The human brain wasn't exactly simple to begin with. Now, scientists have found evidence that its origin story may be even stranger than we thought.

New research from Stanford Medicine suggests the front and back portions of our brains begin from two entirely different groups of cells. In other words, we may have been walking around with two ancient neural systems packaged into one this whole time.

Scientists Found Two Starting Points

For decades, researchers generally worked from the idea that the brain began with one population of early progenitor cells. Eventually, those cells branch out to form the different regions of the brain.

But, researchers behind a new Nature Neuroscience study found something different. While studying early development in mouse embryos, the team identified two separate populations of progenitor cells appearing at the same time. One was destined to produce the forebrain and midbrain. The other was headed for the hindbrain.

Rather than beginning together and splitting somewhere down the road, these two developmental paths appear to be separate very early on.

The Two Parts Have Very Different Jobs

By adulthood, our brains have three major regions: the forebrain, midbrain, and hindbrain.

The forebrain is involved in the abilities we tend to associate with being human, like:

• Language

• Consciousness

• Abstract thinking

The hindbrain handles some less glamorous, but important, business. It helps control:

• Breathing

• Heart rate

• Sleep

• Hunger

• Swallowing

• Movements of the face and tongue

So, one ancient system helps us ponder the meaning of life. The other makes sure we continue breathing while doing so. Both seem worth keeping.

This Split May Be Incredibly Old

Here's where the story gets even stranger. The researchers looked at hundreds of millions of years of evolution and found evidence that this dual-system arrangement is ancient. The same basic pattern appears in animals, including chickens, zebrafish, and acorn worms.

The researchers believe the two progenitor systems may have remained distinct for roughly 550 million years. Even jellyfish, which split from our evolutionary branch hundreds of millions of years ago, have two nervous systems located at opposite ends of their bodies.

That led researchers to suggest that evolution may have taken two existing neural systems and brought them together in the same place.

The Discovery Could Help Scientists Grow Brain Cells

This isn't simply an interesting new way to think about what's happening inside our heads. The discovery may solve a problem scientists have struggled with for years. Researchers have had difficulty growing certain human hindbrain neurons in the laboratory. If the new findings are correct, they may have been starting with the wrong type of progenitor cell.

Using what they learned about the brain's separate developmental paths, the Stanford team was able to turn human pluripotent stem cells into functional hindbrain motor neurons.

Those cells could give researchers a better way to study diseases affecting the brain stem, including amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy.

Do We Really Have Two Brains?

Not exactly. We don't have two independent brains tucked inside our skulls, each fighting over what we're having for lunch. This research is about how different regions of the brain develop and where they originate.

As adults, those regions are physically connected and work together as the brain we've always known. But, their beginnings may be more separate than scientists realized. And after centuries of calling the brain a single organ, finding out that its earliest building blocks may have arrived on two different tracks is quite the anatomical plot twist.

At least now we have something else to blame when we can't decide what we want for dinner.

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