It has been shown that the brains of birds and mammals evolved in different ways

Two papers published in the journal Science have made it clear that birds, reptiles and mammals, although they have evolved from a common ancestor, have independently developed complex brain circuits. These findings have highlighted the evolutionary flexibility of brain development, demonstrating that advanced cognitive functions can manifest themselves through very different cellular and genetic pathways.

In the first, a specific area of the brain, pallium has been studied and it has been observed that although the general functions of pallium in mammals, birds and reptiles are equivalent, the mechanisms of neuronal development and molecular identity have diverged significantly during evolution. Pallium, specifically, the area of the brain where the mammalian neocortex develops, which is responsible for complex cognitive functions, and the area that most distinguishes humans from other species.

Until now, the researchers believed that the difference between different groups of animals was in the complexity of pallium, but that they had similar types of neurons and similar circuits for sensory and cognitive processing.

Now, however, through spatial transcriptomic analysis and mathematical modeling, researchers have shown that neurons responsible for sensory processing in birds and mammals are formed using different groups of genes. This is an example of convergent evolution.

The second study delves into these differences by compiling a detailed atlas of brain cell types in birds and comparing them to those in mammals and reptiles. Thus, they have observed that birds have preserved most of the inhibitory neurons found in other vertebrates since hundreds of millions of years ago. In contrast, the excitatory pallial neurons responsible for transmitting information have been shown to have evolved differently. In some ways, birds have used their own mechanisms to develop sophisticated neural circuits without following the same mammalian pathway. Researchers have recognized that this has changed the way they understand the evolution of the brain.

In both studies, the Ikerbasque researcher Fernando García Moreno, from the Achucarro centre and the UPV/EHU, has participated, together with several international researchers from different centres in the Basque Country (Achucarro, CICbioGUNE, BCAM...).