First of all, it is my mistake—in the paper they used pain more like a synonym to suffering. They wanted to clarify that the animal avoids tissue damage (heat, punching, electric shock etc.) not just on the place, but learns to avoid it. To avoid it right there is simply nociception that can be seen in many low-level animals.
I don’t know much about the examples you mentioned. For example, bacterias certainly can’t learn to avoid stimuli associated with something bad for them. (Well, they can on the scale of evolution, but not as a single bacteria).
First of all, it is my mistake—in the paper they used pain more like a synonym to suffering. They wanted to clarify that the animal avoids tissue damage (heat, punching, electric shock etc.) not just on the place, but learns to avoid it. To avoid it right there is simply nociception that can be seen in many low-level animals.
I don’t know much about the examples you mentioned. For example, bacterias certainly can’t learn to avoid stimuli associated with something bad for them. (Well, they can on the scale of evolution, but not as a single bacteria).