Scrutinising the science of animal sentience

Sentience is a slippery concept.

As a technical definition, it’s not hard to get your head around – it simply refers to the ability of a being to feel things beyond the immediate sensory environment, experiencing emotions such as joy and contentment, as well as pain and fear.

The difficulty arises in finding evidence of such intangible states in creatures that can’t tell us about their inner lives. While we might intuitively believe that our dog is joyful when we return home at the end of a long day, or that our cat is disdainful of the new brand of cat food on offer tonight, we draw these conclusions from circumstantial evidence. Our intimacy with our domesticated friends leads us to believe we can read their emotional states. But how do you go about proving it? And the issue gets stickier when we start to look further from home. Do monkeys have complex emotions? What about octopus? Insects?

In a Perspective piece published in Science, researchers Frans de Waal and Kristin Andrews scrutinise the current state of play in the science of animal sentience, and the potential repercussions of recognising emotions on our own moral and ethical frameworks.

They describe the long history of debate surrounding the issue, pointing to significant changes in scientific perspective that we now simply take for granted.

“When the medical community recognized infant pain in the 1980s, it was because the evidence was so overwhelming that physicians could no longer act as if infants are immune to pain,” they explain.

“A similar point is being reached where invertebrates can no longer be treated as if they only have a nociceptive response to harmful stimuli.”

We may think of emotions as invisible, but they do in fact leave tell-tale signs that can be measured. Hormones such as oxytocin and cortisol, respectively associated with feelings of pleasure and stress, can easily be determined, and are virtually identical across the gamut of complex life – all the way from humans to invertebrates.

But despite this objective continuity, the interpretation of shared physical markers remains inherently subjective. Until an octopus can tells us directly of its emotional state of being, we will necessarily working from an imperfect dataset.

De Waal explores this uncertainty in his 2019 book on the subject of animal sentience, writing that “anyone who claims to know what animals feel doesn’t have science on their side. It remains conjecture.”

Describing the connection of emotional states in animals to the physical biomarkers known in humans as a “leap of faith”, he stresses that “this is not necessarily bad,”, and that he is “all for assuming that species related to us have feelings.”

It is not unheard of in science to work from such a standpoint – sometimes we know we need to fill in the blanks based on logical assumptions. Consider the uncertainties surrounding the formation of the universe as a key example.

But affording animals the status of sentience has such immediate repercussions in the way we interact with the world around us that the field is generally held to a much higher evidentiary standard. In their discussion, de Waal and Andrews explore the ways that society has conveniently denied a detailed exploration of animal sentience to enable our long history of reliance on animal exploitation, and the implications of taking a new perspective.

“Although we are used to thinking about how our actions affect other humans, recognizing widespread animal sentience requires us to also notice – and consider – our impact on other species,” they write.

“This way, animal sentience is bound to complicate an already complex moral world.”