The brains of birds and that of mammals are very different in appearance, but they seem to work in a similar way when considering the higher cognitive capacities of these two groups of animals, suggesting different evolutionary paths for the emergence of a common feature, ie intelligence.
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The brain areas that allow birds and mammals to have high cognitive abilities have a very different structure. However, the types of neurons that form them - also different from the anatomical point of view - are homologous, ie they perform the same function according to the same modalities. University of Chicago scientists have established that "Current Biology" hypothesize that birds and primates have evolved their respective intelligences independently, along evolutionary paths of different brain structures, albeit starting from the same group of cells present in the brain of a very remote common ancestor.
In mammals intelligence is associated with the presence of a large and complex neocortex, that is, a laminar structure that extends over the entire surface of the brain and is composed of six distinct layers. In birds - which may have cognitive abilities that compete with primates, from the use of tools to the ability to recognize themselves in the mirror - this structure is not there; in its place we observe a formation called dorsal ventricular ridge (or DVR), inside which there are large groups of neurons called nuclei. In addition, the neurons of birds are much smaller than those of mammals, and their density in the brain equally higher.
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Steven D. Briscoe and colleagues have discovered that a wide range of neurons of these nuclei form circuits similar to those of the neocortex and that there is a strong resemblance of the neurons of these nuclei with those of mammals. An even more relevant result was obtained by examining the expression profiles of genes in these neurons and by analyzing the transcription factors that control the production of proteins in neurons: the authors found that they are substantially the same. The identity of the genes that are activated indicates that the function of those neurons in the two animal groups is the same. The fact that transcription factors are the same also indicates that the modes of operation are the same. But not only.
Conservation of transcription factors is, in general, a strong indication of a common evolutionary origin. The researchers therefore concluded that the development of the brain structures of birds and mammals, which on the tree of life are located on quite distant branches, developed on two different evolutionary paths, which however led to very similar functional outcomes: the intelligence.