Can brainless animals think? | Live Science
Creatures like starfish, jellyfish, sea urchins, and sea anemones don’t have brains, but they can capture prey, sense danger, and respond to their environment.
Does this mean brainless animals can think?
Creatures like jellyfish, sea anemones and hydras have diffuse nerve networks – networks of interconnected neurons spread throughout the body and tentacles, said Tamar Lotanhead of the Laboratory of Cnidarian Developmental Biology and Molecular Ecology at the University of Haifa in Israel.
“The nerve network can process sensory inputs and generate organized motor responses (e.g., swimming, twitching, feeding, and stinging), effectively performing information integration without a brain,” she told Live Science in an email.
This simple setup can support surprisingly advanced behavior. Sprecher’s team showed that the starlet sea anemone (Nematostella vectensis) can form associative memories — learn to link two unrelated stimuli. In the experiment, the researchers trained the sea anemones to associate a harmless flash of light with a mild shock. Finally, the light alone made them retract.
Another experiment showed that sea anemones can learn to recognize genetically identical neighbors after repeated encounters and curb their usual territorial aggression. The fact that anemones change their behavior towards their genetically identical neighbors suggests that they can distinguish between “self” and “non-self”.
A study conducted by Jan Bieleckineurobiologist at the University of Kiel in Germany, showed that box jellyfish can associate visual cues with the physical sensation of hitting objectshelping them navigate obstacles more effectively.
“I deeply believe that learning can be achieved by single neurons,” Bielecki told Live Science in an email.
So if animals with nerve networks instead of brains can remember and learn from their experience, does that mean they can think?
“That’s a tough question to answer,” Sprecher said. The definition of “thinking” depends on the domain. Psychologists, biologists and neuroscientists define “thinking” differently, Bielecki noted.
Additionally, “reflection is too vague a concept,” Bielecki said. Scientists study topics such as decision making, pattern recognition, associative learning, memory formation, and inductive reasoning. Everyone has their own, much narrower definition.
Ken Chengprofessor of animal behavior at Macquarie University in Australia, noted that scientists tend to use the word “cognition” instead of “thought.”
“Scientists avoid the term ‘think’ because thinking, for most of us, means something that goes through the head, and we don’t have a good way to check that in another animal or non-animal species,” Cheng told Live Science. Even “cognition” doesn’t have an agreed-upon definition, he said, but “in the broadest sense, cognition is information processing – using information from the world, including the world inside an organism, to accomplish things.”
If thinking is this broad sense of cognition, then all life forms think, Cheng said. This includes animals like marine sponges and placozoans, which process information on their environment to stay alive. But when it comes to “advanced cognition,” which goes beyond basic learning, scientists aren’t sure whether brainless animals are capable of thinking, Cheng said.
Basic cognition can be thought of as any change in behavior that goes beyond reflexes, Sprecher said. By this definition, brainless animals demonstrate cognition. “However, more advanced types of cognitive abilities might require consciousness or self-awareness,” he said.
Lotan pointed out that cnidarians (an animal family that includes jellyfish, sea anemones and many other marine invertebrates), which evolved more than 700 million years ago, continue to thrive while many animals with brains are long extinct.
“This resilience suggests that they possess a unique adaptive system that allows them to withstand and thrive despite extreme environmental changes over geological time scales – despite lacking a brain,” she said. Their neurons allow them to sense and interpret their environment, “which perhaps represents a rudimentary form of thought.”
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