Introducing the brain: How human compares to birds (Introduction)

by David Turell , Sunday, February 16, 2025, 18:58 (20 days ago) @ David Turell

Both developed differently but comparatively:

https://www.sciencedaily.com/releases/2025/02/250213143301.htm

"New research has revealed that birds, reptiles, and mammals have developed complex brain circuits independently, despite sharing a common ancestor. These findings challenge the traditional view of brain evolution and demonstrate that, while comparable brain functions exist among these groups, embryonic formation mechanisms and cell types have followed divergent evolutionary trajectories.

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"Previous studies had identified the presence of shared excitatory and inhibitory neurons, as well as general connectivity patterns suggesting a similar evolutionary path in these vertebrate species. However, the new studies have revealed that, although the general functions of the pallium are equivalent among these groups, its developmental mechanisms and the molecular identity of its neurons have diverged substantially throughout evolution.

"The first study,...shows that while birds and mammals have developed circuits with similar functions, the way these circuits form during embryonic development is radically different. "Their neurons are born in different locations and developmental times in each species," explains Dr. García-Moreno, head of the Brain Development and Evolution laboratory, "indicating that they are not comparable neurons derived from a common ancestor." Using spatial transcriptomics and mathematical modeling, the researchers found that the neurons responsible for sensory processing in birds and mammals are formed using different sets of genes. "The genetic tools they use to establish their cellular identity vary from species to species, each exhibiting new and unique cell types." This all indicates that these structures and circuits are not homologous, but rather the result of convergent evolution, meaning that "they have independently developed these essential neural circuits through different evolutionary paths."

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"The results show that birds have retained most inhibitory neurons present in all other vertebrates for hundreds of millions of years. However, their excitatory neurons, responsible for transmitting information in the pallium, have evolved in a unique way. Only a few neuronal types in the avian brain were identified with genetic profiles similar to those found in mammals, such as the claustrum and the hippocampus, suggesting that some neurons are very ancient and shared across species. "However, most excitatory neurons have evolved in new and different ways in each species," details Dr. García-Moreno.

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"'Our studies show that evolution has found multiple solutions for building complex brains," explains Dr. 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."

"'These findings highlight the evolutionary flexibility of brain development, demonstrating that advanced cognitive functions can emerge through vastly different genetic and cellular pathways.

"'Our brain makes us human, but it also binds us to other animal species through a shared evolutionary history," explains Dr. García-Moreno. The discovery that birds and mammals have developed neural circuits independently has major implications for comparative neuroscience."

Comment: we are all different in brain structure and function. Humans have HAR regions in their DNA driving our difference. Brain development varies in convergent ways. It seems the drive to evolve is present in every species.