A recent study has shown that Stentor coeruleus, a trumpet-shaped protozoan measuring about 0.04 inches (1 mm), can learn despite lacking a brain or nervous system. Traditionally, scientists believed that associative learning required some form of neural machinery. However, researchers led by cognitive neuroscientist Samuel Gershman at Harvard University found that these unicellular organisms can exhibit learning behaviors. In experiments, Stentor coeruleus cells were subjected to a series of taps, initially responding by contracting their bodies. Over time, the cells habituated to the taps, indicating a form of learning. When a weak tap was paired with a stronger one, the cells learned to respond to the weaker stimulus alone, demonstrating non-trivial learning capabilities. This research, published in BioRxiv, suggests that the evolutionary origins of learning may be far older than previously thought, potentially existing before the development of complex nervous systems. Gershman noted that the similarities between these single-celled organisms and neurons in more complex brains hint at shared learning mechanisms that may have persisted through evolution.