Brain asymmetry describes the asymmetrical function and structure of the brain in many animals, including humans. There are significant advantages to having an asymmetrical brain, including the ability to handle more complex concepts. It is important to note that brain asymmetry is often simplified or exaggerated for the purpose of roughly describing the concept; speech, for example, is often described as a left brain function, but the right brain also plays a role.
Structurally, the two halves of the human brain are slightly different. These differences develop during gestation and are determined by genetics and the shape of the skull. Some structures are larger or smaller on one half of the brain than the other, and the density and composition of nerve cells can also vary. Specialized structures reflect evolutionary changes and play an important role in human cognition, although the entire mass of the brain is not utilized with complete efficiency; there are vestigial structures that appear underused or unused, for instance.
Functionally, the two halves of the brain tend to focus on different things, with specific areas processing particular types of cognitive tasks ranging from fine motor control to doing math. Injuries to the brain can cause impairments, although in young people, the brain may be able to remap itself, transferring the function to another location to make up for the damaged area. In older people where the brain's functions are firmly mapped out, brain damage can be devastating, as the patient may not be able to recover a given function.
Numerous studies on brain asymmetry provide evidence for how it develops. Neurologists can create detailed maps of brain structure and function with the assistance of medical imaging, as well as examination of human brains. This information is useful in the practice of medicine, so surgeons know which areas of the brain to exercise caution around. People can also identify the location of brain damage by evaluating symptoms, allowing them to quickly narrow down on the source of the problem.
In organisms with wholly symmetrical brains where tasks are split evenly across the two halves of the brain, multitasking is challenging. The organism will have a split focus, rather than being able to perform two tasks at once. Brain asymmetry allows for activities like typing, where someone can watch a screen or a piece of paper to evaluate the output, while moving the fingers across the keyboard. A variety of complex tasks from driving to successfully following a recipe rely on brain asymmetry.