To know why your brain in wrinkly, just look at your mum’s hips.
We all know that the brain has wrinkles. Why?
The system of inward (sucli) and outward (gyri) folds allow a larger cortex to be fitted into a constrained cranium. And the size of the cranium is limited by what size head can fit through the pelvic bone during birth.
In the image above, the upper section shows representations of brain activity on realistic models of the brain. But the areas deep in the sulci cannot be seen clearly. Therefore the lower images show the same activity maps on models of the same brains, as if they had been inflated. This not only shows the deeper areas that can be hidden, but also shows how much bigger the brain would need to be if the cortex wasn’t folded.
Edit: Want to read more on folding? Try this: