The shape of the brain has evolved over thousands of years. It has become the way it is through random events that have changed its shape. These events, over time, have meant that we have become able to problem solve, communicate, plan ahead, modify our behaviour. If the brain was a different shape then we might function and behave differently.
The human brain is a very different shape compared to other animals. One thing that neuroscientists have noticed is that the smarter an animal is, the larger its brain compared to its body, and the more ‘wrinkled’ it is. Us humans have a large brain which is so convoluted that it looks like a walnut.
The theory is that, because the surface of the brain is really important, when the brain evolved to get bigger, it started to fold up to maximise this surface area, which is why our brain is the shape it is and not smooth like most other animal brains.