TLDR: Evolution of mammalian brains post-mass extinction wasn’t linear; trade-offs in energy and ecological changes shaped their development.
This article is a summary of a You Tube video “How a Mass Extinction Changed Our Brains” by PBS Eons
Key Takeaways:
- Mammalian Brain Evolution Complex: Contrary to popular belief, the evolution of large, complex mammalian brains wasn’t a straightforward or inevitable process.
- Encephalization and Intelligence: Encephalization, the ratio of brain to body size, broadly correlates with intelligence in vertebrates, with modern mammals, especially humans, apes, whales, and dolphins, being highly encephalized.
- Post-Extinction Brain Development: After the K-Pg extinction (which wiped out non-avian dinosaurs), mammalian brains shrank relative to their bodies as mammals grew in size more rapidly than their brains.
- Energy Trade-offs in Evolution: A larger brain is more energetically costly. Post-K-Pg, mammals prioritized body size over brain size due to the energy trade-offs.
- Paleocene Mammals’ Brain and Body Growth: During the Paleocene epoch, following the K-Pg extinction, mammalian body sizes grew faster than brain sizes, resulting in lower encephalization.
- Eocene Epoch and Encephalization: In the Eocene epoch, mammalian brains began to grow proportionally with the body, leading to increased encephalization, particularly in early forms of current mammalian groups like horses, whales, dogs, bats, and primates.
- Changes in Brain Structure: Alongside increased encephalization, there were significant changes in brain structure, with reduced olfactory regions and expanded areas for vision, eye movement, balance, and higher-order thinking.
- Adaptation to Competitive Ecosystems: The shift towards larger brains in mammals was likely driven by the fully recovered and competitive ecosystems post-Eocene, where cognitive abilities became advantageous.
- No Linear Evolution Towards Intelligence: The evolutionary path towards larger, more complex brains wasn’t linear, highlighting the role of ecological contexts and trade-offs in evolution.
- Evolution Driven by Context and Trade-offs: Evolutionary advancements, like larger brains, are contingent on ecological circumstances and the need to balance various survival factors.
