The human brain may have originated from two ancient nervous systems that evolved separately before eventually becoming integrated into a single organ. New research examining embryonic development suggests that the front and back regions of the brain arise from distinct types of progenitor cells, challenging the idea that the entire brain shares one developmental origin.
Two Different Origins Within the Developing Brain
Researchers studying early mouse embryos found that the brain develops from two types of progenitor cells. These proliferative cells have a limited capacity for self-renewal and ultimately produce neurons belonging to different regions of the brain.
One type expresses a gene called OTX2 and develops into neurons in the front portion of the brain, including the forebrain and midbrain.
The second type expresses GBX2 and produces neurons in the hindbrain, located toward the back of the brain.
“Our research suggests that evolution took two existing neural systems and pushed them together spatially,” said Kyle Loh of Stanford University. “Having the brain as one organ would probably be more efficient, but we rely on this primordial way to make the brain as two separate pieces.”
Human Cells Reveal the Same Developmental Split
Experiments involving human cells grown in laboratory conditions showed the same basic pattern. Hindbrain neurons developed from different progenitor cells than neurons destined to form the forebrain and midbrain.
“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,” Loh said.
The discovery may help explain why scientists have historically found it difficult to grow human hindbrain tissue in the laboratory.
“It was actually a summer student’s failed experiment that got us into this,” Loh said.
Researchers had generally attempted to produce hindbrain neurons using progenitor cells that were naturally destined to become forebrain and midbrain neurons. According to Loh, those attempts failed because the experiments were starting with the wrong type of progenitor cell.
Using the newly identified developmental pathway, the research team was able to grow functional human hindbrain motor neurons in a laboratory for the first time by beginning with the appropriate progenitor cells.
Potential Implications for ALS and Other Research
The hindbrain regulates several fundamental processes required for survival, including breathing, sleeping, eating and heartbeat. The forebrain, meanwhile, is closely associated with higher-level cognitive functions.
A better ability to produce human hindbrain neurons could provide researchers with new ways to investigate neurological conditions such as amyotrophic lateral sclerosis, or ALS, and spinal muscular atrophy. Both disorders can cause difficulties with speech and swallowing because they affect motor neurons involved in these functions.
The findings could also contribute to research into GLP-1 medications such as Ozempic and Wegovy. Scientists have found that these drugs can suppress appetite in mice through effects involving the hindbrain.
With researchers now better able to grow human hindbrain neurons under laboratory conditions, Loh said the technique could support studies of ALS and spinal muscular atrophy while helping scientists examine more precisely how GLP-1 drugs work in humans.
Evolutionary Split May Be More Than 550 Million Years Old
The researchers also examined early-stage embryos from chickens, zebrafish and acorn worms. Their nervous systems showed a similar developmental pattern, arising from two different types of progenitor cells.
The presence of the same basic system across widely separated species suggests that this dual-origin organization may have emerged in a shared ancestor at least 550 million years ago.
Jellyfish may offer another clue about how the arrangement evolved. Their lineage diverged from ours roughly 600 million to 700 million years ago, and jellyfish possess two separate nervous systems.
Researchers suggest that comparable neural systems may have eventually become joined in distant ancestors, potentially improving the efficiency of information processing.
“You get more efficient communication when things are closer together,” Loh said.
Separate Development May Have Supported Complex Thought
The brain’s two developmental pathways may also have influenced the evolution of sophisticated cognition.
With the hindbrain responsible for essential functions needed to keep an organism alive, the forebrain may have had greater evolutionary flexibility to change without disrupting those fundamental processes.
While the hindbrain handled basic survival functions, “evolution could play around with the forebrain, and make mistakes and give rise to all the fancy things like memory and creativity,” Loh said.
The findings suggest that the modern brain may be the evolutionary product of two ancient neural systems brought together into a single structure. Beyond offering a new perspective on brain evolution, the discovery could provide scientists with improved laboratory models for studying neurological disorders and understanding how drugs affect specific regions of the human nervous system.
William Faulkner is a contributor to Columbuspost.com, covering a broad range of topics including news, politics, business, technology, sports, entertainment, and lifestyle. He focuses on delivering clear, accurate reporting and useful information that helps readers stay informed about current events and developments. His work highlights stories that matter to local and wider communities, with an emphasis on relevance, clarity, and providing readers with a balanced understanding of the issues shaping everyday life.
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