For decades, scientists believed social complexity drove brain evolution. The social brain hypothesis held that larger brains evolved to manage larger, more complex social groups.
But new research on cephalopods suggests a different story. Octopuses, squid, and cuttlefish have large brains relative to their body size, yet many are solitary and even cannibalistic.
A new study in iScience analyzed brain size across 79 cephalopod species. The findings show habitat, not sociality, is the key factor.
Cephalopods living on the sea floor in shallow, complex environments had larger brains. These habitats offer abundant food and challenging landscapes that reward learning and problem-solving.
Meanwhile, social cephalopods like squid did not show the expected brain-size increase with sociality. This contradicts the social brain hypothesis.
The research supports the cultural brain hypothesis. Brains may evolve primarily to store and manage information learned through experience, whether social or not.
As researcher Michael Muthukrishna notes, "Solitary animals could evolve large brains if their environment was rich and complex enough to reward learning."
This work reveals multiple evolutionary paths to intelligence, challenging the long-standing social brain dogma.