Bird brains evolved independently from mammals, surprising study finds

LEIOA, Spain — New research is turning our understanding of brain evolution on its head. Scientists have discovered that birds developed their complex brain circuits independently from mammals, rather than inheriting them from a shared ancestor.

For years, scientists debated whether the sophisticated neural networks in bird and mammal brains originated from a common ancestor. This new study, published in Science, provides strong evidence that they evolved separately, following distinct developmental pathways.

The study, led by researchers at Spain’s Achucarro Basque Center for Neuroscience, reveals that birds and mammals each found their own way to build advanced brain circuits. These circuits, responsible for processing sensory information like sight and sound, perform similar functions but emerged through independent evolutionary paths over millions of years.

“Our brain makes us human, but it also binds us to other animal species through a shared evolutionary history,” explains Dr. Fernando García-Moreno, who led the research. His team studied brain development in chickens, mice, and geckos to understand how these neural circuits form during early growth stages.

The study focused on the pallium, a brain region that develops into the neocortex in mammals—the wrinkled outer layer responsible for complex thinking, sensory processing, and decision-making. Previously, scientists assumed the pallium followed similar developmental patterns in birds and mammals, just with different levels of complexity. However, this research shows that assumption was incorrect.

Using advanced technology to track brain development, the researchers discovered that nerve cells in birds form at different times and in different brain regions compared to mammals. They tracked the formation of neural circuits from their earliest stages using techniques that allowed them to see individual cells and their genetic activity.

Interestingly, when studying geckos, the team found a mixed pattern: part of the reptilian brain develops like that of mammals, while another part develops more like birds. This suggests that evolutionary pressures can lead to different solutions for building similar brain functions.

A key finding of the study involved two types of brain cells: excitatory neurons, which transmit signals, and inhibitory neurons, which regulate brain activity. While inhibitory neurons remained highly conserved across all species studied, excitatory neurons evolved in unique ways. This suggests that while some core components of brain circuitry stayed the same, others were free to diverge along separate evolutionary paths.

A complementary study from Heidelberg University further explored these findings by creating a detailed cell atlas of the avian brain. This research, also published in Science, confirmed that while birds have maintained many ancient neuron types, they also evolved unique variations. Only a few neuronal types in the avian brain showed genetic profiles similar to those found in mammals, mainly in regions like the claustrum and hippocampus, suggesting that some neurons have deep evolutionary roots shared across species.

“Our studies show that evolution has found multiple solutions for building complex brains,” explains García-Moreno. “Birds have developed sophisticated neural circuits through their own mechanisms, without following the same path as mammals. This changes how we understand brain evolution.”