A 9.5-day-old mouse embryo. The front of the brain is blue and the back of the brain is red, which extends into the spinal cordLoh Laboratory/Stanford Medicine Our brain may be a hybrid of two ancient nervous systems that were packaged together hundreds of millions of years ago. This is based on the finding that the front and back brain regions in people and several other species develop from two distinct cell types in embryos, instead of sharing the same developmental origin, as previously thought. “Our research suggests that evolution took two existing neural systems and pushed them together spatially,” says Kyle Loh at Stanford University. “Having the brain as one organ would probably be ...