For thousands of years, we've thought of the brain as a single organ. But new research suggests it may be more accurate to think of it as two separate systems that evolved independently before eventually working together as one. The finding challenges a long-held assumption about one of the most studied parts of the human body. 

Researchers found that the front and back portions of the brain appear to develop from different groups of cells very early in embryonic development. The hindbrain handles many of the functions we rarely think about, such as breathing, heart rate, and sleep. Meanwhile, the forebrain and midbrain are responsible for higher-level tasks including language, reasoning, consciousness, and abstract thought. 

The discovery may help explain why scientists have struggled to study and grow certain types of brain cells in the laboratory. It also sheds light on how the nervous system evolved over hundreds of millions of years. Researchers noted that similar dual-system patterns can be seen in animals as distant from humans as jellyfish, suggesting these separate systems have very deep evolutionary roots. 

Beyond rewriting biology textbooks, the findings could have practical benefits. A better understanding of how these two brain systems develop may eventually lead to new insights into conditions that affect the brainstem and nervous system, including diseases such as ALS and spinal muscular atrophy. Sometimes the biggest discoveries come from realizing that something we thought was one thing may actually be two.