At LiveScience, Olivia Farrari details an interesting fact: Smarter dogs have smaller brains:

The research, published Nov. 13 in the journal Biology Letters, suggests that while working dogs may have more complex abilities compared with other breeds, they’re organized into a more compact space in the brain. This differs from what’s seen in evolutionary history in wild mammals, where as brains get bigger relative to body size, cognitive skills tend to become more complex.

“In other groups [of species] relative brain size is indicative of higher cognitive abilities — here we see the opposite,” said Ana Balcarcel, lead author of the new study and an evolutionary biologist at the Montpellier Institute of Evolutionary Sciences in France.

“Smarter dogs have smaller brains, surprising study reveals,” November 14, 2024

From the study’s Abstract :

Function, body size, phylogenetic clade and cranial shape correlate with REV [Relative Endocranial Volume]. Toy dogs, functioning mainly as companions, have the largest endocranial volumes relative to their body size. Working dogs, bred to perform complex human-assistance skills and reportedly possessing higher cognitive abilities, have the smallest. Our results thus show that complex skills and cooperative behaviour—a hallmark of social cognition—do not predict larger REV in dogs.

Wait

The underlying assumption is that brain size is a physical representation of brain power but there is no specific reason to believe that that is true. Let’s take human brains as an example.

My co-author of The Immortal Mind (Worthy June 3, 2025), neurosurgeon Michael Egnor has cut human brains in half or removed large parts of them and helped people live easier lives as a result.

Let’s start with: The reason that a nematode worm, or for that matter, an elephant, is not as smart as a human is not simply a question of brain size. Part of the difference between humans and animals is not physical at all.

You may also wish to read: Some people think and speak with only half a brain. A new study sheds light on
how they do it.