Human Brain Size Explanation. Chance Evolution Of 3 Mutations:
So the quest to know ourselves has been a long one.
Whether it’s the different projects directed at AI, or tracing all the brain’s connections,
Something about humanity is always searching for a type of mirror.
-Especially when that research proves we are not really 99% the “same” as a chimpanzee, or even 50% banana.
One of the biggest puzzles is how/why we all have such big Brains compared to other animals,
And in a strange X-Men-level twist of accidents, science just found out a big piece…
You Are A Mutant:
Another thing we do is to look for meaning in all the events of a story.
But this particular time, researchers in California and Holland found the answer to that search,
So before we rewind 14 Million years, 1 Clue.
The Human Genome Project wasn’t just “wrong”, it was Incomplete.
And that mistake was key to finding out why humans have a brain 3x the size of our closest cousin, the chimpanzee.
A Tiny Accident, And Then Another, And Then Another…:
So back 14 million years ago, when we split off from other great apes,
UCSC & U.Amsterdam researchers found that we picked up something accidental that no primate ever got.
An extra little wrinkle on chromosome 1 of our DNA, called a Notch Gene.
They checked all the other primates; none of them have it.
And by some miracle, they actually had the DNA from those ancient ancestors to check, too.
If Once Is Good, Isn’t 3 Times The Charm?:
But it didn’t just happen once.
This gene first popped up in an ape-ancestor all that time ago,
But it didn’t work.
It turned out to just be something called a “pseudogene”.
In the 15,000,000+ changes we’ve had in our DNA since chimpanzees,
11 million years after that first magic mistake, we got that gene copied 3 More Times.
And that’s when all of a sudden it Really started working.
So What Does It Do?:
Unlike anything else, those 3 NOTCH2NL genes make us do 3 things.
1) Delay final task-specialization changes of all starter brain-cells
2) Grow TONS more starter brain-cells that can become anything
3) Generate most of these cells in the very smartest part of our brain, the Neocortex
So one of the paradoxical things that happens, is that if a brain grows faster,
It reaches its final-mature-size faster, too.
And every cell that could do any job gets selected and specialized much earlier.
After that, all the ones deemed “extra” by the its own chemistry get trimmed-back over time.
So if you wanted to hack that process to make a truly super-brain what would you do?
NOTCH2NL Is Like Rocket-Fuel For The Size Of The Human Brain:
Well the 3 copies of that gene work-around that limit by doing the opposite.
They delay the final graduation-date,
And make Tons of cells that turn into trillions of rounds of ammunition for brain-awesomeness,
So that when they do start turning into their final form,
The brain has that much more “fuel” stockpiled-up, to get bigger,
And they tested this, too.
Researchers both added and subtracted these extra genes from test-samples and test-animals.
And in both cases, brain-development either shrank or accelerated accordingly.
All Discovered Largely From A Mistake:
A lot of this was possible because we’ve had 37 really-incomplete versions of the Human Genome so far.
The guys at UCSC didn’t even know that these 3 super-mutations were even on our DNA until Very recently.
That new update, Version 38, showed them all where these magical codes were.
So not only do we have a lot more to learn especially by using modern gene-editing techniques like CRISPR,
It turns out we are certainly a Lot different than even Chimpanzees.
15 Million+ changes different.
Including 3 tiny but Very important ones that explain the very large size of the human brain, the neocortex, and the beginning of its amazing potential!
Photo Credits: “drak glow”, by Sebastian Laube
• Source: UCSC
• Source Study: Cell – Human-Specific NOTCH2NL Genes Affect Notch Signaling and Cortical Neurogenesis