• Jaishree Subrahmaniam

Why kindness matters: Lessons from the plant world

Upon being questioned what the first sign of civilization was, anthropologist Margaret Mead replied that it was a 15,000-year-old thighbone found at an archaeological site that had been broken and then healed. She explained that in the animal kingdom if you break your leg, you die. You can neither run from danger nor hunt for food. No animal survives a broken leg long enough for the bone to heal. A broken thighbone was indeed evidence that someone had taken the time to stay with the one who fell and tended the person through recovery. A healed femur indicated that someone had helped a fellow human, rather than abandoning them to save their own life. Helping someone else through difficulty is where civilization started. In this article, I will explore what kindness means, what are some of the evolutionary explanations behind it, and what I learned about kindness from my research on plants.

Niceness is when we try to climb the social ladder, but kindness is how we lift others up

The difference between being nice and being kind can be understood if one tries to understand the intentions behind doing an action.

Fig. 1. Difference between being nice and kind. (Source: ithrivegames.org)

The nice person is externally motivated. Driven by the need for approval and validation from other people, this person craves acceptance and is fearful of rejection. On the other hand, a kind person is internally motivated. The compassion he/she has for others comes from his/her positive self-regard and not from the need to please.

The easiest way to distinguish between being nice and kind is to identify if there are underlying expectations behind an act. If you wave “good morning” to someone walking by, do you get mad when they do not wave back? Or, if you hold the door open for someone, do you get upset when they do not say, “thanks” as they pass? If you get offended when people do not offer you praise for being “nice” then you can be certain you are not being kind.

Being kind to someone means that the only thing on your mind is another person’s well-being when you act. Kind or altruistic acts mean that you do something for the benefit of another, without needing a return or payback.

Altruism: A stubborn anomaly of nature

In evolutionary biology, an organism is said to behave altruistically when its behavior benefits other organisms, at a cost to itself. The costs and benefits are measured in terms of reproductive fitness, or the expected number of offspring. So, by behaving altruistically, an organism reduces the number of offspring it is likely to produce itself but boosts the number that other organisms are likely to produce. Darwin himself was puzzled by this phenomenon, as it was a fatal challenge to his theory of natural selection.

If all life is a "struggle for survival of the fittest", why would any organism help another? He gave the answer himself in his book “The Descent of Man”- “When two tribes of primeval man, living in the same country, came into competition, if (other circumstances being equal) the one tribe included a great number of courageous, sympathetic and faithful members, who were always ready to warn each other of danger, to aid and defend each other, this tribe would succeed better and conquer the other. […] A tribe rich in the above qualities would spread and be victorious over other tribes: but in turn, overcome by some other tribe still more highly endowed" (Darwin 1879, p. 155)

Altruism benefits the entire group. Altruistic behavior is common throughout the animal kingdom, particularly in species with complex social structures. In numerous bird species, a breeding pair receives help in raising its young from other ‘helper’ birds, who protect the nest from predators and help to feed the fledglings. Vampire bats regularly regurgitate blood and donate it to other members of their group who have failed to feed that night. In social insect colonies (ants, wasps, bees, and termites), sterile workers devote their whole lives to caring for the queen, constructing and protecting the nest, foraging for food, and tending the larvae. Such behavior is maximally altruistic: sterile workers obviously do not leave any offspring of their own and have personal fitness of zero, but their actions greatly assist the reproductive efforts of the queen. My Ph.D. research focused on identifying if plants are capable of such complex behavior as well. Spoiler alert, they do!

Could plants cooperate with each other? Insights into my Ph.D. research

In nature, plants are seldom found alone. Be it meadows, backyard gardens, or forests, plants can be easily seen in large numbers of same as well as different species. Interactions between two individual plants could range from the competition (- -) to reciprocal helping (++) through commensalism (+0) and asymmetrical relationships (+-) (Subrahmaniam et al. 2018). Scientists have spent decades trying to understand the complexities of these interactions and their ecological consequences, yet there is a lot we still do not completely understand social relationships in a natural plant community. My Ph.D. research was focused on one of the most interesting interactions that occur between two plants: reciprocal altruistic/cooperative interactions (Trivers 1871).

