Human brain has a split origin!

For centuries, scientists have thought of the brain as a single, unified organ. Why only scientists, everybody thought that the brain is a single organ all these days! But new research reveals that what we call the brain is two distinct organs that evolved independently over hundreds of millions of years.
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).

Some time back I painted this picture:  Dark & Light Shades of Human Nature

Then I didn't know that the brain is actually two neural systems that came together to look like one! 

Source: https://www.kkartfromscience.com/fromscience.html#

Scientists have shown for the first time that the front of the brain arises from a totally different progenitor cell than the back of the brain. This discovery means that we can now grow neurons from the back of the brain, the hindbrain, in a Petri dish and study their functions.

The adult brain has three main regions: the forebrain, midbrain and hindbrain. The forebrain handles higher-level thinking—language, consciousness and abstract reasoning. In contrast, the hindbrain, located at the back of the skull and often called the brain stem, controls essential, automatic functions that keep us alive: breathing, sleeping and regulating our heartbeat and hunger urges. Hindbrain neurons also control the muscles of the face, tongue and throat, which affect speech and swallowing.

Despite the critical importance of the hindbrain, scientists have struggled for decades to generate human hindbrain neurons in the laboratory. This gap has hampered research into devastating diseases affecting the brain stem, including spinal muscular atrophy and amyotrophic lateral sclerosis.

SMA is a leading genetic cause of death in children under 1 year of age. ALS, which is often diagnosed between the ages of 40–70, affects both the forebrain and the hindbrain. In both disorders, certain hindbrain neurons gradually cease to function, and the patient loses the ability to swallow, which can cause pneumonia when food or liquid is inhaled into the lungs. Eventually, patients lose the ability to breathe.

The researchers' breakthrough came from studying the earliest moments of embryonic development, during a stage called gastrulation, when the body first takes shape.

Researchers discovered that the hindbrain follows a separate developmental path, running in parallel to—rather than branching off from—the pathway that creates the forebrain and midbrain.
The researchers learned this by examining developing mouse embryos. They identified two different brain progenitor cells. One, which expresses a gene called Otx2, is destined to become the forebrain and midbrain. The other, which expresses a gene called Gbx2, is committed to forming the hindbrain. They showed that these two cell populations never overlap; they are mutually exclusive from the earliest stages of development.

The team then examined the DNA packaging, or chromatin, in these cells. Chromatin is a way cells determine which genes can be easily accessed and which are bundled away out of reach. What they found was striking: The anterior neural ectoderm (future forebrain and midbrain) and posterior neural ectoderm (future hindbrain) have fundamentally different chromatin configurations. These differences essentially locked each progenitor cell into its respective fate, like travellers on parallel tracks that never cross.

Previous attempts to make hindbrain neurons likely tried to coax forebrain and midbrain progenitors into hindbrain cells, which this study shows is not possible.
This revelation explained decades of frustration in the field—scientists had been trying to turn one type of progenitor cell into another that it is fundamentally incapable of becoming.

Armed with this knowledge, the researchers for the first time successfully coaxed human pluripotent stem cells (a kind of cell that can create any cell in the human body) to become functional hindbrain motor neurons in the laboratory. These lab-grown neurons displayed all the hallmarks of authentic hindbrain cells: They exhibited waves of electrical activity called action potentials and made proteins that identify the segments of the hindbrain that control facial and swallowing muscles.

Finally, the researchers looked back over 550 million years of evolutionary time. They found the same two-origin brain pattern in chickens, zebrafish and, remarkably, acorn worms, tiny creatures living on the ocean floor that share a distant common ancestor with humans. Jellyfish, which diverged from humans about 600–700 million years ago, have two nervous systems at different ends of their bodies.

This research suggests that evolution took two existing neural systems and pushed them together spatially.
This is really interesting as the word 'brain' implies a contiguous organ that likely has a singular origin. But even 500 million years ago, there were these separate neural systems, which now almost operate as one, which is very cool.

Scientific research never ceases to thrill me. What a day to find out  that the most exciting thing happens in the box above your body!

And why did I paint the picture above just the way it should be done? Things are getting more electrifying now. WOW!

Two parallel neural ectoderm progenitors contribute to the developing brain, Nature Neuroscience (2026). DOI: 10.1038/s41593-026-02433-7