Intelligence Evolved at Least Twice in Vertebrate Animals | Quanta Magazine

A series of studies published in Science in February 2025 provides the best evidence yet that birds and mammals did not inherit the neural pathways that generate intelligence from a common ancestor, but rather evolved them independently.

Avian and mammalian brains display surprisingly similar circuits, the studies found.

The findings could teach us something about how complex circuits in our own brains evolved.

Two new studies used the same powerful tool for identifying cell types, known as single-cell RNA sequencing.

They tracked cells in the palliums of chickens, mice and geckos at various embryonic stages to time-stamp when different types of neurons were generated and where they matured.

They found that the mature circuits looked remarkably alike across animals, just as Karten and others had noted.

Researchers found inhibitory neurons, or those that silence and modulate neural signals, were conserved across birds and mammals.

Similar innovations can evolve multiple times independently.

Octopuses and squids, independently of mammals, evolved camera-like eyes.

Birds, bats and insects all took to the skies on their own.