According to recent studies, avian and mammalian brains differ entirely in embryological development and cellular structure despite sharing comparable cognitive functions.
Challenging the Linear Path of Vertebrate Evolution
For decades, the scientific consensus held that brain evolution among vertebrates followed a single, linear progression toward increasing complexity. Scientists largely assumed that mammals and birds inherited similar neural circuits from a shared ancestor, with variations appearing only in the degree of sophistication across different species. That traditional framework has now been upended by fresh scientific inquiry into the pallium, a brain region critical for advanced cognitive functions.
In mammals, the pallium gives rise to the neocortex, which governs memory, reasoning, and decision-making. However, new investigations reveal that this apparent resemblance is fundamentally misleading.
Recent breakthroughs stem from two complementary studies utilizing advanced technologies such as spatial transcriptomics, single-cell analysis, and mathematical modeling to map neuronal development. The first of these investigations focused on embryonic brain development and discovered that pallium neurons emerge at entirely different times and locations in birds compared to mammals.
Their neurons naissent à des stades de développement distincts. Dr. Fernando García-Moreno
As explained by Dr. Fernando García-Moreno—whose work with chicken embryos involved experimental manipulation—avian and mammalian neurons are born at distinct developmental stages. This timing proves that these neurons do not trace back to a shared ancestor but instead evolved independently. Furthermore, the genes driving neural circuit formation differ between the two groups, indicating that each lineage forged a unique genetic pathway to construct its brain.
Cellular Divergence Across Birds, Mammals, and Reptiles
The second study explored brain cell types across birds, mammals, and reptiles through deep single-cell analysis, mapping the genes expressed by individual neurons. The findings demonstrate that while birds retained certain inhibitory neurons common to all vertebrates, their excitatory neurons—which are vital for information processing—evolved independently from those of mammals.
Aside from a few isolated similarities found specifically within the hippocampus and the claustrum, the vast majority of neurons diverge significantly between the two groups. This cellular divergence strongly suggests that avian and mammalian brains are not homologous structures. Instead, they arrived at functionally similar cognitive architectures through evolutionary convergence rather than shared ancestry.
Redefining Intelligence Beyond Mammalian Brains
These discoveries shed new light on why certain birds can match primates in intelligence despite possessing entirely different cerebral architectures.
