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Two groundbreaking studies published in the journal Science challenge established ideas about the evolution of the vertebrate brain, demonstrating that birds and mammals have developed complex cognitive abilities in unique, independent pathways.
Research led by Fernando García-Moreno from the Basque Center for Neurology Achucarro and the UPV/EHU reveals that pallium — a key brain region responsible for higher cognitive functions — was formed by different molecular mechanisms in different vertebrate groups. These discoveries fundamentally change our understanding of the evolution of the brain and neural circuits.
The results demonstrate that nature has devised different ways to form complex brain structures, using different sets of genes and developmental mechanisms. This demonstrates the power of convergent evolution in shaping similar functional systems through different genetic pathways.
Rethinking the development of the pallium
The pallium is a brain region that in mammals develops into the neocortex, which is responsible for cognitive functions and complex behavior. Traditionally, the pallium of birds, reptiles, and mammals was thought to contain similar types of neurons and equivalent neural circuits that evolved from a common ancestor.
New research refutes this theory, showing that while the pallium performs similar functions in these animal groups, its development and molecular identity have diverged significantly over the course of evolution.
The first study, conducted by Eneritz Rueda-Alanya and Fernando García-Moreno, together with an interdisciplinary team of scientists, revealed significant differences in the formation of neural circuits between birds and mammals.
“Their neurons are born in different places and at different times in development in each species,” — explains Dr. Garcia-Moreno, emphasizing that these cells do not originate from a common ancestor, as previously thought.
Molecular and genetic differences
Using advanced spatial transcriptomics and mathematical modeling techniques, researchers have discovered that neurons responsible for sensory information processing are formed by different sets of genes in birds and mammals.
The second study, conducted at Heidelberg University under the leadership of Bastien Zaremba, Henrik Kessmann and Fernando García-Moreno, presents a detailed atlas of avian brain cell types and compares it with mammalian and reptilian cells.
The results reveal a surprising picture: Birds have retained most of the inhibitory neurons common to all vertebrates over hundreds of millions of years of evolution. However, their excitatory neurons, responsible for transmitting information in the pallium, have evolved in a unique way.
Preservation of ancient neural structures
Interestingly, researchers have identified several types of neurons in the bird brain with genetic profiles similar to those found in mammals. These similar neurons are found in structures such as the claustrum and hippocampus, suggesting their ancient origin and conservation across species.
“However, most excitatory neurons evolved in new and different ways in each species,” — emphasizes Dr. Garcia-Moreno, pointing to the significant divergence of evolutionary paths.
Significance for neuroscience and evolutionary biology
These discoveries have important implications for our understanding of brain evolution and cognitive abilities. They demonstrate the evolutionary flexibility of brain development, showing that complex functions can arise through different genetic and cellular pathways.
Understanding the different genetic programs that lead to the emergence of certain types of neurons could open new avenues for neurodevelopmental research and possibly help in the development of new approaches to treating neurological disorders.
Dr. Garcia-Moreno emphasizes the importance of basic research in this field:
