Human brain is two separate organs, Stanford Medicine-led research finds

For centuries, scientists have thought of the brain as a single, unified organ. But new research led by Stanford Medicine reveals that what we call the brain is two distinct organs that evolved independently over hundreds of millions of years.

The discovery overturns a prevailing model of brain development. For decades researchers have subscribed to the theory that there is a single progenitor cell early in development that gives rise to the entire brain. This model suggested all parts of the brain shared a common developmental origin.

The new research finding shows that the human brain consists of two ancient nervous systems cleverly packaged together — a more primitive part that regulates our hearts’ beating, our breathing and other functions, and another that makes us distinctly human, capable of poetry, mathematics and wondering about our own origins.