Recent studies have shown fascinating proof that birds and mammals evolved smartness on their own. This conclusion directly disputes the long-held idea that they are on the same neural pathway. New research from our lab and others published in the journal Science have begun to unravel a very fine-structured evolution of brain circuits. Together, these studies particularly illuminate the songbird pallium and the mammalian neocortex.
The research builds on pioneering studies led by scientists such as Harvey Karten. His groundbreaking paper in 1969 changed the paradigm on avian intelligence. Karten’s comparative work on the brain circuits of mammals and birds, including pigeons and owls, has been pivotal in reshaping how scientists view bird cognition. This new science substantiates Karten’s pioneering work. It further highlights how differently intelligence has evolved along different vertebrate lineages.
Transformative Contributions to Avian Intelligence Research
In the 1960s, Harvey Karten, a pioneer of comparative neuroscience, was doing important research that mapped the brain circuits of various species. His research established avian intelligence as an exciting new frontier. His investigations into how these circuits operated in birds compared to mammals uncovered key differences that had been mostly ignored.
Karten’s pioneering efforts laid the groundwork for additional exploration into avian neural circuits, but most importantly, changed the scientific community’s perception of bird intelligence. Notable studies involving Alex, an African grey parrot, demonstrated that birds could count and identify objects, reinforcing the idea that cognitive abilities in birds warrant serious consideration.
Karten’s work laid the foundation for today’s scientific study of these remarkable birds. Today, Bastienne Zaremba and her lab members continue to investigate the conservation and divergence of neural circuitry between species. Zaremba was particularly surprised by the flexibility shown in how different animals evolved similar circuitry. He reported that, “How we arrive at the same circuitry ended up being a lot more flexible than I would have thought.”
Insights from Recent Studies on Neural Evolution
Fernando García-Moreno, a prominent researcher in this field, has contributed significantly to understanding how different vertebrate species developed their respective neural architectures. He argued that ancient Egyptians and South Americans both independently created pyramids. These lasting building types are a stunning testament to how various civilizations arrived at similar solutions to grand problems independently.
García-Moreno looked at how neurons matured in different areas. Regardless of their embryonic origin, these neurons develop to the same types within the adult bird pallium, providing clues into their evolutionary history. He concludes, “They were both right; they were both wrong.” This declaration illustrates the often convoluted theories about vertebrate pallium evolution.
García-Moreno’s team created what has been described as “the most comprehensive atlas of the bird pallium” utilizing RNA sequencing techniques. This atlas provides important information about how different species have evolved their neurological architectures. Along the way, it illuminates their unique approaches to flourishing in urban, suburban, and rural settings.
The Structure and Function of Bird Pallium and Mammalian Neocortex
In mammals, the neocortex is mostly organized into six different horizontal layers of neurons. These layers provide the basis for higher-order processing of sensory information and the coordination of appropriate behavioral responses. By contrast, the layered organization is missing from the bird pallium. As García-Moreno puts it, it’s made of “irregularly shaped clusters of neurons devoid of boundaries or features.”
Zaremba’s findings demonstrated that fully developed circuits in birds are strikingly comparable from one species to another. Yet, even though very similar in function, their construction is quite different from that of mammals. This divergence seems to indicate that birds and mammals have evolved distinct neural solutions to analogous, but functionally equivocal challenges presented by their environments.
Maria Tosches’ work went a long way towards demonstrating the limitations on how smart a brain can be built within vertebrates. She has artfully captured the ways that birds have evolved their forms to suit the pressures in their habitats. Onur Güntürkün illuminated the remarkable productivity of avian brains. He noted that “A bird with a 10-gram brain is performing essentially the same way in the end as a chimp with a 400-gram brain.”
These results together highlight an important difference in the ways that intelligence may manifest across species. Moreover, intelligence can develop on its own—intelligent creatures need not be closely related. This doesn’t imply that all adaptive strategies lead to identical cognitive outcomes, despite arising from entirely independent neural architectures.
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