Imagine your backyard, or a garden, or any other place where wild plants grow. Chances are, you see more than one individual of a particular plant species. A genotype is defined as the genetic constitution (genome) of a cell, an individual, or an organism, and multiple genotypes (of the same as well as different species) can make up a plant population. And populations of different species make up plant communities. Studying how the genotypes of a single species interact with one another are postulated to be key to understanding how plant populations evolve (Ehlers et al. 2016). There is just one problem though- this requires huge collections of natural plant genotypes that occur together in nature. Also, to understand these ecological interactions implies conducting huge experiments dissecting pairwise interactions between each combination of the collection of genotypes. Such a feat has not been fully embraced by ecologists yet, and my Ph.D. was a starting point which will hopefully pave the way for many such experiments in the future.

Understanding positive interactions in plants involved a plethora of trials and failed experiments, as well as literature review from across multiple disciplines (from ecology, evolution to mathematics, and sociology). But more importantly, it required a stubborn belief that if nature shaped other organisms to have the ability to help one another, why not plants?

Skipping over all those overwhelming details, let me fast forward to tell you what the results from my three years of research yielded and why that is important not only for plant biology but the way we view relationships.

Theory suggests, that cooperative links should exist among individuals from the same population, as they have a shared coevolutionary history of experiencing their natural environment (Nowak 2006), and are supposed to be prevalent under stressful conditions (Bertness and Callaway 1994). In simpler terms, organisms growing together can understand when their neighbor undergoes stress and provide help whenever required. The more stress, the more help they exchange.

In my Ph.D., I studied the natural variation of genotypic interactions using natural populations of Arabidopsis thaliana, a model plant in plant biology. I identified two different strategies of positive interactions within natural plant populations, i.e., kin cooperation (KC) and overyielding (OY) (Subrahmaniam 2020). What this basically means is, when undergoing stress, there were some plant populations wherein all members helped their kin (genetically similar individuals) and other populations where members were found to help a stranger (genetically dissimilar individuals) of the same population. Importantly, the genomic regions underlying this variation of positive interactions also carried signatures of local adaptation, suggesting the underlying importance of positive interactions in shaping the evolution of natural plant populations.

How could positive interactions evolve in a population?

Ever since Darwin created his theory of evolution by natural selection, scientists and philosophers of science have been intensely debating how altruism could have evolved, and at what level does natural selection act-Individuals or groups?

Two distinct schools of thought exist to explain altruistic behavior in a group of organisms, both heavily supported by multiple eminent scientists. The traditional ‘individualist’ view holds that Darwinian selection usually occurs at the individual level, favoring some individual organisms over others, and leading to the evolution of traits that benefit individuals themselves. On the other hand, ‘group selection’ refers to the idea that natural selection sometimes acts on whole groups of organisms, favoring some groups over others, leading to the evolution of traits that are advantageous for the whole group.

To reconcile these two contrasting theories and to understand altruism between individuals across groups, an interesting theory has been put forth- the multilevel selection theory. The principle behind the multilevel selection posits that selection can occur on multiple levels of biological organization, including cells and/or groups. This view suggests that even if behaviors that benefit other individuals are selectively disadvantageous at the level of the individual, they might still evolve if they are advantageous at—and hence selected for on—a higher level of the biological hierarchy (e.g. on the group or colony level). Altruism, for instance, is costly for the altruistic individual, but groups containing a higher proportion of altruistic individuals usually have a competitive advantage over groups that are composed mostly of selfish individuals (Kramer and Meunier 2016).

