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In this post, I’ll argue:

1. Nonhuman animals possess moral value.
2. Their moral value is significant in contexts beyond human exploitation, including their suffering as prey in natural ecosystems.

The Argument from Species Overlap

Let’s begin with the foundational question: Do animals matter morally?

Opponents of animal moral value often argue that traits like advanced rationality, self-awareness, or moral agency are necessary for moral consideration. Since animals lack these, they fall outside our ethical circle.

But this logic fails when applied consistently. If animals did not have moral value simply because they lack one or more of these traits, then marginal cases of humans would also be excluded. We do not want to say that they also lack moral value simply because they are missing those traits. These humans include, for example, infants, the severely cognitively disabled, or individuals with advanced dementia. They lack the same traits used to exclude animals, yet we (rightly) deem it abhorrent to deny them moral value.

Consider:

• P1: If moral value depends on trait X (e.g., rationality), then any being lacking X lacks moral value.
• P2: Marginal humans lack X.
• C: Therefore, marginal humans lack moral value.

Yet almost no one accepts that conclusion. To resolve this, we have two options:

1. Bite the bullet: Deny moral value to marginal humans.
2. Expand the moral circle: Acknowledge that trait-based thresholds are flawed, and grant moral value to animals.

Since the first option is morally repugnant—and likely unthinkable to most readers—the second option seems to be the one we must choose.

To put the argument differently:

• P1: If an ethical stance grants moral value to humans who lack trait X (e.g., rationality), then it must grant moral value to animals who also lack X.
• P2: Humans such as infants or the severely disabled lack X but still retain moral value.
• C: Therefore, animals lacking X must also retain moral value.

To reject the conclusion, one must either:

1. Deny moral value to marginal humans (a repugnant option), or
2. Identify a morally relevant trait that marginal humans possess but animals lack.

No such trait survives scrutiny. Appeals to special traits, “humanity,” or even potential fail (for instance, developmental rationality expected in infants breaks down when applied to permanently disabled humans).

The default presumption is that when harm is inflicted, the burden of proof lies with the perpetrator, not the victim. To justify treating animals worse than humans, one must:

1. Identify a trait T that distinguishes the groups, and
2. Show why T is morally relevant to the specific harm being inflicted.

Suppose you want to kill pigs for food and justify this by claiming “pigs lack self-awareness!” Does lacking self-awareness justify slaughter? If so, then humans in persistent vegetative states (who also lack self-awareness) could equally be farmed. Absent a coherent T, the differential treatment appears arbitrary.

Having established that trait-based thresholds fail to exclude animals without also excluding marginal humans, critics might retreat to a simpler symmetry-breaker: “But humans are special because they’re human.” In other words, the morally relevant differences between humans and nonhuman animals that would justify treating them differently in terms of mass killing for consumption are not about ‘intelligence’ or ‘rationality’ but about their humanity. ‘Humanity’ is the trait that breaks the symmetry. After all, the senile, infants, the mentally disabled, and other marginal cases all share the trait of being human.

This objection typically manifests in two forms, one biological and the other tribal.

1. Species Membership: DNA

The Claim: “Humanity” is defined by membership in Homo sapiens—i.e., beings whose DNA traces back to Homo erectus. Thus, even marginal humans deserve moral consideration, while animals do not.

The Rebuttal: Genealogy is morally irrelevant. Consider a thought experiment where archaeologists discover Homo fictus, a species identical to humans in intelligence, sentience, and social bonds, but with DNA tracing to a different hominin lineage. Under the species-membership criterion, farming, experimenting on, or slaughtering Homo fictus would be morally permissible—a conclusion so repugnant it collapses the premise. If we wouldn’t exploit Homo fictus, we cannot justify exploiting pigs, cows, or chickens based solely on lineage. As A.W.F. Edwards noted, genetic differences among humans are non-trivial. If moral equality were based solely on biological similarity, any discovered dissimilarity (e.g., IQ variance, disease susceptibility) could justify hierarchy.

2. In-Group Membership: Tribal

The Claim: “Human” signifies in-group loyalty. We prioritize humans for the same reason families prioritize kin: moral value derives from affiliation rather than solely from objective traits.

The Rebuttal: This logic justifies any arbitrary in-group preference. For example, slaveholders claimed moral superiority over enslaved people based on race, and patriarchs denied women rights based on sex. In-group bias, when universalized, licenses oppression. This argument has been, and continues to be, a playbook for justifying eugenics and caste systems.

If neither traits, tribe, nor taxonomy can justify excluding animals, what remains? I argue that it is sentience (the capacity to have subjective experiences and feel pleasure and suffering). Every proposed “cutoff” for moral consideration—intelligence, language, moral agency—collapses under the weight of marginal human cases. Sentience is both necessary and sufficient for moral relevance. To experience suffering, pleasure, or desire is to have interests that can be harmed or fulfilled.

