A major study has shown that the human brain is in fact two separate organs joined together. For centuries, science has treated the human brain as one unified organ that grows from a single pool of early cells. Researchers at Stanford Medicine have overturned that textbook definition. Published in the journal Nature Neuroscience, their study shows that what we call the brain is two ancient, independent nervous systems assembled side by side over evolutionary history. By analysing mouse embryos, the team found that the forebrain and midbrain, which govern reasoning, language and consciousness, develop from an entirely different set of progenitor cells than the hindbrain, which controls vital autonomic functions such as heartbeat, breathing and swallowing. This biological split explains why scientists have struggled for decades to grow specific types of brainstem cells in laboratories, because they were trying to force forebrain cells into hindbrain roles. Armed with this new blueprint, the Stanford team guided human stem cells into becoming fully functional hindbrain motor neurons in a petri dish. This advance supplies a critical experimental platform for studying devastating neurodegenerative disorders, such as amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy, in which the degeneration of these specific neurons takes from patients the ability to breathe and swallow. [Jokhai, R. T., Dundes, C. E., and Loh, K. M., et al. (2026). Two parallel neural ectoderm progenitors contribute to the developing brain. Nature Neuroscience. DOI: 10.1038/s41593-026-02433-7]

The scale of the Universe. Scientifically, the universe spans an enormous range of sizes: from the Planck length, about 1.6 x 10⁻³⁵ meters, which is the smallest scale where our current laws of physics may still apply, to the observable universe, about 9.2 x 10²⁶ meters across.