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.