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

> Stanford Medicine reveals human brain splits into two ancient nervous systems that evolved independently for hundreds of millions of years.
- Title: Human brain is two separate organs, Stanford Medicine-led…
- Summary: Stanford Medicine reveals human brain splits into two ancient nervous systems that evolved independently for hundreds of millions of years. The human brain…
- Keywords: stanford medicine, human brain, neural systems, hindbrain, forebrain, spinal muscular atrophy, amyotrophic lateral sclerosis, stem cells, embryonic development, gastrulation, chromatin, oxt2 gene
- Source: News Center — https://med.stanford.edu/news/all-news/2026/09/two-separate-brains.html
- Author: Krista Conger
- Published: 2026-09-18T00:00:00+00:00
- Read time: 2 min
- Topics: stanford medicine, human brain, neural systems, hindbrain, forebrain, spinal muscular atrophy, amyotrophic lateral sclerosis, stem cells, embryonic development, gastrulation, chromatin, oxt2 gene
## Brain's hidden split
Scientists thought the brain was one organ, but new research shows it's two distinct systems that evolved separately over hundreds of millions of years.

> 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
## Two brain systems
The human brain has two ancient nervous systems: one that controls basic functions like breathing and heartbeat, and another that enables human traits like poetry and math.
## Why it matters
This discovery explains why scientists have struggled to grow certain brain cells in labs and opens new ways to study diseases like spinal muscular atrophy and ALS.
## The breakthrough
Researchers found two brain progenitor cells that never overlap: one becomes the front brain, the other the back brain, with completely different genetic patterns.

> Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells which our study shows is not possible
## Lab growth success
Scientists first grew functional hindbrain neurons from human stem cells, which can now be studied for diseases affecting the brain stem.
## Evolutionary link
The same two-brain pattern exists in chickens, zebrafish, and acorn worms, showing this split evolved over 550 million years ago.
## Disease implications
This research helps understand spinal muscular atrophy and ALS, which affect brain stem neurons and cause swallowing and breathing problems.
## Obesity connection
The hindbrain regulates hunger, which explains how weight-loss drugs like semaglutide work by targeting these circuits.
## Key researchers
Kyle Loh, PhD, lead researcher, says the brain's split explains why scientists have struggled to grow hindbrain neurons in labs for decades.
## Future work
Researchers aim to study spinal cord development and how spinal muscular atrophy and ALS damage hindbrain neurons.
## Evolutionary insight
The brain evolved from two separate neural systems that merged over time, creating a more complex but less efficient structure.
## Patient impact
This discovery could lead to new treatments for spinal muscular atrophy and ALS by growing brain stem neurons in labs.
## Long-term vision
Researchers hope to unlock more mysteries of the brain, including how neural systems develop and interact.
## Funding sources
The study was supported by NIH, NSF, Stanford, and foundations focused on spinal muscular atrophy research.
## Key findings
The hindbrain and forebrain develop from separate cells with no overlap, explaining why scientists couldn't grow hindbrain neurons before.
## Historical context
This discovery overturns the long-held belief that the brain develops from a single progenitor cell that creates all brain parts.
## Key takeaway

The human brain consists of two distinct organs that evolved separately, with one regulating basic functions and the other enabling human traits.