For centuries, a common assumption has been that a larger brain equates to greater intelligence. If a human brain, at roughly 1400 grams, is ten times heavier than a baboon's 140-gram brain, it seems logical to conclude humans are ten times smarter. But this simplistic metric quickly falls apart when you consider the animal kingdom.
The Flawed Logic of Brain-to-Body Ratios
By that same logic, a blue whale with its colossal 7-kilogram brain would far outstrip human intellect. Clearly, raw brain weight is a poor indicator. Scientists then turned to the brain-to-body mass ratio for a clearer picture. Here, humans score a ratio of approximately 1:52. However, we are still outclassed by the blue whale's impressive 1:8.3 ratio. The plot thickens further when considering the moose, which scores 1:67. As there are no recorded moose Nobel laureates, it's evident this metric also fails to capture the full story of intelligence.
Evolutionary Trends and the Neanderthal Puzzle
Another approach is to track brain volume over evolutionary time. Early hominins like Australopithecus, from three million years ago, had an average cranial capacity of 450 cubic centimetres, only slightly larger than modern chimpanzees. This increased to about 600cc with Homo habilis two million years ago, and further to 850-1100cc with Homo erectus.
Modern Homo sapiens emerged during the Pleistocene epoch with a cranial capacity averaging 1473cc. Intriguingly, this has seen a slight decrease over the last 3,000 to 10,000 years, prompting the question of whether ancient humans were smarter. Complicating matters further, Neanderthals possessed brains that rivalled or even exceeded ours, with some specimens measuring up to 1740cc. While brain size offers a reasonable approximation, factors like skull thickness and ageing affect these measurements.
Neuron Density and the Problem of Defining Intelligence
The search for a clear metric leads to other factors, such as the density of neurons within the brain. This helps explain the remarkable problem-solving abilities and tool use observed in birds like crows and parrots, which pack a high number of neurons into a relatively small brain.
This entire field has historically been ripe for confirming biases, from ancient Greek philosophers to the thoroughly debunked 1994 book The Bell Curve, which falsely attempted to link race and intelligence. The fundamental challenge remains defining what we mean by 'intelligence' itself. Can an immensely subtle and multifaceted trait truly be reduced to a single number derived from physical measurements? That question, as experts note, is a rabbit hole for another day.
Ultimately, the science reveals a nuanced truth: while a sufficiently complex brain is necessary for higher intelligence, size alone is not the decisive factor. The architecture, connectivity, and density of neural networks play a far more critical role in the cognitive abilities that define species from clever corvids to modern humans.
