And this is how you can tell that whatever designed living organisms was not an intelligent designer, because whatever it is, it keeps designing different solutions to the same problems. For instance, having designed the basic vertebrate nervous system to have a brain at one end and a cord running through the spinal column, it would have used the same starting components when it came to giving some of those vertebrates the intelligence to make tools, solve puzzles and plan ahead.
Not so creationism's intelligent designer.
Like an amnesiac it seems to have forgotten whichever solution it designed first for the three vertebrate orders in which intelligence is to be found - birds, reptiles and mammals. Starting with the ancestral reptilian brain, the design process has produced two different ways of producing the pallium (the part of the brain responsible for cognition, learning and memory recall) in birds and mammals.
Explain the function of the pallium, a structure in the brain responsible for cognition and believed to be common to reptiles, birds and mammals, please. The pallium is a critical structure in the vertebrate brain, involved in cognition, sensory processing, and decision-making. It is believed to be homologous across reptiles, birds, and mammals, meaning it shares a common evolutionary origin.It had been assumed that bird and mammal intelligence had evolved in much the same way, having started from the same starting point, but that view has now been refuted by a team led by Dr. Fernando García-Moreno, Ikerbasque researcher at the Achucarro Basque Center for Neuroscience and the University of the Basque Country (UPV/EHU), along with collaborators. In two studies published in Science they have revealed that birds, reptiles, and mammals have developed complex brain circuits independently, despite sharing a common ancestor. As Campusa, the University of the Basque Country magazine, explains:
Structure and Evolutionary Significance
The pallium is part of the forebrain (telencephalon) and varies in structure across different vertebrate groups:Function
- In mammals, it develops into the cerebral cortex, which is responsible for complex cognitive functions like reasoning, problem-solving, and planning.
- In birds, it forms the avian pallium, which lacks the layered neocortex of mammals but still supports advanced cognitive abilities (e.g., tool use, problem-solving, and episodic memory).
- In reptiles, it is less developed but still contributes to sensory integration and learning.
The pallium plays a role in:Convergent Evolution of Intelligence
- Cognition – Higher-order thinking, problem-solving, and learning.
- Memory Processing – Similar to the mammalian hippocampus, certain parts of the avian and reptilian pallium are involved in spatial and episodic memory.
- Sensory Integration – Processing information from different sensory modalities.
- Decision-Making – Evaluating and selecting actions based on past experiences and current stimuli.
Despite structural differences, the pallium enables similar cognitive abilities in birds and mammals. For example:The pallium exemplifies how different evolutionary paths can lead to comparable cognitive functions, supporting the idea that intelligence is not unique to mammals but rather a broadly evolved trait in vertebrates.
- Corvids and parrots, despite lacking a neocortex, exhibit intelligence comparable to great apes.
- Reptiles, particularly certain lizards, show signs of learning and problem-solving.
Birds Have Developed Complex Brains Independently from Mammals
Science publishes two studies led by an Ikerbasque researcher at Achucarro Basque Center for Neuroscience and UPV/EHU that reveal their unique evolution
Two studies published in the latest issue of Science, led by Dr. Fernando García-Moreno, Ikerbasque researcher at the Achucarro Basque Center for Neuroscience and the University of the Basque Country (UPV/EHU), along with collaborators, have revealed that birds, reptiles, and mammals have developed complex brain circuits independently, despite sharing a common ancestor. These findings challenge the traditional view of brain evolution and demonstrate that, while comparable brain functions exist among these groups, embryonic formation mechanisms and cell types have followed divergent evolutionary trajectories.
The pallium is the brain region where the neocortex forms in mammals, the part responsible for cognitive and complex functions that most distinguishes humans from other species. The pallium has traditionally been considered a comparable structure among mammals, birds, and reptiles, varying only in complexity levels. It was assumed that this region housed similar neuronal types, with equivalent circuits for sensory and cognitive processing. Previous studies had identified the presence of shared excitatory and inhibitory neurons, as well as general connectivity patterns suggesting a similar evolutionary path in these vertebrate species. However, the new studies have revealed that, although the general functions of the pallium are equivalent among these groups, its developmental mechanisms and the molecular identity of its neurons have diverged substantially throughout evolution.
The first study, conducted by Eneritz Rueda-Alaña and Fernando García-Moreno at Achucarro, with the support of a multidisciplinary team of collaborators from the Basque research centers CICbioGUNE and BCAM, the Madrid-based CNIC, the University of Murcia, Krembil (Canada), and Stockholm University, shows that while birds and mammals have developed circuits with similar functions, the way these circuits form during embryonic development is radically different.
