Peter Singer's seminal 1974 essay, "All Animals Are Equal," fundamentally challenged conventional human attitudes towards non-human animals. He argues that the common practice of affording vastly different moral consideration to beings based solely on their species is a form of prejudice he terms "speciesism." Singer's central thesis is that all sentient beings, regardless of species, deserve equal consideration of their interests. This principle, he contends, is a logical extension of the egalitarian principles that Western societies increasingly accept in their treatment of other humans. He identifies sentience—the capacity to feel pleasure and pain—as the crucial characteristic that grounds moral concern, asserting that any distinction made beyond this capacity is arbitrary and unjust.
Singer's argument begins by positing that the capacity for suffering is the vital characteristic that entitles a being to equal consideration. He draws a parallel between the discrimination faced by marginalized human groups, such as women and racial minorities, and the exploitation of animals. Just as proponents of sexism and racism once argued for inherent differences justifying unequal treatment, those who defend the current status of animals often rely on claims of human uniqueness, such as rationality or language. Singer dismantles these claims by pointing out their inconsistency: we do not deny moral standing to humans who lack these capacities, such as infants or those with severe cognitive disabilities. If we grant moral consideration to such humans, then consistency demands we extend it to non-human animals who also possess the capacity to suffer. He argues that intelligence or the ability to use language is not the basis for moral worth; rather, it is the ability to experience the world and its harms.
Furthermore, Singer critiques the utilitarian basis of many moral systems that, while aiming for the greatest good for the greatest number, often implicitly or explicitly exclude animals from the calculation. He explains that when we consider the "greatest happiness principle," we must include the happiness and suffering of all beings affected. The widespread practice of factory farming, for instance, inflicts immense suffering on billions of animals for the sake of marginal human convenience or pleasure, such as a preference for certain foods. This, Singer argues, represents a severe failure to consider the equal interests of these sentient beings. The economic benefits derived from such practices, or the cultural traditions that endorse them, cannot ethically outweigh the profound suffering experienced by the animals.
Singer’s call for "equal consideration of interests" does not necessarily mean "equal treatment." He clarifies that the specific interests of different beings may warrant different responses. For example, a pig’s interest in running freely in a field might be different from a human's interest in attending a university lecture. However, the weight given to these interests should be equal. The interest of a pig in avoiding pain is as morally significant as the interest of a human in avoiding pain. Therefore, practices that cause significant suffering to animals for trivial human gain are morally indefensible. This includes not only the conditions in factory farms but also animal experimentation that yields little or no benefit, and the entertainment industry's use of animals in cruel ways.
In conclusion, Peter Singer’s "All Animals Are Equal" presents a powerful ethical framework that advocates for the moral inclusion of non-human animals. By identifying sentience as the criterion for moral consideration and exposing speciesism as a prejudice akin to racism and sexism, Singer compels readers to re-evaluate their assumptions about human superiority. His emphasis on the equal consideration of interests, irrespective of species, challenges utilitarian calculations and traditional justifications for animal exploitation, laying the groundwork for a more compassionate and consistent ethical system.