“Intelligence is the ability to solve problems, and consciousness is the ability to feel things and have subjective experiences.”
~ Yuval Noah Harari
A prominent driver in the push for a plant-based or vegetarian diet is the ethical consideration regarding animal welfare. We strive to avoid practices that are stressful or painful for animals because we view them as intelligent, conscious, and sentient beings. Plants, generally speaking, and most members of Congress, not so much.
However, the current discussions regarding artificial intelligence have generated a resurgence of thoughts regarding intelligence, consciousness, and sentience. What do those mean, and how do we apply them – or do they apply at all – in discussions ranging from AI to other forms of non-animal life, like plants?
As Prof. Harari has observed, intelligence can be defined as the ability to solve problems. Consciousness describes the ability to feel things and have subjective experience, and sentience can be outlined as the “capacity of an individual, including humans and animals, to experience feelings and have cognitive abilities, such as awareness and emotional reactions. It encompasses the ability to evaluate actions, remember consequences, assess risks and benefits, and have a degree of awareness.[1]”
Recent advances have allowed us to push the boundaries of investigation in these areas, particularly with respect to the world of plants, which includes the fruits, vegetables, legumes, and grains that have been part of our and our forebears’ diets since the dawn of humankind. A recent review explores what might be considered nontraditional sentience within the plant kingdom and its implications.
- The review focused on the phenomenon of plant memory
- Like people, the genes of plants can respond to environmental conditions through epigenetic phenomena.
- Like people, those changes can be passed to future generations in a process known as transgenerational plasticity.
- Plants continuously receive and integrate environmental information and adjust their growth and development to favor fitness and survival.
- This integration of information affects subsequent life stages of the plant and/or the development of successive generations; it can be considered an ‘environmental memory.’
- This environmental memory can include both abiotic information (temperatures, water conditions, etc.) and biotic information (pests and diseases) across different time scales (e.g., diurnally or seasonally).
- Plants may be more likely to pass on epigenetic changes to offspring because compared to mammals, plant gametes (the reproductive cells used to produce a new organism) form post-embryonically, which increases the possibility of heritable adaptive DNA changes in response to the environment.
The Caveat:
Terrestrial plant life first emerged approximately 500 million years ago, or about 125 million years before the first land animals appeared. According to Professor Michio Kaku’s concept of civilizational advancement (Stages 1-5) based on the Kardashev Scale (developed by Soviet astrophysicist Nikolai Kardashev in 1964), that is a lot of time for the development of intelligence, consciousness, and sentience in forms that may not be immediately recognizable to us.
For example, Prof. Kaku currently estimates our modern global civilization to be 0.7 on this scale, projecting that we would require a century or several more to become a Type 1 civilization. A type I civilization is one that has achieved planetary unity with advanced technologies, global communication, and perhaps even a unified government. It is also capable of controlling natural phenomena (like weather) and might be well on its way to managing global crises (such as climate change and energy shortages).
He further estimates that it could be an additional several million years of evolution before we achieve a Type 3 civilization. This represents a galactic civilization with super-advanced technology, such as faster-than-light travel (if possible) or alternative methods of interstellar travel. Such a civilization would have achieved a deep understanding of currently undiscovered physics, allowing the harvesting of energy and information from such cosmic sources as black holes, dark matter, and other galactic phenomena. What could plants have achieved with a 125-million-year head start?
Here are a few of the areas of investigation expanding beyond just plant memory, because the broader research reveals plants’ abilities to not only process information and respond to their environment (as highlighted in the review above), but also communicate, albeit in ways very different from animals.
1. Plants Perceive and Respond to the Environment
- Sensory Perception: Plants can sense and respond to environmental factors like light, gravity, temperature, moisture, chemical, and other abiotic information. As discussed above, plants then process that information in complex ways either responding themselves (within generational epigenetic changes), passing the information and knowledge to future generations (transgenerational plasticity), or both. Plants even recognize mechanical signals like touch, which can affect growth patterns, such as in vines that “feel” their way to a support structure.
- Threat Responses: When attacked by herbivores, plants can produce chemical compounds like toxins or bitter substances to deter further grazing. They can also release volatile chemicals to attract predators of the herbivores that are harming them, effectively communicating to and recruiting allies in their defense. These warning signals can also be communicated to neighboring plants, e.g., via plant pheromones, allowing plants in a local environment to “talk” to each other. Plants can also pass on this information to future generations, such that plants subjected to an attack on their root system can pass along via genetic changes the information on how to combat that attack to their offspring (a generational form of long-term memory) if and when a similar challenge confronts them.
2. Memory and Learning
- Mimosa pudica: Experiments with the “sensitive plant,” Mimosa pudica, demonstrate how the plant folds its leaves when touched. Yet, its more than a singular response, the plant “learns” over time. After initially folding in response to liquid drops, researchers found that the plant stopped folding its leaves after realizing the drops weren’t harmful, and it retained this ‘memory, for days, indicating a type of learning behavior; albeit very different from animals (including humans) with a brain and central nervous system.
- Habituation: Plants can become habituated to stimuli over time. For example, plants exposed to regular, non-harmful mechanical stimulation (like shaking or wind) may show reduced responses over time. This habituation indicates that plants can “learn” to distinguish between harmless and harmful stimuli.
3. Communication and Social Behavior
- Root Communication: Roots release chemical signals to communicate with neighboring plants. Research shows that plants can recognize kin and alter their growth patterns to compete less aggressively with genetically similar plants nearby while competing more aggressively with non-kin. Plants can also communicate via their root system with other non-animal species like fungi and conduct ‘trade,’ whereby the plants exchange glucose for minerals or other fungal products.
4. Problem-solving and Adaptability
- Resource Allocation: Plants demonstrate flexibility in resource allocation. When resources are limited, they can adjust root growth to access nutrients or water in specific soil regions, an action that mirrors problem-solving.
- Circadian Rhythms and Predictive Behavior: Plants exhibit circadian rhythms that help them anticipate environmental changes. Some even adjust leaf movements in anticipation of sunrise and sunset, indicating a capacity to “predict” periodic changes.
5. Electrical and Chemical Signaling Networks
- Signaling Mechanisms: Plants have complex electrical and chemical signaling networks that function similarly to our nervous system. For instance, when a leaf is damaged, electrical signals travel through the plant to initiate defense mechanisms, showing a coordination process across tissues, much as we may activate our immune system after we suffer a cut.
Whether intelligence, consciousness, and sentience are limited to animals or even just humans is another philosophical discussion. However, as that one boundary expands and starts to blur as it has in discussions regarding artificial intelligence and artificial life (perhaps better labeled non-organic or non-carbon-based life), so we should look at the other goalpost with similar scrutiny. If these lifeforms can respond to their environment, adapt to threats, engage in predictive and rhythmic behavior, solve resource allocation problems, communicate to their own kind and even to other species, preferentially nurture their own offspring, and acquire information that allows them to positively respond to survival challenges, and pass that information to future generations, do they not have some form of awareness that demands respect? It may not be intentionality and consciousness in familiar human terms, but perhaps it is a unique kind of intelligence and consciousness that can help us expand ours.
[1] (Broom, 2019)
The Study:
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