Does this mean that Non-Human Animals Have Equal Moral Value to Humans?

Moral value need not be binary or identically weighted to demand ethical action. A dog’s suffering need not “equal” a human’s to warrant concern. What matters is whether suffering exists and whether it can be mitigated without disproportionate cost. Even if humans were granted greater moral weight than non-human animals, inflicting vastly more suffering on animals (for instance, slaughtering 80 billion land animals annually) would still require a proportionally stronger justification. Does “taste pleasure” outweigh trillions of hours of suffering? The math rarely holds.

If sentience ‘grounds’ moral value, and no defensible symmetry-breaker exists, we face an obligation to reduce suffering systematically. But does this obligation extend beyond human exploitation, even when humans are not the cause?

Wild Animal Predation

The argument for animal moral value becomes thornier when applied to natural suffering. If we accept that sentience grounds moral concern, should we intervene to prevent predation, disease, or starvation in the wild? Consider the following scenarios:

Scenario A (Xenomorphs):

A xenomorph species evolved to prey on humans. You’re in a helicopter with a sniper rifle, poised to kill one before it hunts a human. Your immediate intuition might be: shoot first, ask questions later. Most would prioritize human life over xenomorph autonomy or ecological balance.

Scenario B (Lions):

A lion stalks a gazelle. You have the means to kill the lion and spare the gazelle, yet your intuition is: “Don’t shoot!”

Why do we treat these cases differently when both involve sentient beings harming others for survival? Some may cite an ‘ecological’ defense: predation is morally neutral because it is part of the natural order or ecosystem stability, and intervening would cause cascading harm (such as overpopulation or starvation).

The problem with this reasoning is that in Scenario A, few consider the xenomorph’s ecological role—while in Scenario B, ecological impact dominates. This represents an anthropocentric scope neglect, where consequences are weighed arbitrarily for nonhumans. Moreover, even if ecosystems were the consistent basis for evaluation, humans remain the species most responsible for environmental degradation. Prioritizing xenomorphs over humans would be, ecologically speaking, ideal only in theory.

As with factory farming, predation ethics demand a morally relevant trait distinguishing human and animal victims. Yet:

• Sentience: Both humans and gazelles experience terror and pain.
• Ecological Value: Humans cause net ecological harm, while gazelles may be neutral or beneficial.
• Agency: Predators (whether xenomorphs or lions) lack moral agency.

No trait justifies the asymmetry in concern without invoking circular logic.

Trophic Ethics: Odd-order Predator Culling

The concept of “odd-order killing” is a theoretical framework encountered in online discussions. It aims to minimize harm in ecosystems by targeting predators at specific trophic levels. The idea classifies predators by their position in a simplified linear food chain and targets those in odd-numbered positions to indirectly protect herbivores. Consider a linear, five-step food chain:

grass → grasshopper (herbivore) → frog → snake → eagle

Each level is numbered sequentially, with the herbivore at position (a). The predators are then labeled according to whom they prey upon:

Position

Organism

Role

Preys On

(a)

Grasshopper

Herbivore

Grass (producer)

1

Frog

1st-order carnivore

Grasshopper (a)

2

Snake

2nd-order carnivore

Frog (1)

3

Eagle

3rd-order carnivore

Snake (2)

Odd-order predators occupy positions 1, 3, 5… in the chain. In this example:

• Frog (1): Directly preys on the herbivore (grasshopper).
• Eagle (3): Preys on the snake (2), which in turn preys on the frog (1).

These odd-order predators are critical targets because their removal can theoretically reduce herbivore predation through two ways in this chain:

1. Direct Intervention (Kill Frog)

Eliminating the frog (1) removes the immediate predator of grasshoppers. Grasshoppers survive, but frogs no longer regulate their population.

2. Indirect Intervention (Kill Eagle)

Killing the eagle (3) stops it from preying on snakes (2). As the snake population increases, more snakes prey on frogs (1), leading to fewer frogs and ultimately fewer grasshoppers being eaten. In this way, grasshopper survival improves through a cascade of trophic effects.

On the other hand, the snake (2) is an even-order predator and should not be directly targeted. Removing it would allow frog (1) populations to grow unchecked, potentially leading to increased predation on grasshoppers.

The problem with this line of argument is that many predators fulfill multiple trophic roles. A snake (2) might prey on both frogs (1) and grasshoppers (a), and removing a predator could destabilize the ecosystem by triggering overpopulation or cascading effects. At any rate, while the pragmatic reality may justify differential treatment of humans and nonhumans when it comes to predation, it clearly does not do so in the context of humans actively breeding billions of animals into existence and slaughtering them en mass.