The Mind Of A Grasshopper
We were all once invertebrates. Whether human or snail, we share a common evolutionary ancestor. In the modern Linnaean system of classification, invertebrate animals are extremely diverse. They include mollusks (snails, slugs, clams, octopuses, squid), arthropods (grasshoppers, dragonflies, lobsters), and arachnids (spiders, tarantulas). Despite this incredible variety, they are classified into a single group and mostly denied welfare protections. Indeed, research sponsors encourage scientists to experiment with these animals rather than vertebrates, to promote more “ethically sound” research.
The situation is improving for some cephalopods such as octopuses, squid, and cuttlefish. Beliefs about sentience in these animals is evolving and they are now considered honorary vertebrates. Some regulatory entities in the E.U. and U.S. are even recognizing welfare considerations for them. In contrast, the U.S. federal government still considers all invertebrates “dissective tissue”. Most other arthropods such as insects, arachnids, and crustaceans — despite the presence of a central nervous system and behavioral flexibility — are not viewed as sentient and thus not worthy of moral status.
The authors posit four reasons for the current exclusion of most invertebrates from science policy and ethical considerations:
- Invertebrates have historically been assigned a lower position in the evolutionary hierarchy.
- We assume that smaller brains must not support cognition or sentience.
- We often feel disgust towards these creatures.
- In the case of invertebrates, science fails to properly balance uncertainty against moral risk. These biases are especially acute for arthropods.
There is no scientific consensus on what constitutes a life that matters. Yet philosophers agree that if a life can go well or poorly, that life has a welfare interest. Only by assuming that invertebrates don’t have lives that can be good or bad can we conclude that they have no welfare interest. In that case, we can exploit them at will. But if invertebrates do have some form of mental life, they may have a morally protectable interest.
So, do they have such a mental life?
We can’t just assume that brain size drives mental capacity because science doesn’t have the data to support this conclusion. Researchers need to examine what small neural networks can do and how brain structure supports mental activities. These cognitive processes are reflected in behavior. For instance, honeybees can learn abstract concepts and communicate them to other bees, and there is even evidence of causal reasoning. Ants seem to pass the self-recognition test, which human babies only do at 20 months of age. Flies, cockroaches, jumping spiders, and other insect orders also display behaviors suggestive of flexible learning. All these behaviors are consistent with thinking.
Felt experience and emotional capacities, described as phenomenal consciousness in humans, are other components of sentience. Invertebrates don’t have similar brain structures that give rise to subjective states of being. Yet there is experimental evidence that they respond emotionally to environmental stimuli with positive or negative behaviors. Scientists vigorously debate the existence of pain perception in invertebrates. They do not seem to have the anatomical structures needed to feel pain, but they behave as if they do. Research has shown that they exhibit behaviors such as responsiveness to analgesics and anesthetics, grooming injured body parts, and a reduction in grooming when pain relief is applied to the injury. But insects may continue normal behaviors in the face of disabling injury, so their response to the perception of pain is unclear.
It’s important to distinguish between pain perception as we understand it, and the broader concept of suffering. This may include stress, frustration, and other unpleasant states that arise from an inability to fulfill one’s desires. And, regardless of the evidence, we still may find many invertebrates arouse feelings of disgust in us. It’s hard to feel empathy for clams, octopuses, ants, or spiders because they seem so alien. But whether or not an organism can feel pain, if it demonstrates through flexible behavior that it is able to learn, that is a strong argument for sentience and thus a claim to moral standing.
Comparative cognition research is notoriously difficult. To avoid false positives, scientists tend to underestimate cognitive capacities. Brain homology, or similarity in structure between species, is not a reliable guide to sentience since we don’t know what configurations to look for. Ethically, erring on the side of false positives is preferable because underestimating an animal’s sentience has the potential to increase suffering. Proposals that call for an assumption of sentience if there is credible evidence for it in at least one species of an order, or if denying sentience would cause serious negative welfare outcomes, are a good first step.
For animal advocates, this paper provides an opportunity to learn more about what it means to be sentient. If we grant moral standing to some invertebrates, that does not obligate us to treat them as equal to vertebrates. What constitutes harm to humans may not be harm to certain sentient animals, yet we need to be consistent in our moral treatment of both vertebrates and invertebrates. The same standards of evidence and risk management that underpin policy protections for vertebrates support extending moral consideration towards certain invertebrates.