Are invertebrates sentient?
Summary
Growing scientific evidence suggests that at least some invertebrates, particularly cephalopods (octopuses, squid, cuttlefish) and decapod crustaceans (crabs, lobsters, crayfish), are likely sentient. The UK became the first country to formally recognize these animals as sentient in law through the Animal Welfare (Sentience) Act 2022.
Supported by 4 cited sources
Key Points
- 1Invertebrates — animals without backbones — represent over 95% of all animal species, yet for most of scientific history they were assumed to lack the capacity for subjective experience.
- 2The report found "very strong evidence" of sentience in octopods and "strong evidence" in true crabs, with "substantial evidence" for squid, cuttlefish, hermit crabs, lobsters, and crayfish.
- 3Decapod crustaceans display motivational trade-offs, accepting greater costs to avoid noxious stimuli — behavior difficult to explain without some form of subjective experience.
- 4The bill received Royal Assent on 28 April 2022, making the UK the first country to formally recognize these invertebrate groups as sentient in national legislation.
Evidence Summary
The question of invertebrate sentience has moved rapidly from the margins of scientific debate to the center of animal welfare policy. That assumption is now being challenged by rigorous evidence, particularly for cephalopod molluscs and decapod crustaceans.
In 2017, philosopher Jonathan Birch of the London School of Economics published "Animal sentience and the precautionary principle" in the journal Animal Sentience (Volume 2, Issue 16), proposing a framework for evaluating sentience evidence. Birch subsequently led a major review commissioned by the UK government: the 2021 report "Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans," produced by a team including Alexandra Schnell, Charlotte Burn, Heather Browning, and Andrew Crump. The team evaluated over 300 scientific studies against eight criteria for sentience.
Key findings included that octopuses demonstrate wound-directed behaviors, learn to avoid locations associated with pain, and show preferences between analgesics.
On the strength of this evidence, the UK amended the Animal Welfare (Sentience) Bill to include decapods and cephalopods. The 2024 New York Declaration on Animal Consciousness further reinforced this direction, stating that empirical evidence indicates "at least a realistic possibility of conscious experience" in many invertebrates.
Supporting Evidence
Sources & Evidence
4 sources cited across 4 claims
Decapod crustaceans display motivational trade-offs, accepting greater costs to avoid...
ObservationalKey findings included that octopuses demonstrate wound-directed behaviors, learn to...
ObservationalIn 2017, philosopher Jonathan Birch of the London School of Economics published...
ObservationalThe 2024 New York Declaration on Animal Consciousness further reinforced this...
Expert Consensus