Suzana Herculano-Houzel in Nautilus:
We have long deemed ourselves to be at the pinnacle of cognitive abilities among animals. But that is different from being at the pinnacle of evolution in a number of very important ways. As Mark Twain pointed out in 1903, to presume that evolution has been a long path leading to humans as its crowning achievement is just as preposterous as presuming that the whole purpose of building the Eiffel Tower was to put that final coat of paint on its tip. Moreover, evolution is not synonymous with progress, but simply change over time. And humans aren’t even the youngest, most recently evolved species. For example, more than 500 new species of cichlid fish in Lake Victoria, the youngest of the great African lakes, have appeared since it filled with water some 14,500 years ago. Still, there is something unique about our brain that makes it cognitively able to ponder even its own constitution and the reasons for its own presumption that it reigns over all other brains. If we are the ones putting other animals under the microscope, and not the other way around, then the human brain must have something that no other brain has.
Sheer mass would be the obvious candidate: If the brain is what generates conscious cognition, having more brain should only mean more cognitive abilities. But here the elephant in the room is, well, the elephant—a species that is larger-brained than humans, but not equipped with behaviors as complex and flexible as ours. Besides, equating larger brain size with greater cognitive capabilities presupposes that all brains are made the same way, starting with a similar relationship between brain size and number of neurons. But my colleagues and I already knew that all brains were not made the same. Primates have a clear advantage over other mammals, which lies in an evolutionary turn of events that resulted in the economical way in which neurons are added to their brain, without the massive increases in average cell size seen in other mammals.
We also knew how many neurons different brains were made of, and so we could rephrase “more brain” and test it.
More here.