Their neurons are born in different locations and developmental times in each species, indicating that they are not comparable neurons derived from a common ancestor.
Dr. García-Moreno, Corresponding author.
Achucarro Basque Center for Neuroscience
University of the Basque Country (UPV/EHU), Leioa, Spain.
Using spatial transcriptomics and mathematical modeling, the researchers found that the neurons responsible for sensory processing in birds and mammals are formed using different sets of genes.
The genetic tools they use to establish their cellular identity vary from species to species, each exhibiting new and unique cell types.
[This all indicates that these structures and circuits are not homologous, but rather the result of convergent evolution, meaning that] they have independently developed these essential neural circuits through different evolutionary paths.
Dr. García-Moreno.
The second study further explores these differences. Conducted at Heidelberg University (Germany) and co-directed by Bastienne Zaremba, Henrik Kaessmann, and Fernando García-Moreno, it provides a detailed cell type atlas of the avian brain and compares it with those of mammals and reptiles.
We were able to describe the hundreds of genes that each type of neuron uses in these brains, cell by cell, and compare them with bioinformatics tools.
Dr. García-Moreno.
The results show that birds have retained most inhibitory neurons present in all other vertebrates for hundreds of millions of years. However, their excitatory neurons, responsible for transmitting information in the pallium, have evolved in a unique way. Only a few neuronal types in the avian brain were identified with genetic profiles similar to those found in mammals, such as the claustrum and the hippocampus, suggesting that some neurons are very ancient and shared across species.
However, most excitatory neurons have evolved in new and different ways in each species.
Dr. García-Moreno.
The studies, published in Science, used advanced techniques in spatial transcriptomics, developmental neurobiology, single-cell analysis, and mathematical modeling to trace the evolution of brain circuits in birds, mammals, and reptiles.
Rewriting the Evolutionary History of the Brain
Our studies show that evolution has found multiple solutions for building complex brains. Birds have developed sophisticated neural circuits through their own mechanisms, without following the same path as mammals. This changes how we understand brain evolution.
Dr. García-Moreno.
These findings highlight the evolutionary flexibility of brain development, demonstrating that advanced cognitive functions can emerge through vastly different genetic and cellular pathways.
The importance of studying brain evolution
Our brain makes us human, but it also binds us to other animal species through a shared evolutionary history,
Dr. García-Moreno.
The discovery that birds and mammals have developed neural circuits independently has major implications for comparative neuroscience. Understanding the different genetic programs that give rise to specific neuronal types could open new avenues for research in neurodevelopment. Dr. García-Moreno advocates for this type of fundamental research:
Only by understanding how the brain forms, both in its embryonic development and in its evolutionary history, can we truly grasp how it functions.
Dr. García-Moreno.
Publications:
Rueda-Alaña E, Senovilla-Ganzo R, Grillo M, Vázquez E, Marco-Salas S, Gallego-Flores T, Ftara A, Escobar L, Benguría A, Quintas A, Dopazo A, Rábano M, dM Vivanco M, Aransay AM, Garrigos D, Toval A, Ferrán JL, Nilsson M, Encinas JM, De Pitta M, García-Moreno F (2025). Evolutionary convergence of sensory circuits in the pallium of amniotes
Science DOI: 10.1126/science.adp3411.
Zaremba B, Fallahshahroudi A, Schneider C, Schmidt J, Sarropoulos I, Leushkin E, Berki B, Van Poucke E, Jensen P, Senovilla-Ganzo R, Hervas-Sotomayor F, Trost N, Lamanna F, Sepp M, García-Moreno F, Kaessmann H (2025).
Developmental origins and evolution of pallial cell types and structures in birds
Science DOI: 10.1126/science.adp5182
Structured AbstractThe thing about evolution where no intelligence, no foresight and no plan is involved is that it proceeds on its own trajectory as major taxon's evolve, converging on similar solutions by different routes when there is environmental pressure driving it. The outcome is adaptation to the prevailing environment arrived at from different directions.
INTRODUCTION
For decades, scientists have debated the homologies between the mammalian neocortex and the pallium of other vertebrates. Claims of homology are often based on gene expression patterns in embryonic brains or neuronal connectivity patterns in adult brains. We sought to understand pallial evolution because its homologies provide insights into the evolutionary and developmental pathways of brain structures across species.
RATIONALE
We tackled this debate from alternative perspectives by investigating the developmental formation of pallial circuitry through neurogenic, transcriptional, and mathematical analyses in three selected species: chick, mouse, and gecko. By examining the development of their pallial circuits, we aimed to determine whether similarities in sensory processing circuits are due to conserved homology or convergent evolution.
