Rather than shying away from correlating humans and plants, she embraces the comparison. Chapter 9 opens with a discussion of the eusocial behavior of insects, the prioritization of the good of the whole over the individual. Historical scientific understanding is centered on the idea that plants prioritize what is most advantageous for the individual—engaging in a continuous struggle to survive and compete. However, research indicates that some plants exhibit eusocial behavior, which conflicts with that traditional understanding of plant life.
Schlanger’s curiosity about the correlation between human and plant experiences contributes to her assertion that all life is the product of a complicated web of systems: “If I’ve learned anything, it’s that if something works well, biology tends to reproduce it across the spectrum of life. A good idea has a habit of showing up again and again” (194). The very title of Chapter 9—“The Social Life of Plants”—emphasizes this connection. Searocket aggressively seeks nutrients and takes up space unless it is surrounded by its own relatives. Then it behaves in a more polite manner, making room for its neighbors and sharing resources. Some flowering plants related to one another will expend more energy developing full and bright flowers than normal to draw more pollinators to their collective genetic offerings rather than reserving energy for their own seeds.
It is important to note that these examples of The Constant Motion of Biological Creativity have significant evolutionary advantages. The survival of a plant’s relatives ensures the distribution of its genetic line. However, sharing resources with kin also suggests that plants have a sense of self and otherness; in short, they can recognize family members. This recognition is also seen in the way plants pass information to their offspring. Schlanger explains that this process involves far more than Mendel’s genetics. In fact, genetics account for only a small percentage of what determines a plant’s traits. The environment plays a huge role, and so does the parent’s interference.
In previous chapters, Schlanger questioned the nature of Plant Consciousness through various lenses. These lenses mirror the philosophical discussions on the matter: consciousness as sensory experience, consciousness as decision-making and processing, consciousness as adaptation and creativity. Philosophers like Maurice Merleau-Ponty and John Locke emphasized the role of sensation and consciousness, while William James argued that consciousness is flowing and adaptive. These connections reveal the philosophy and science that Schlanger blends to support her claims. In this section, Schlanger poses consciousness as social behavior—the recognition of the self and the other, and the prioritization of the other over the self. She links this idea to Indigenous approaches to scientific inquiry and understanding.
These approaches uphold Schlanger’s argument about The Complexity of Ecology. Plants develop strong, complicated relationships among themselves and with other species. They communicate with insects and other plants. Plants and fungi have developed a highly complex relationship of mutualism. They may also communicate in many ways that scientists have not yet dreamed of, and this communication is critical to their evolutionary success. Schlanger suggests that by embracing ecological understanding and Indigenous approaches that blend spiritualism and science, humans stand a better chance of grappling with their own consciousness and position within a larger system:
‘Fittest’ here doesn’t mean what we thought it meant—it’s not about whoever manages to demolish their neighbors. This is more like survival for a while, until something changes. In a way, it’s an opportunity to shift our perspective while changes are causing a complex drama of decline and abundance at the level of individual plant species, in the end, the thing that survives is the biome, the whole community of life (213).
Framing plant research within a context of ecology provides a bookend to the Prologue, in which Schlanger highlighted her past as a climate reporter and her struggles to feel connected to the work. Each climate story felt like an isolated example of a larger problem—and the problem is that people fail to recognize how their lives contribute to complex systems. She emphasizes that in failing to give plants the credit they deserve, humans have overlooked the crux of plants’ evolutionary success: their ability to live within and prioritize the collective. This new way of thinking may provide both a path forward for humanity and a way to combat the climate crisis.
