Sentience is defined as the ability to perceive one's environment and translate those perceptions into various feelings, such as suffering or pleasure. This has little to do with a species' cognitive ability.

It's been argued that it is inappropriate to humanize animal behavior in this way. Yet, science can never be totally free from this anthropomorphism, and there's a solid argument as to why.

For one, humans can only ever think about animals by drawing on their own experiences, and this facilitates many of the research questions when studying other species. Yet, beyond scientific discovery, there is an ethical motivation for relating human emotions to animal experiences. Once we accept that other species might feel pain similar to what we feel, we become responsible for their suffering.

Anthropomorphism, when used responsibly, can add emotional meaning to the science of animal sentience.

But is there a distinction to be made between sentient species? After all, we are animals. Yet, humans differentiate ourselves from other types of animals. Our culture, and the taxonomies our fields of study rely on, demand categorizations of nature. But nature is not so obedient.

Research indicates that sentience extends to a wide range of animals. For example, chimps have been found to be generous, mice have exhibited empathy and honeybees have demonstrated pessimism. But because of the limits of human perception, we don't have sufficient ways to measure just how sentient non-human species are. It likely isn't a clear-cut answer of sentient or not sentient, but shades of grey.

Currently, most of the research on animal sentience has focused on vertebrate species and been mammal-centric. It is generally accepted that vertebrates (with the disputable exception of fish) are sentient, and that invertebrates are less-so. These evolving distinctions have made nonhuman personhood protections a messy legal area.

Admittedly, humans have something these other sentient beings apparently do not: The cognitive ability to create complex cultures which have allowed us to conceive of and communicate a claim of rights. But, as environmental researcher Uta Maria Juergens has argued, "If we pride ourselves on our unique intellect, we ought to also pride ourselves on assuming the responsibility that comes with it."

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