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

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

The discovery could help explain why scientists have struggled for decades to grow certain types of brain cells in the laboratory—and it opens new avenues for studying devastating diseases that affect the brain stem, such as spinal muscular atrophy (also known as SMA) and amyotrophic lateral sclerosis (also known as ALS or Lou Gehrig's disease).

"We've shown for the first time that the front of the brain arises from a totally different progenitor cell than the back of the brain," said Kyle Loh, Ph.D., associate professor of developmental biology. "Our discovery means that we can now grow neurons from the back of the brain, the hindbrain, in a Petri dish and study their functions."