Do Microbes Matter More Than Humans?

Microbes aren't as charismatic as megafauna, but they outnumber humans—and their welfare deserves consideration.

Growing up, most of the stories I heard about animals featured charismatic megafauna—“flagship species,” as they were called. Elephants and tigers were the main attraction in zoos; dolphin shows were the primary draw at aquariums; and nonprofit organizations like the World Wildlife Fund celebrated pandas. In the news, the biggest stories about animals featured species like gorillas, lions, and orcas. This is largely still true today, and in a way it makes sense. These animals, with their sheer size, enigmatic behavior, and endangered status, can captivate the human imagination and command attention like few other creatures can, eliciting deep emotional responses from people around the world.

Yet the past decade has seen increasing pushback against this idea of prioritizing the welfare of megafauna while ignoring less charismatic creatures. The view that we should extend our moral concern to more than just animals with faces is becoming more mainstream. But if we stop simply prioritizing the welfare of animals that are “majestic” or “cute,” how should we prioritize species? Should we be concerned about the welfare of fish, bivalves, or insects? What about microorganisms? If meat is murder, does that mean antibacterial soap is, too?

Most people can agree that all humans are part of the moral circle. That is, they fall within the imaginary boundary we draw around those we deem worthy of respect and consideration. Many vegetarians and vegans believe that animals—at least farmed land and aquatic animals—are too. But people often fail to consider the idea that insects, microbes, and even some future forms of artificial intelligence may deserve as much consideration as human beings because they might also have conscious experiences, like happiness and suffering. And if they can suffer, as Jeff Sebo, a philosophy professor at NYU, argues in a prescient new paper, we should probably try to prevent that pain.

Sebo considers these matters through the lens of utilitarianism—a moral theory that prioritizes doing “the greatest good for the greatest number”—and what philosopher Derek Parfit called the “repugnant conclusion.” Parfit argued that if we had to choose between (a) a small population where everyone has the potential for very high welfare and (b) a large population where everyone has a very low potential for welfare, we should consider choosing the one with the greatest total amount of welfare.

Counterintuitive or “repugnant” as it may seem, the better option may well be the larger population whose members have more happiness in total, even if they have less on average. Sebo follows Parfit’s reasoning to its logical conclusion: The planet’s incredibly large population of smaller life forms, like bugs, may actually have more welfare to consider than its much smaller human population.

Not long ago, the idea that any nonhuman animal deserved moral concern would have seemed very strange. The 13th-century theologian Thomas Aquinas believed that only humans matter because only they have “immortal souls” and the ability to reason. If it’s wrong to torture an animal, he thought, that’s only because it may cause harm to another human’s property. Enlightenment thinker René Descartes famously popularized the view that nonhuman animals are automata, capable of responding to stimuli but not of thought or feeling. This thinking only started to change in the West after generations of ethical philosophers began to parse the meaning of a now-famous quote by utilitarian philosopher Jeremy Bentham: “The question is not, Can they reason?, nor Can they talk? but, Can they suffer?”

It wasn’t until Peter Singer’s 1975 book, Animal Liberation, and Tom Regan’s 1983 book, The Case for Animal Rights, that the idea of extending moral consideration to nonhuman animals became popularized in Western analytic philosophy. These days, we also have scientific evidence that animals can experience happiness and suffering, so it’s harder to argue that there’s a fundamental difference between human and nonhuman minds.

We can’t be sure that bugs experience happiness or suffering (though there is increasing evidence to suggest some do). You may think the chances are pretty small. You likely think the chances are even smaller that organisms like microbes or artificial intelligence systems can have these or other feelings. But even if the chance that they are sentient is a tiny fraction of a percent, Sebo argues, these creatures exist in such tremendously high numbers—there are, for example, roughly 57 billion nematodes for every human on Earth—that their expected total welfare may still outweigh that of humans.

Of course, none of this means that we should abandon our human projects and spend our lives protecting microbes. (Though if you’d like to try, researcher Brian Tomasik has some interesting suggestions, like abandoning antibacterial deodorant and refraining from boiling vegetables.) For one thing, we don’t know how to measure or quantify subjective experience, and we can only guess at the likelihood that different creatures may be sentient. Crucially, not everyone agrees that “total” welfare is more important than “average” welfare. Finally, even if you do believe in this moral calculus, does this line of reasoning extend indefinitely? Does it include plants?

Some believe it does. Paco Calvo, a philosopher at the Minimal Intelligence Lab at the University of Murcia in Spain, argues in a new book (cowritten with Natalie Lawrence) that plants have both cognitive and emotional capacities. The authors suggest that plant behavior, like leaning toward the sun or unfolding leaves, may be more than automatic reactions. Plants can learn and make decisions, they argue, and their behavior appears goal-directed. I’m skeptical that plants have a conscious experience, and even more skeptical that they can experience positive or negative feelings. But maybe, Calvo and Lawrence suggest, we’re so “entrenched in the dogma of neuronal intelligence, brain-centric consciousness, that we find it difficult to imagine alternative kinds of internal experience.”

If there’s not enough at stake on Earth with respect to these complex moral considerations, consider that there are people who want to “help humanity flourish among the stars.” They hope to colonize the galaxies, ensuring that trillions of people have the opportunity to exist. Folks like Elon Musk are already eyeing nearby planets. But Musk’s dream is my worst nightmare. Life on Earth is difficult enough—if we can’t effectively reduce the suffering that happens on Earth, why multiply it across the universe?

Progress is possible, but at this stage we know almost nothing about what smaller creatures like microbes and plants may experience. For that matter, we have very little information about what it takes for any creature to be sentient. As we learn more, it would be irresponsible not to consider the experiences of nonhuman creatures in our moral calculus. After all, we often make incorrect assumptions about other species, so it wouldn’t hurt to have a dose of humility about our current understanding of the world.

For these reasons and more, Sebo is right to caution us not to make “high-stakes decisions through classical utilitarian reasoning alone.” The real world is, and always will be, much more layered and complex than any philosophical thought experiment, by design. The conclusion he comes to (which I share) is not that we should necessarily prioritize microbial welfare over human welfare, but that we should at least consider the well-being of microbes much more carefully than we currently do (which is to say, hardly at all). In other words, even if we “matter” more than they do, the moral significance of individuals who differ from ourselves may still be far greater than we currently appreciate. We have a long history of excluding certain sets of individuals from our moral circle, only to later regret it. To not learn our lesson this time, when trillions upon trillions may depend on it, would be truly repugnant.

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