Monday, April 18, 2016

Which animals are sentient?

Are spiders sentient? I took the above picture of a patient treated by my colleague Dr Stephen Cutter. The presenting complaint was mites. The use of insecticide spray as a treatment clearly had to be avoided.

Most of us assume companion animals have feelings that matter, but to what extent is this true of other animals?

The term “sentience” is usually applied to an individual who has the capacity to experience feelings. The word “feelings” has finally become acceptable in animal welfare science – and not a moment too soon. According to pioneering animal welfare scientist Professor Donald Broom, the reluctance of some scientists to use what they feared were anthropomorphic terms really put the brakes on animal welfare science for a good while:
“When scientists describe a complex system like the brain, terms such as awareness, sentience, welfare, emotion and feeling should be carefully defined and used. If they are not used, important aspects of biological function are missed. The reluctance of some in the scientific community to do this has slowed the development of knowledge.”(Broom, 2016)
According to Professor Broom, a sentient being is one that is able to evaluate the actions of others in relation to itself and other parties; to remember at least some of its own actions and their consequences; to assess risks and benefits of a particular course of action; to have feelings; and to have some degree of awareness.

If you think about it, there may be some human beings (for example, very young or very old humans) who don’t exhibit the above capacities. That is because, Broom says, sentience develops as we develop – and it can also diminish or disappear, for example with age, illness or brain injury.

Whether or not we recognise that an animal is sentient has huge implications in terms of how we treat them. Our attitudes to animals are affected by our evaluations of those animals abilities(Broom, 2010). We can just happen to be very wrong in our assessments.

Which brings us back to our original question, which animals are sentient?

Some people still think sentience is exclusive to humans. That view just isn’t supported by science. As Professor Broom has said, “hardly any ability is uniquely human(Broom, 2015).”

If you’re reading this blog, chances are you’re comfortable that humans and most non-human companion animals like dogs and cats are sentient. They can think, feel and suffer in ways we are generally able to relate to. You may have seen evidence yourself of your dog looking for a toy you’ve hidden, or your cat associating you walking into the kitchen with being fed (examples of learning). They may behave in ways we describe as fearful or sad. In fact, there is a huge body of research supporting the sentience of parrots, dogs, pigs, cattle, sheep and other farm animals, laboratory animals, wild mammals and birds.

Studies have found evidence of learning, awareness and capacity for pain and other feelings in amphibians, fish, cephalopods (this group includes octopus, squid and cuttlefish) and decapod crustaceans (crayfish, crabs and lobsters, for example). There is also evidence of learning and awareness in stomatopod 
crustaceans (e.g. shrimp). (For a recent discussion on cephalopod cognition and consciousness from a philosophical point of view, check out this article by Joshua Shepherd reflecting on the escape of Inky the Octopus from a New Zealand aquarium recently).

Spiders have “substantial cognitive ability” and awareness, and some insects such as bees and ants have a high level of cognitive ability and awareness.
While slugs, snails and swimming sea slugs have clear evidence of a pain system, there is less clear evidence for a pain system in insects and spiders – but the cognitive abilities of insects and spiders exceeds those of slugs, snails and swimming sea slugs.

What does it all mean? Well, we’re not alone in the sentience club. And as more studies come to light, it seems that membership is very broad. Professor Broom argues that this scientific data needs to inform our behaviour:

“All animal life should be respected, and studies of the welfare of even the simplest invertebrate animals should be taken into account when we interact with these animals. Even if we do not protect the animals by law, we should try to avoid cutting an earthworm in half, mutilating a snail, or damaging the wing of an insect.”
Which is why arachnophobes might need one of thesegadgets around the home.

BROOM, D. M. 2010. Cognitive ability and awareness in domestic animals and decisions about obligations to animals. Applied Animal Behaviour Science, 126, 1-11.
BROOM, D. M. Sentience and pain in relation to animal welfare. .  XVII International Congress on Animal Hygiene, 2015 Kosice, Slovakia. International Society for Animal Hygiene.
BROOM, D. M. 2016. Considering animals’ feelings: Précis of Sentience and animal welfare (Broom 2014). Animal Sentience, 2016.005.