Do single-cell organisms have intelligence? Slime mould, for one, can solve a maze and find food.
It is a common insult in Japan to hear someone ridiculed as "one-cellular," indicating minimal mental capacity. But this putdown may lose some of its bite in the future, because our research has demonstrated that slime mould, a giant unicellular organism with multiple nuclei, is able to solve a maze and similar problems.
The mould is an aggregate of viscous materials called protoplasm. While it lacks a nervous system, legs or eyes, it is still able to move its mass to find food.
Is slime mould intelligent? Let us suppose that biological phenomena are physical phenomena. In biology, these purely physical phenomena are often labelled "functions", and their biological significance debated. However, function seems to be a concept that comes about only when a purpose has been ascribed to a specific physical phenomenon. If a physical phenomenon appears and contributes to the accomplishment of a purpose, that phenomenon is considered functional.
As the highest purpose of a living thing is survival, a living organism can be considered to constitute a survival mechanism. There are many physical phenomena that have not survived over the earth's history, and those around us represent only the survivors. There are reasons for these systems having survived, and the study of these survival mechanisms is central to biology.
Can something with no consciousness be considered intelligent? We need to define what is meant by the use of the term "intelligence", which I will attempt to do here. Humans have consciousness, we are aware of ourselves. This is generally what we call "mind".
Next, let us consider the unconscious world, a world that has a great deal of influence on the consciousness. We have only to consider our own internal information-processing mechanisms to understand that most of them take place on an unconscious level. I doubt anyone could explain how their body maintains balance when they ride a bicycle. While we are riding, our body naturally performs the calculations required to solve the equation. It would be quite difficult for us to clearly define these on the conscious level.
I believe that such unconscious information-processing mechanisms exist in all living things. Is this kind of information processing to be considered intelligence? If we can answer these questions, we should be able to answer the question as to whether or not single-celled animals possess intelligence. It is my goal to research and clarify these unconscious information-processing mechanisms. In this effort, I consider the slime mould to be a most important subject.