In simpler terms, altruistic behaviors could evolve within individuals if there is a factor (or stress/selection pressure) that acts on just specific individuals and requires cooperative effort to overcome. But it also means, that if there are external selection pressures acting upon whole groups, cooperative behavior for helping each other within those groups could also evolve. And that would also be natural selection!

Fig. 2. A simplified graphical model of multilevel selection. In social dilemmas, outcomes depend on the level of organization on which selection operates most strongly. To determine the dominant level of selection, the direction and magnitude of selection at the relevant levels should be estimated and compared (Source: Waring et al. 2015)

Darwinism revisited: Survival of the kindest

Being a plant biologist, I have always been in love with understanding the complex behaviors of plants. My Ph.D. was about understanding whether the ability to help one another exists in plants.

Three years of my research gave the first-ever evidence that plants can understand if their family member is undergoing stress, empathize, and extend support as and when required. What is better is that this ability is encoded in their genetic code. I think somewhere along with my Ph.D., I realized that what my plants told me could be applied to us (humans) on many different levels; what it means to be an altruist, someone who thinks beyond themselves and about the greater good.

We all know that the theory of evolution is interpreted in terms of survival of the fittest, but Charles Darwin himself proposed that natural selection would favor the occurrence of compassion. In other words, he made a pretty strong case for the survival of the kindest! He wrote, "In however complex a manner this feeling may have originated, as it is one of high importance to all those animals which aid and defend one another, it will have been increased through natural selection; for those communities, which included the greatest number of the most sympathetic members, would flourish best, and rear the greatest number of offsprings".

From simple organisms like fungi and bacteria to ants, mammals, and even plants; all organisms in nature are equipped with the ability to help one another. This makes me question- “where did our species go wrong?”. Our nomadic ancestors used to cooperate with their groups. They collectively worked for searching for food and water and fighting off external threats to their groups. But the 7 billion humans alive today have a very different lifestyle. Altruistic and cooperative behavior, if and when it does occur is more often than not, restricted among friends or family. However, soldiers, doctors, teachers, etc. are some examples of humans being altruistic towards strangers. The healthcare professionals working tirelessly in the face of the COVID pandemic is an excellent example of the kind of altruism we are capable of.

Think about the world we are living in today. Our species is facing a multitude of external stresses today, from decline and deterioration of natural resources, loss of biodiversity, climate change, to the most recent pandemic. These are just a few examples that potentially threaten to wipe us out. Multilevel selection theory posits that upon facing external threats, groups could spontaneously start cooperating and helping one another out. Having spent three years on this subject, I often find myself musing what we could achieve if all of us come together, overcoming the barriers of race, religion, and countries to cooperate with one another to fight off these and many more threats that we collectively face as a species.

If nature designed all organisms to be of help to one another, maybe the biggest benefit that comes from our evolution may also be to help each other and to be kind to each other. And just maybe, being an empath may ultimately be the key to our survival.

Fig. 3. Ubiquitous nature of cooperation across organisms


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Ehlers, B. K., David, P., Damgaard, C. F., & Lenormand, T. (2016). Competitor relatedness, indirect soil effects and plant coexistence. Journal of Ecology, 104(4), 1126–1135. https://doi.org/10.1111/1365-2745.12568

Kramer, J., & Meunier, J. (2016). Kin and multilevel selection in social evolution: A never-ending controversy? F1000Research, 5(0). https://doi.org/10.12688/F1000 RESEARCH.8018.1

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Subrahmaniam, H. J., Libourel, C., Journet, E. P., Morel, J. B., Muños, S., Niebel, A., Raffael, S., & Roux, F. (2018). The genetics underlying natural variation of plant–plant interactions, a beloved but forgotten member of the family of biotic interactions. Plant Journal, 93(4), 747– 770. https://doi.org/10.1111/tpj.13799

Subrahmaniam, H. J. (2020). The genetics of intraspecific plant-plant cooperation in Arabidopsis thaliana. https://hal.archives-ouvertes.fr/tel-02531785/document

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