The notion that a person’s IQ may be inferred from their head size is centuries old. As one’s brain size increases, one may assume that one’s capacity for processing and storing information also increases. Would you say that’s right?
A look at how the brains of various animals compare reveals that things are more complex. To put it simply, the sperm whale possesses the biggest brain of any living mammal. However, the marine mammal’s brain is just as massive as the rest of its body. Perhaps the ratio of brain to body weight is more important. As thus, the shrew would be the vertebrate with the greatest brain. Many previous studies have used a similar approach to establish relationships between the many different dimensions of the body and the many different characteristics of the brain. Humans, however, did not place top in any of these neurocharts, which was a major surprise.
The intelligence and adaptability of a species of animal cannot be inferred from its members’ (relative) brain sizes. The fundamental reason for this is because nerve cells vary in size and density between animal species. We have denser and more compact neural networks than many other animals, for example.
Could there be a correlation between brain size and behavior amongst different species? An old story concerning the burial of the German philosopher Friedrich Schiller demonstrates the plausibility of this idea. Goethe had already requested that Schiller be buried close to him in the Weimar Princely Crypt. However, the latter had passed away at a young age, and his burial location in the “cash vault” remained a mystery. After comparing other skulls to Schiller’s death mask and coming up empty-handed, the biggest skull was selected to be interred beside Goethe. The lofty soul, it is presumed, need extensive solitude in which to reflect.
A counterargument may be made that the smart large skull’s central argument is not completely off base. Research on the correlation between head size and intelligence began in the early 20th century. Although this studies generally pointed to a favorable correlation, first measurements were notoriously sloppy. The precise measurement of brain volume in live persons became possible with the advent of imaging techniques like magnetic resonance imaging (MRI) in the 1970s. Researchers look at absolute volume instead of body size when doing intraspecific comparisons. Such approaches in research have shown the importance of brain size in describing individual variations in IQ.
One study found that for every four-point gap in IQ between two persons, one point may be linked to differences in brain size. Indeed, the impact of such a change would be very remarkable. The subsequent publication of a plethora of study articles on the topic has mostly confirmed two findings: Brain size does correlate favorably with cognitive ability. However, this only accounts for around a one-in-twenty IQ point variation across individuals, so it’s hardly a convincing explanation.
In other words, there are numerous factors than brain size that contribute to our cognitive ability, thus we shouldn’t use brain size as a proxy for intelligence. The connectivity of neurons and the level of communication across brain regions are more important for intelligence than brain volume per se. The better the brain’s neural pathways, the more efficiently the various parts of the brain can communicate and collaborate.