Of course, there's isn't a simple answer to that question.
While some brain features are more common in one sex than the other, and some are typically found in both, most people have a unique mix.
Research has found some key differences that could explain why we expect males and females to think and behave in characteristic ways.
But even if the physical brain doesn't change, how it works can.
Most Brains Are Both
A 2015 study at Tel Aviv University used an interesting and very thorough approach to compare the structure of male and female brains. Researchers looked at MRI scans of more than 1,400 people.
First, they measured the amount and location of gray matter (sometimes called "thinking matter") in 116 parts of the brain to find out which areas had the biggest sex differences. Next, the team scored these areas on each scan as either falling into the "female-end" zone, the "male-end" zone, or somewhere in the middle.
It turned out that maybe 6 in every 100 of the brains they studied were consistently a single sex. Many others had a patchwork quilt of masculine and feminine features that varied widely from person to person.
To check their findings, the team used similar methods to analyze more than 5,500 people's personality traits and behavior. While some activities were more common in women (including scrapbooking, chatting on the phone, and keeping in touch with mom) and others in men (such as golfing, playing video games, and gambling), 98% of those studied didn't fit a clear-cut gender profile.
Overall, the findings suggest that "human brains do not belong to one of two distinct categories."
'Brain Road Maps' Reveal Differences
While the MRI research mainly focused on brain structures, another scientist has been exploring the nerve pathways that link them, like a highway system for the brain's traffic.
We know that hormones influence brain development in the womb, yet before age 13, boys' and girls' mental circuitry appears similar. During puberty, hormones may again have a powerful effect and contribute to rewriting the teen brain.
"Our studies are finding significant differences in the brain circuitry of men and women, even when they're doing the same thing: It's like two people driving from Philadelphia to New York, who take different routes, but end up at the same place," says Ragini Verma, PhD, associate professor at the University of Pennsylvania in Philadelphia.
Her team has looked at nearly 2,000 healthy people, including kids, teens, and young adults who took various tests of their mental skills. Differences in their "brain road maps" (scientifically known as "the connectome") can explain why males outperform females on certain tests of mental skills, while females have the edge in others.
Who Is Better?
Women have more connections going left and right across the two halves of the brain. This could give them an advantage in pulling together information from different sources and drawing conclusions. The left half of the brain handles logical thinking, and the right is associated with intuition.
Men's brains have more connections from front to back, which may heighten their perception. They may be more attuned to what's going on around them so they can take action. Men have stronger connections between brain areas for motor and spatial skills. That means males tend to do a better job at tasks that need hand-eye coordination and understanding where objects are in space, such as throwing a ball or hammering a nail.
On average, male brains are about 10% larger than female brains. "However, bigger doesn't mean smarter," says Daniel Amen, MD, author of Unleash the Power of the Female Brain. He's studied more than 45,000 brain scans. "And no differences have been found in men and women's IQs, regardless of brain size."
MRIs showed the biggest gaps between the sexes were the larger amount of gray matter women had in their hippocampus, a structure that plays a role in memory, and the left caudate, which is thought to control our communication skills. Verma found that in female brains, there's more wiring in regions linked to memory and social cognition. So is it surprising that women tend to be better at understanding how other people are feeling and knowing the right way to respond in social situations?
Not only could recent findings change how scientists study the brain, but this research could also have important health benefits, like better treatments for disorders that affect one sex more than the other.
Patterns Aren't Rules
While these insights are intriguing, Verma emphasizes that they don't necessarily apply to everyone. "Our studies are comparing the performance of males and females, on average, on certain tasks," she says.
The Tel Aviv study supports the idea that sex differences in the brain may depend on the family and culture you grew up in and what's happened to you, too.
When your brain processes the same signals over and over, those networks will get stronger, like working out a muscle. So even if male and female brains start out similar, they may become different over time as boys and girls are treated differently with different expectations.
And brains can adapt. Like when someone loses their sight, they get better at hearing. They use the "seeing" part of their brain to process sound.
"Individuals of both sexes can have large variations in their abilities," Verma says. "For example, I have three math degrees but no sense of direction."