RESULTS
Our study revealed that neurons that form the three stations of the pallial circuit are generated at different times and in distinct brain regions across species. The avian dorsal ventricular ridge (DVR) circuit develops in a different order than the neocortical circuit, whereas the avian hyperpallial circuit follows previously unknown neurogenic rules that are not seen in either the avian DVR or the mouse neocortex. Geckos exhibit a dual sequence: Their dorsal circuit forms like the mammalian neocortex, whereas their ventral circuit develops like the avian DVR. These findings indicate unexpected diversification in amniote pallial sensory circuit developmental programs.
On the molecular level, single-cell RNA sequencing depicted different evolutionary trends for equivalent cell types, produced in homologous pallial regions and at equivalent neurogenic times. Glutamatergic pallial neurons mature into divergent neuronal types in chick and mouse, whereas γ-aminobutyric acid–releasing (GABAergic) pallial neurons showed strong conservation, underscoring their fundamental role in pallial sensory circuits. By means of spatially resolved transcriptomic analysis, we inferred the pallial location and transcriptional type of early neurons generated in the pallium of both chick and mouse. This analysis showed greater conservation of GABAergic cells and indicated that the only similarity in the glutamatergic class was mesopallial neurons of the chick brain and deep, lateral mammalian cortical neurons.
The developmental differences were also notable in progenitors and other cells. Whereas pallial radial glial cells displayed similarities between species, their neurogenic behaviors differed markedly. Additionally, the population of intermediate progenitor cells that expanded neuronal numbers in the mammalian neocortex had no clear homolog in the avian developing pallium. Cajal-Retzius cells were not found in the chick pallium. Furthermore, mathematical modeling suggests that components of sensory circuits in birds and mammals were shaped by similar functional constraints.
CONCLUSION
Our study demonstrates that high-order sensory processing circuits have evolved separately in different vertebrate taxa, converging into a functionally similar circuit. The differences in the developmental rules, progenitor cells, and transcriptomic profiles support a nonhomologous character of the amniote pallial circuits. The strong conservation of GABAergic neurons indicates their crucial role in pallial sensory circuits, whereas the divergent development of glutamatergic neurons suggests a flexible evolution of this neuronal class. Evolution tinkered with pallial circuit development, structure, and function. And likely, convergent evolution sculpted the formation of the components of the sensory circuits in amniote species.
Abstract
(Left) Illustrations depicting the varied sequences of neurogenesis found in the pallial circuits of amniotes. (Top right) Spatially resolved transcriptomics allowed us to identify a wide neuronal diversification in the chick pallium. (Bottom right) Single-cell RNA sequencing of early born neurons revealed conservation in the differentiation of GABAergic neurons in amniotes, which contrasted with the diversification of most glutamatergic neurons. DPall, dorsal pallium; Hc, hippocampus; IPCs, intermediate precursor cells; LPall, lateral pallium; SPall, subpallium; Th, thalamus; VPall, ventral pallium.
The amniote pallium contains sensory circuits that are structurally and functionally equivalent, yet their evolutionary relationship remains unresolved. We used birthdating analysis, single-cell RNA and spatial transcriptomics, and mathematical modeling to compare the development and evolution of known pallial circuits across birds (chick), lizards (gecko), and mammals (mouse). We reveal that neurons within these circuits’ stations are generated at varying developmental times and brain regions across species and found an early developmental divergence in the transcriptomic progression of glutamatergic neurons. Our research highlights developmental distinctions and functional similarities in the sensory circuit between birds and mammals, suggesting the convergence of high-order sensory processing across amniote lineages.
Structured Abstract
INTRODUCTION
Some avian species have advanced cognitive abilities that rival those of great apes, likely facilitated by evolutionary innovations in the avian forebrain, including the pallium. The pallium, equivalent to the dorsal telencephalon, has undergone substantial morphological changes during amniote evolution since their last common ancestor ~320 million years ago. In mammals, the pallium primarily includes layered structures such as the isocortex, whereas in birds and reptiles, it mostly comprises the nuclear-organized dorsal ventricular ridge (DVR). Unlike other reptiles, birds lack a layered cortex and instead have another nuclear-organized region, the hyperpallium. Because of these extensive differences, diverse views on amniote pallium evolution exist, some assuming homology of cell types with similar roles in the neural circuitry, and others suggesting homologous developmental territories.
