Brain Size And Intelligence Are Not Connected

The belief that a bigger brain size means greater intelligence has been deeply ingrained in the human psyche. We’ve long assumed that the most cognitively advanced (smart!) species must boast the largest craniums. And humans have proudly declared our reign as the kings of the animal kingdom. However, a groundbreaking study published in Science Advances has challenged this long-held notion. It sheds new light on the complex relationship between brain size and intelligence.

The study examined the brain-to-body size ratios of over 1,400 living and extinct mammalian species. Their findings reveal a surprising lack of consistency in how brain size has evolved over the past 150 million years.

brain size comparison chart — Brain size comparison chart — does it matter?
Source: “The Evolution of the Brain, the Human Nature of Cortical Circuits, and Intellectual Creativity,” by Javier DeFelipe, in Frontiers in Neuroanatomy, Vol. 5, Article No. 29. Published online May 16, 2011

Elephants, Dolphins, and Great Apes

Contrary to popular belief, researchers made an interesting discovery. They found that “big-brained” animals like humans, dolphins, and elephants attained this big-brainedness in vastly different ways. Elephants, for example, increased in both body and brain size as they evolved. However, dolphins generally decreased their body size while increasing their brain size. On the other hand, great apes exhibit a wide range of body sizes. They tended to increase both brain and body size together.

Humans

The study also revealed intriguing insights about our own evolutionary lineage. Ancestral hominins, which include modern humans, showed a relative decrease in body size. At the same time, they had an increase in brain size compared to their great ape counterparts. This implies that our cognitive abilities developed through a complex interplay of various evolutionary pressures. It was not simply a matter of brain size expansion.

The Impact of Cataclysmic Events on Brain-Body Scaling

The researchers noted significant changes in brain size after two major happenings in Earth’s history. These changes occurred after the mass extinction 66 million years ago. They also occurred after a climatic transition 23 to 33 million years ago. These cataclysmic events seem to have triggered dramatic shifts in brain-body scaling. Certain animal lineages have experienced these changes, such as rodents, bats, and the carnivores filling the niche left by the extinct dinosaurs.

The Highly Intelligent California Sea Lion

The California sea lion is extremely smart. Despite its exceptional cognitive abilities, though, the sea lion has a relatively low brain-to-body ratio. Natural selection favored larger bodies that were more advantageous for living in oceans. There was no selection on decreased brain size.

Rethinking the Relationship Between Brain Size and Intelligence

The findings challenge the deeply rooted belief that a larger brain automatically indicates greater intelligence. The study’s authors suggest a shift in focus toward neuroanatomical features of the brain. This shift is needed for a true understanding of the evolution of intelligence, rather than relying solely on brain size. They encourage future research to delve deeper into the complex cellular organization of neural connections. This area may hold the key to understanding the true basis of cognitive capacity.

The Curious Case of Albert Einstein

The study’s findings also shed light on the case of renowned genius Albert Einstein. His brain was found to be of average size. This challenges the simplistic notion that a larger brain automatically translates to higher intelligence. As the research suggests, the complexity of neural connections may be far more important. Their efficiency might determine cognitive abilities more than sheer brain volume.

Exploring the Nuances of Brain Size and Intelligence

Advanced imaging techniques have emerged, such as magnetic resonance imaging (MRI). These techniques have allowed researchers to delve deeper into the relationship between brain size and intelligence within the human population. While some studies have found a moderate correlation between brain volume and IQ scores, these findings are far from conclusive. They do not account for the full spectrum of human cognitive abilities.

It is important to recognize that IQ tests, while widely used, do not provide a comprehensive measure of intelligence. They primarily assess certain types of cognitive skills, such as problem-solving and logical reasoning. However, they often fail to capture other important aspects of intelligence, such as creativity, emotional intelligence, and practical problem-solving abilities.

Most neuroscientists now believe that the true determinant of a brain’s intelligence lies in the complexity of its cellular and molecular organization. The density and efficiency of neural connections, or synapses, play a key role. This view is supported by findings that intelligence is more strongly correlated with the volume of the frontal lobe and gray matter. These areas are rich in neural cell bodies and synapses. Intelligence is linked to these factors rather than sheer brain size.

Comparative studies examining the proteins found at synapses across different species have provided valuable insights. These studies show how the molecular composition of neural connections has evolved. This evolution has shaped cognitive abilities throughout history. This suggests that the intricate details of brain structure and function are crucial. They play a significant role in determining an organism’s intellectual prowess, rather than just brain size.