It turns out that even a single-celled organism may be capable of learning. Scientists have found that an organism devoid of a nervous system can actually learn.
Memory and the ability to learn are both key parts of the animal world. Learning from experiences and adapting behavior are both important for animals that need to deal with the dangerous environment that they live in. With that said, researchers have long thought that single-celled organisms may not have the ability to actually learn.
In this new study, the researchers decided to see if it was possible for bacteria or other single-celled organisms to actually learn. For the purposes of their experiment, the scientists chose to study a protist, also known as a slime mold. This is a giant cell that inhabits shady, cool areas and has been previously shown to be able to solve a maze, avoid traps, and optimize its nutrition.
For the experiment, the researchers challenged different groups of this slime mold with bitter, but harmless, substances that the slime mold needed to pass through in order to reach a food source. The "bridge" was either quinine or caffeine, and a control group needed to cross a "bridge" that wasn't coated with these sources.
The researchers found that the molds were initially reluctant to travel through quinine or caffeine. However, they gradually "realized" that they were harmless substances and then crossed them rapidly. In fact, the researchers found that the slime mold "learned" not to fear the harmless substance after behind confronted with it on several occasions. With that said, the slime mold returned to its initial behavior of distrust after two days without contact with the substance.
In this case, the slime mold was showing a form of habituation, which is rudimentary learning. This form of learning exists in all animals but, until now, has not been seen in a non-neural organism like a slime mold.
The results show that learning is possible for single-celled organisms, in a sense. They can determine what is and is not harmful and then "remember" for a period of time afterward.
The findings were published in the April 27 issue of the journal Proceedings of the Royal Society B: Biological Sciences.
