Stanford researchers report the important finding that forebrain and hindbrain cells may originate from two different progenitor cells. Jokhai et al. finish with the implication:
the brain is a composite organ emanating from two lineage-restricted progenitors
The press release is more sensational: the human brain is "two separate organs" (title) or "two distinct organs."
The brain science seems solid. The brain is, indeed, a composite of multiple parts. The press release, however, is oversimplifying matters a bit.
There is historical precedence in neuroscience for theorizing about the existence of multiple brains. Paul MacLean's triune brain proposed three separate brain systems: reptilian (basal ganglia), paleomammalian (limbic system), and neomammalian (neocortex). Julian Jaynes bicameral mind proposed that the right and left hemispheres of the brain operated in a semi-independent manner. Changes in the experience of this arrangement were important for the emergence of modern consciousness. Both theories invoke evolutionary changes and consciousness. Both theories were popular several decades ago, but now are largely discredited.
What's fascinating to me is how this notion of the brain being composed of multiple brains attracts our attention. It resonates with people. It appeals to intuitions and seems plausible. Why is this so?
Lack of cognitive access to the inner workings of our mind is one plausible explanation.
There may also be a logical problem related to the fallacy of division, in which parts are mistakenly understood as having the same properties as the whole. If I pick a pepperoni off my pizza, I wouldn't call this part a "pizza." If I look at the tire on my car, I wouldn't call this component a car, or say that my car is based on four miniature cars. For these physical examples, the whole pizza or whole car is easily understood as being different from the constituent parts. That's obvious. But when we start thinking about psychology, brain functions, or consciousness, it suddenly becomes a plausible intuition to say that the part (a mini-brain) must have the same properties as the whole brain.
For consciousness research, I'm generally skeptical of efforts to decompose consciousness into parts and pieces. While there may be a strong intuitive appeal, this reductionism is misguided. Instead, we should look at the massive interconnections in the brain for inspiration. That's where the real explanation of consciousness lies.
Instead of two brains, triune brains, or bicameral minds, focus instead on the brain as a "composite organ."