What Is Sentience and Where Is It Found?

As countries around the world attempt to define animal sentience and draft laws based on their definitions, understanding the thoughts and feelings of all animals is more important than ever.

What does "sentient" mean?

Simply put, sentient means the ability to have feelings. It’s the capacity for a creature to experience sensations and emotions.

It’s pretty easy to see that we humans are sentient. Imagine you wake up in the middle of the night, walk to your bathroom in the dark, but then you think you hear a noise downstairs, so you turn to run back to bed and accidentally stub your toe. In just a short timeframe, you’ve gone through the sensations and emotions of feeling groggy, frightened and then in pain—you’ll probably feel a bit grumpy the next morning, too.

Sentience is at the heart of how we perceive and interact with the world around us. It means that we have a point of view.

As it turns out, we humans have historically had an easier time recognizing our own sentience than we’ve had seeing it in the animals we share the planet with.

There was a time when philosophers and scientists believed that only humans were sentient and that all other animals were unfeeling, unthinking robots. Even René Descartes (the philosopher who coined the famous phrase, “I think, therefore I am,”) thought animals were basically automated machines, no more intricate than a cuckoo clock.

Fortunately, we’ve come a long way since then. Psychologists and other scientists have spent decades researching how other animals experience the world around them, and what kind of emotions they feel when exposed to positive and negative stimuli.

What makes a being sentient?

There are many ways to understand what makes a being sentient. Some of them very complex. Some of them more simple.

When determining whether an animal is sentient, scientists will often ask a basic but important question: “Is there something that it’s like, to be that animal?”

In other words, does a being have the capacity to have varied experiences, both good and bad? Can they feel contrasting emotions? Pain and pleasure? Anxiety and relief? Boredom and enjoyment? Hunger and thirst? Fear and excitement? The list goes on, encompassing many of the same emotions that we humans experience.

Some scientists and proponents of animal ethics say it all comes down to the very simple question, “Can this being suffer?”

The ability to suffer is an important ethical distinction, because it implies that not only does a creature have the ability to feel pain—the sensation of injury where they were hurt—but also an accompanying, negative emotion.

Are animals sentient?

There is a great deal of sentience across the animal kingdom. Mammals and other vertebrates usually get the most credit for being both intelligent and sentient. For example, anyone who has been lucky enough to live with a lovable canine would probably argue that their pooch has a distinct personality and expresses clear emotions. There’s scientific research to back up these claims, too. Dogs express an array of emotions ranging from excitement, contentment, joy and love to distress, disgust, suspicion and anger. A typical puppy will develop emotionally to about the equivalent of a two-and-a-half year old person.

But what about non-mammals whose sentience is harder to observe? Here are some creatures that are trickier for scientists to figure out, and what the latest research suggests.

Birds

Birds’ brains don’t have a cerebral cortex—the portion most heavily associated with consciousness. And yet, a recent study led by Professor Andreas Nieder, the chair of Animal Psychology at the University of Tübingen, trained crows to respond to a visual stimulus on a screen. The study found that when presented with harder-to-perceive signals, different crows responded differently to the stimuli.

This wasn’t just a case of some birds having better eyesight than others. Instead, it suggests “higher processing levels of the brain” that allow members of the same species to have unique experiences. Even more importantly, sometimes the crows seemed to respond to something on the screen, even when nothing was getting projected, suggesting that their “eyes were playing tricks on them,” meaning these birds have some sense of “subjective reality.”

Fish

Because fish look, act, and live in such stark contrast to us land-dwelling humans, it’s long been assumed that they are not able to think or feel emotions the way we do. That misconception has been losing more and more credibility in the scientific community in recent years, however. Most of the research on fish sentience has sought to determine whether they can feel pain or not. The answer: Yes, they can. In experiments, scientists have observed that fish avoid potentially painful situations, sacrifice a potential reward to avoid an accompanying painful outcome, and seek relief after undergoing a painful procedure. There is less, but equally promising, research on fish’s ability for feeling joy and optimism, as well. There’s much more for us to learn about the internal lives of fish, but it’s clear that they deserve to be treated humanely, just like any other animal.

Insects

The psychology of insects is a rather underdeveloped area in animal science. Globally, there has been an increasing trend in the farming of insects as a source of food. This has some researchers concerned about the lack of attention that’s gone into ensuring the insects involved in this industry are being treated humanely. A recent research article published in Applied Animal Behaviour Science explores the ability of crickets to experience stress; cases in which locusts learned information through association; the memorization capabilities of beetles; and the complex, emotional cognitive capacities found in bees. The authors conclude: “Our findings certainly support the notion that far more needs to be done to explore the cognitive capacities and emotional lives of insects.”

Crustaceans

In recent years, the question of whether or not crustaceans like lobsters and crabs are capable of suffering has been a hot-button topic in the scientific community. When used as a source of food, these arthropods are commonly slaughtered by being boiled alive—a horrifically inhumane method for a creature capable of feeling pain. In 2021, researchers for the London School of Economics and Political Science (LSE) reviewed years of data and studies in an attempt to clear up the debate in the eyes of animal welfare law. The researchers said they found substantial evidence of sentience in crabs, lobsters, crayfish and others. They strongly recommended that these animals receive explicit protection from abuse by UK law.

Recognizing animals as sentient beings

UK Sentience Bill

Government officials in the United Kingdom have been considering some landmark bills that would provide groundbreaking protections to a diverse array of animals. Specifically, the Animal Sentience Bill, would enshrine in law that animals are capable of feelings and emotions, and therefore are entitled to humane treatment. The bill would establish the country’s first Animal Sentience Committee “to scrutinize and report on whether the government is taking into account the adverse effect of any policy on the welfare of animals as sentient beings.”

While there is wide public support for this bill, it is currently in a Parliamentary limbo stage, known commonly as “ping pong,” in which a bill is rapidly sent back and forth between the two chambers before getting passed.

“Sentience” in this bill would be applied to all vertebrates. An early draft of the bill originally left out all invertebrate animals,) implying that any creatures without a backbone are inherently non-sentient. Thanks to the aforementioned research on their sentience, the bill would now recognize the sentience of invertebrates such as crabs, lobsters and octopuses. Unfortunately, these creatures would not receive any specific protections through the Animal Sentience Bill, but they would be considered in future policy-making decisions.

Sentience and animal welfare around the world

Many countries throughout Europe already recognize animal sentience as a legal principle. At the end of last year, Spain reformed its civil code to recognize animals as “living beings endowed with sentience” rather than simply “things,” or “moveable property.” Activists see it as an important first step toward providing the country’s animals with better protections down the line.

In 2019, Australia’s legislative assembly recognized animal sentience for the first time with its Animal Welfare Legislation Amendment Bill. Recognizing that the country’s “domestic animals, livestock, and wildlife” were capable of feeling emotions and pain, the bill laid out a zero-tolerance policy for animal abuse in any form.

While there are some laws against animal cruelty, the federal government in the United States has not passed any legislation recognizing animal sentience. Much of the country’s anti-cruelty regulations change from state to state. Certain states have explicitly recognized the sentience of animals, but others have not.

Respecting all animals

And some animals long thought unable to think or feel pain are gaining new understanding and respect in the scientific community.

Whether it’s farm animals, fish, insects, or lobsters, the research always seems to find that these animals are more cognitively complex than we give them credit for.

It can be difficult to keep up on all the latest findings related to animal sentience. But there’s a surefire way to make sure that we humans are giving all animals the respect they deserve: By leaving all of them off of our plates!

Taking up a plant-based diet is a great first step to avoid engaging in cruelty against sentient beings. Get your free plant-based eating starter kit and be the change for animals today.