Yeah, while on that post i kept thinking wtf are you on about Elon, am sure i've read bigger brains could even result in less fluid intelligence. Excerpt with a nod to yours:
January 1, 2016
Does Brain Size Matter?
Turns out some species are better endowed than we are in key cognitive regions
By Christof Koch
[...]
...on average, a bigger brain is associated with somewhat higher intelligence. Whether a big brain causes high intelligence or, more likely, whether both are caused by other factors remains unknown.
Recent experiments take into account the particular connections among neurons in certain regions of an individual’s brain, much like a neural fingerprint. They do better at predicting fluid intelligence (the capacity to solve problems in novel situations, to find and match patterns, to reason independently of specific domains of knowledge), explaining about 25 percent of the variance in this measure from one person to the next.
Our ignorance when it comes to how intelligence arises from the brain is accentuated by several further observations. As alluded to earlier, the adult male’s brain is 150 grams heavier than the female’s organ. In the neocortex, the part of the forebrain responsible for perception, memory, language and reasoning, this disparity translates to 23 billion neurons for men versus 19 billion for women. As no difference exists in the average IQ between the two genders, why is there a difference in the basic number of switching elements?
It is also well established that the cranial capacity of Homo neanderthalensis, the proverbial caveman, was 150 to 200 cm3 bigger than that of modern humans. Yet despite their larger brain, Neandertals became extinct between 35,000 and 40,000 years ago, when Homo sapiens shared their European environment. What’s the point of having big brains if your small-brained cousins outcompete you?