There is a growing consensus that octopuses are most likely sentient.
Octopuses have intrigued scientists for years, because they have both long- and short-term memory, they remember solutions to problems, and they can go on to solve the same or similar problems. They have been known to climb aboard fishing boats and open holds in search of crabs. They can figure out mazes, open jars, and break out of their aquariums in search of food.
They are obviously acutely intelligent and able to learn novel tasks and orient themselves within their environment, and it has been observed that octopuses apparently dream.
As many researchers and aquarium technicians have noted, octopuses adapt to being captured in a few days, unlike many other animals. The change is from a fearful animal to almost pet-like—friendly and very alert about all that is occurring nearby. Octopuses respond rapidly to rewards and are extremely curious and responsive. They focus on any new object they see.
How do they get so smart?
Complex cognitive abilities, such as causal reasoning, future planning, and mental attribution (an individual’s ability to recognize the thoughts and knowledge of others), are a signal of advanced, higher-order thinking that is usually only observed in vertebrates, rather than animals like snails and mussels. Against all odds, cephalopods produce highly intelligent behaviours that transcend common evolutionary reasoning.
How did a mollusc such as an octopus, a solitary creature with little social life, become so smart? Their body plan and nervous system are so very unlike our own. Rather than having a single central brain where all sensory information and motor controls are processed, they have a partially de-centralized nervous system with nine brains, with smaller brains in each arm. The central brain, which is located between its eyes and contains about 180 million neurons, may simply delegate orders, while the arm is responsible for deciding exactly how to execute the order. The peripheral nervous system is made up of around 300 million neurons.
What do they feel?
It does beg the intriguing question of whether sentience is advantageous for survival in a Darwinian sense and therefore bound or likely to follow, in some shape or form, from having a complex nervous system?
We'll leave you with that to ponder. Here is a little selection of the many videos laying around documenting the intriguing behaviour of these molluscs: