Neurobiologists at the Achucarro Basque Center for Neuroscience of Spain have made revolutionary discoveries. Their push was to look at how intelligence has evolved in vertebrates, particularly birds and mammals. A series of groundbreaking studies published in the journal Science in February 2025 reveal that these two groups evolved complex cognitive abilities independently. This shocking result brings into focus a centuries-old debate over the evolutionary routes that determined the brains of these species.
Fernando García-Moreno, a leading neurobiologist, describes bird brains as “unspecified balls of neurons without landmarks or distinctions.” This characterization exposes the long history of confusion surrounding vertebrate intelligence. It emphasizes the most complex neural architectures—those that have evolved over hundreds of millions of years. This study investigates the avian pallium, the bird analog of the brain, in a detailed manner. It provides surprising new perspectives on how these regions developed over time to improve mental processes.
These studies underscore the power of RNA sequencing in building a precise atlas of the bird pallium. This study highlights how neuronal development can differ drastically between species. These discoveries shine light on the deep shared ancestry between birds and mammals. They have taken radically different routes in their neurobiological development.
Historical Context of Vertebrate Intelligence
That quest to understand how birds and mammals brains evolved very different forms of intelligence has a long legacy. This lizard-like creature, which scientists think is the common ancestor of both groups, lived about 320 million years ago. It is from this ancestor that they inherited these complex neural pathways, which would one day gave rise to our higher order cognitive functions.
Harvey Karten’s groundbreaking work in the 1960s was a watershed moment for neuroanatomy. He carefully traced brain pathways in various animals, like pigeons, owls, and chickens. His work offered important perspectives on the difference between avian and mammalian neural structures.
Güntürkün acknowledges Karten’s impact on the field, stating, “Karten’s 1969 paper changed the discussion in the field of neuroanatomy.” Not all researchers were convinced by Karten’s verdict. Luis Puelles, a Spanish anatomist, made some fascinating inferences regarding the evolution of vertebrate palliums. His conclusions ignited passionate debate among the scientific community.
Recent Findings on Neural Development
García-Moreno’s research seeks to connect these two worlds by studying the pallium region in several different species. Tackling the pursuit of neural development with Bastienne Zaremba and her crew at Heidelberg University, he took a deep dive into the subject. Through a small collaborative study, they undertook to understand better the transformations of the avian and mammalian brains. Though they had developed independently, both groups were contending with the same environmental scenarios.
Zaremba’s research has found an absolutely mind-blowing phenomenon. Now researchers have discovered that pallial neurons in these developing birds can still become specialized—like those in adult brains—regardless of where they came from during development. This plasticity, in a way, underscores a previously unrecognized flexibility in vertebrate brain evolution.
She elaborated on this finding: “How we end up with similar circuitry was more flexible than I would have expected.” This remarkable flexibility, in turn, begs fascinating questions about how various species can all come to similar solutions to the same cognitive obstacles.
The experiments revealed that birds and mammals indeed possess the same basic circuitry within their avian neocortex and mammalian DVR. Their neuronal compositions are quite different. This means that different evolutionary trajectories can result in similar cognitive products.
Implications of Independent Evolution
The policy implications of these findings go further than just academic intrigue. Most importantly, they challenge anthropocentric assumptions about the nature of intelligence and the developmental trajectories that lead to intelligence across vertebrates. As Bradley Colquitt notes, “It allows you to say: What are the different neural solutions that these organisms have come up with to solve similar problems of living in a complex world and being able to adapt in a rapidly changing terrestrial environment?”
García-Moreno is careful to note that these similarities do not mean that vertebrates are all on the same trajectory toward intelligence. He remarked, “Both of them were right; none of them was wrong,” referring to the contrasting views held by Karten and Puelles. He further explained that “there’s limited degrees of freedom into which you can generate an intelligent brain, at least within vertebrates.”
The idea that intelligence might emerge via very different evolutionary pathways adds another layer to the strangeness of life on Earth. Güntürkün highlighted this by stating, “A bird with a 10-gram brain is doing pretty much the same as a chimp with a 400-gram brain.” Taken together, these comparisons indicate that brain size is not the sole determinant of cognitive skills. Rather, these differences in structural and functional adaptions between each species are what consistently decide their fate.
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