RATIONALE
Recent single-cell molecular studies in adult reptiles and restricted areas of the pallium of songbirds have provided evidence for homology of specific pallial cell types, suggested to originate from shared embryonic regions but diverging considerably in their transcriptomic profiles across amniote lineages. However, cell type–level data for several key regions of the avian pallium, such as the hyperpallium, have been lacking. Moreover, despite the recognized importance of development in understanding evolutionary cell type relationships, the development of the pallium in nonavian reptiles and birds has never been studied at the single-cell level. To explore the developmental origins and evolution of pallial structures and cell types in birds, we generated spatially resolved cell type atlases of the entire adult chicken pallium and across in ovo development using single-nucleus RNA sequencing (snRNA-seq) and spatial transcriptomics technologies and compared them to corresponding atlases from mammals and nonavian reptiles.
RESULTS
We detected conserved expression patterns in inhibitory neurons across amniotes, with an expansion of one cell type in birds, which is predominantly located in the mammalian amygdala but present throughout the avian pallium. We also show evolutionary conservation of excitatory neuron types in the hippocampal regions of amniotes and identify homologs of excitatory neurons in the mammalian claustrum in the avian anterior DVR. Avian cell populations related to claustrum-like neurons resemble neurons in deep layers of the mammalian cortex, challenging current developmental and circuitry-focused hypotheses. Several excitatory neuron repertoires diverged substantially in birds, especially in the hyperpallium and ventral DVR (called the nidopallium). Our findings clarify the borders of the hyperpallium and reveal that only a fraction of cells in this region are homologous to neurons in the mammalian isocortex. Whereas adult comparisons support the functional equivalence of the DVR to the mammalian isocortex, developmental data reveal correspondences of cell types in ventral pallial areas between birds and mammals, illustrating the pronounced gene expression divergences of adult cell types in these regions. We also identify an extensive developmental convergence of gene expression programs between excitatory cell populations from the hyperpallium and nidopallium, accounting for their previously observed similarity in adults. This functional convergence occurs during late developmental stages, suggesting that, in birds, the topological location within the pallium is not always a determinant factor for adult gene expression programs underlying functional properties.
CONCLUSION
Our study provides key insights into the anatomy and development of the avian pallium, paving the way for research on the molecular mechanisms underlying advanced avian behaviors. We elucidate the evolutionary history of the amniote pallium, confirming previous notions and findings, such as the transcriptomic conservation of inhibitory neurons or of excitatory neurons in the hippocampus, while also identifying novel relationships, for example, that of cell populations in the anterior DVR and deep layers of the mammalian isocortex. We also show that adult transcriptomic similarities within the avian pallium may result from developmental convergence rather than reflecting homology. Our work thus emphasizes the need for updated models of amniote pallial evolution and the importance of considering developmental data in evolutionary comparisons. Overall, our study resolves long-standing debates on the amniote pallium, offering valuable insights into the evolutionary trajectory and diversification of neural cell types and structures crucial for advanced behaviors.
snRNA-seq delineates the development and cellular composition of the chicken pallium (left). During development, glutamatergic neuron populations from dorsal and ventral pallial areas converge in their transcriptomic profiles (top right). Comparisons of cell types across all major lineages of amniotes (mammals, birds, nonavian reptiles) in adults and development reveal cell type and potential regional homologies in the pallium. Single and double asterisks indicate external datasets.
Abstract
Innovations in the pallium likely facilitated the evolution of advanced cognitive abilities in birds. We therefore scrutinized its cellular composition and evolution using cell type atlases from chicken, mouse, and nonavian reptiles. We found that the avian pallium shares most inhibitory neuron types with other amniotes. Whereas excitatory neuron types in amniote hippocampal regions show evolutionary conservation, those in other pallial regions have diverged. Neurons in the avian mesopallium display gene expression profiles akin to the mammalian claustrum and deep cortical layers, while certain nidopallial cell types resemble neurons in the piriform cortex. Lastly, we observed substantial gene expression convergence between the dorsally located hyperpallium and ventrally located nidopallium during late development, suggesting that topological location does not always dictate gene expression programs determining functional properties in the adult avian pallium.
An intelligent design process, proceeding according to a plan with a specific objective, and starting from the same starting point, would use the same solution having designed it just once, perfectly fitted for purpose. So, if mammalian and bird intelligence, dependent on the design and function of the brain, had been intelligently designed, we would wee the same structures performing the same functions.
This is not what we see, so we know that intelligence in birds and mammals was not intelligently designed but evolved by a mindless process operating without a plan and simply responding to the selection pressure in the environment.
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