---
title: "Sentience criteria for animals · Entities · Simulation Hypothesis"
url: https://simulation-hypothesis.com/entities/sentience
description: "The eight criteria from the 2021 review that led UK law to recognise octopuses and crabs as sentient, and what the review found."
license: https://creativecommons.org/licenses/by/4.0/
credit: "Ross Allan Dahl, Simulation Hypothesis (simulation-hypothesis.com)"
---

[Entities](https://simulation-hypothesis.com/entities) › Sentience criteria

# Sentience criteria for animals

In 2021 a team led by Jonathan Birch reviewed the evidence that octopuses, crabs and related animals are sentient, using eight criteria. The report led the UK to recognise them as sentient in law.

1. The animal possesses receptors sensitive to noxious stimuli (nociceptors)
2. The animal possesses integrative brain regions capable of integrating information from different sensory sources
3. The animal possesses neural pathways connecting the nociceptors to the integrative brain regions
4. The animal's behavioural response to a noxious stimulus is modulated by chemical compounds affecting the nervous system (e.g. local anaesthetics, analgesics, opioid-type systems)
5. The animal shows motivational trade-offs, in which the disvalue of a noxious or threatening stimulus is weighed against the value of an opportunity for reward, leading to flexible decision-making
6. The animal shows flexible self-protective behaviour (e.g. wound-tending, guarding, grooming, rubbing) of a type likely to involve representing the bodily location of an injury or noxious stimulus
7. The animal shows associative learning in which noxious stimuli become associated with neutral stimuli, and/or novel ways of avoiding noxious stimuli are learned through reinforcement (habituation and sensitisation do not count)
8. The animal shows that it values a putative analgesic or anaesthetic when injured (e.g. self-administers it, or learns to prefer a location where it is available)

## How the review graded evidence

* **2**: some evidence
* **7-8 criteria at high/very high**: very strong evidence
* **5-6**: strong evidence
* **3-4**: substantial evidence
* **0-1**: sentience unknown or unlikely

## What it found

Very strong evidence of sentience in octopods. Substantial evidence in other coleoids (high confidence for criteria 1, 2, 3 and 7). Strong evidence in true crabs (high or very high for 1, 2, 4, 6 and 7). Substantial evidence in anomuran crabs (high for 1, 2 and 6, medium for 5) and in astacid lobsters and crayfish (high or very high for 1, 2 and 4). Low confidence means the evidence is thin, not that the trait is absent. No group had high confidence of failing a criterion.

| Group                     | 1  | 2  | 3 | 4  | 5 | 6  | 7  | 8  |
| ------------------------- | -- | -- | - | -- | - | -- | -- | -- |
| Octopods                  | VH | VH | H | H  | M | VH | VH | H  |
| Cuttlefish                | H  | VH | H | L  | M | M  | VH | L  |
| Other coleoids (squid)    | H  | VH | H | L  | M | L  | H  | L  |
| Nautiloids                | H  | L  | L | L  | L | L  | M  | VL |
| True crabs (Brachyura)    | H  | VH | L | VH | L | VH | H  | VL |
| Anomuran crabs            | H  | VH | L | L  | M | H  | L  | VL |
| Astacid lobsters/crayfish | H  | VH | L | VH | L | L  | M  | VL |
| Spiny lobsters            | H  | VH | L | L  | L | L  | M  | VL |
| Caridean shrimps          | H  | VH | L | M  | L | M  | L  | VL |
| Penaeid shrimps           | H  | L  | L | M  | L | L  | L  | VL |

VH very high, H high, M medium, L low, VL very low.

## What changed

The UK Animal Welfare (Sentience) Act 2022 (Royal Assent 28 April 2022) recognises animals as sentient and sets up an Animal Sentience Committee. The committee reports on whether government policy pays due regard to animal welfare. After the Birch report, the Lords amended the Bill so that 'animal' includes decapod crustaceans and cephalopod molluscs as well as vertebrates. That covers all cephalopods and decapods, not just octopods and true crabs. https://www.legislation.gov.uk/ukpga/2022/22

Birch J, Burn C, Schnell A, Browning H, Crump A (2021). Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans. LSE Consulting, 19 Nov 2021\. https://www.lse.ac.uk/business/consulting/assets/documents/Sentience-in-Cephalopod-Molluscs-and-Decapod-Crustaceans-Final-Report-November-2021.pdf (read directly)