It's common to hear people say that the size of your brain has nothing to do with your level of intelligence. (Not me, though, because I have a big head and I'll take any perceived genetic advantage I can get.)
And certainly, in individual cases, the idea that the size of your brain has nothing to do with your level of intelligence is true... but decades of evidence shows that people with bigger brains do tend to perform better at tasks related to intelligence.
As the researchers say, "This moderate structure-function relationship can be observed for the whole brain, its lobar volumes, and even within specific brain areas predominantly located in parieto-frontal regions."
Or in non researcher-speak, the bigger your brain, the more neurons you probably have... so the more "computational power" you have to solve problems and reason logically.
So yes: On average, people with bigger heads tend to be more intelligent. (Great news for lollipop people.)
Still, size alone doesn't tell the whole story. Research also shows that intelligence is not a function of how hard the brain works... but of how efficiently it works. (That premise is known as the neural efficiency hypothesis of intelligence.)
Greater intelligence is based on relatively efficient, not relatively high, information processing. Larger brains have low neuron density and low neuron orientation dispersion. That means larger brains do have more neurons, but more importantly they have fewer connections between those neurons and therefore process information more efficiently.
As one of the authors of the study says,
"The brains of intelligent people demonstrated less neuronal activity during an IQ test than the brains of less intelligent individuals.
Intelligent brains possess lean, yet efficient neuronal connections. Thus, they boast high mental performance at low neuronal activity."
What all that means is that people with high IQs tend -- tend -- to have larger brains. They also tend to have fewer connections between neurons, which means they can more easily differentiate signal from noise and use less energy and operate more efficiently. If you think of a brain as a network, higher intelligence is associated with a clean, well-organized set of connections -- all of which means better processing speed.
Which leads to higher intelligence.
Does that mean people with large heads are automatically smarter? No. But it does mean they might have the potential to be smarter.
And, of course, so do people with small heads.
As with many things related to size, what really matters is what you do with what you have. Like adopting a growth mindset. Or exercising on a regular basis. (Seriously; that works.) Or even just looking at the color red for a few seconds. (Yep, that works too.)
And of course there are plenty of other indications of intelligence; even something as simple as craving time alone suggests you might be smarter than average.
Having a bigger or a smaller brain isn't something you control. But what you do with what you have?
That means everything.