Animal sentience has received little attention by those who have studied the characteristics and capabilities of nonhuman animals. This is unfortunate, because animal sentience is a very important issue. Sentience is what matters when we consider which beings to give moral consideration to. Due to this, we need to study the issues of what physical structures are necessary for sentience, which beings are sentient, and what interests sentient beings may have.
In order to understand these problems there are several questions that must be addressed.
How can we guess whether a certain being is sentient or not? There are several criteria that nonhuman animals satisfy that give us reasons to conclude they are.
Those who deny that animal sentience sometimes claim that it cannot be demonstrated whether animals are sentient. But there are powerful reasons to reject such a view.
Given the criteria we have to consider whether a being is conscious, there are reasons to conclude that animals who are sentient and therefore conscious have centralized nervous systems. The importance of animal sentience is perfectly compatible with this.
There are animals that don’t have the physical structures that are needed in order to have experiences. They include those that lack any nervous system and those whose nervous systems are not centralized.
Most of the animals on our planet are invertebrates. The invertebrate label applies to a hugely diverse range of animals, comprising 99% percent of all species. Such diversity in anatomical structures makes evaluating sentience in invertebrates challenging, and the research is crucial due to the enormous number of individuals who may be sentient and experiencing harms.
Even if we conclude that many nonhuman animals are sentient beings, we may still not be able to recognize situations in which they are suffering. There are several indicators that can help us determine in which cases animal sentience is present, and when animals are suffering.