Good morning,

How has everything been going? I hope you’re doing well.

I’m in Utah this weekend enjoying some wonderful autumn weather. Later today, I’m driving in my Jeep down toward southern Utah / northern Arizona.

Here’s what I have for you today:

• One big thing. What do Komodo dragons, shape-shifting robots, and your own brain have in common? Each reveals how experience sculpts neural architecture over time.

• You have to check this out. A thinking framework for understanding medical research.

Ready to jump in? 🦘

1️⃣ ONE BIG THING

Your livewired brain.

I never thought I’d be impressed by kidneys.

But there I was, on one of my long podcast walks in my neighborhood, listening to Peter Attia talking to Ralph DeFronzo about insulin resistance. As a conversational aside, they described how kidneys work. I can still remember the street I was on when I heard this. It was a moment of awe. Kidney awe.

Nature faces many seemingly unsolvable dilemmas. Imagine it’s 200 million years ago, and you are designing the first mammals. Your new warm-blooded creatures will need to maintain precise water and salt balances if this whole invention is going to work. Secondly, you need to filter their warm blood of toxins on the regular because who knows what these mammals are going to eat or absorb through their lungs and skin. You need to design an organ that can do both.

But there is a bigger problem: You want your new design to work for millions of years, but how will you ever predict that your mammals living in 2025 might absorb microplastics or consume Ambien? How do you design a filtering organ when you can’t predict what needs to be filtered?

Like most answers shaped by evolution, the answer is stunningly simple: you don’t decide what to filter at all.

Instead, you filter everything and then put the things you know you need (like water and electrolytes) back into the blood in exactly the right amounts.

This is an elegant solution. A simple solution to a complex problem.

Evolution itself is an elegant solution—one that, by design, creates other elegant solutions.

Hardware and software.

Your smartphone is another elegant solution. A big evolutionary step in its design was the removal of the fixed keyboard (the BlackBerry design became the iPhone design). Leaving the entire front of the phone available to serve as a keyboard, video screen, or chessboard allows the phone to adapt to many uses, including tons of uses we cannot imagine today (but probably still involving cat videos).

The hardware in your phone is fixed: a chip, circuits, battery, screen, case, etc. It is the adaptability of the software that makes the phone so elegant. Every user has different apps and a home screen layout set just how they want it. As times change, quick software updates enable new uses.

As technology advances and new uses for smartphones emerge, however, the hardware also must change. For example, you might need a faster processor and a better battery to run the latest apps.

If you wanted to design the most elegant smartphone, both the hardware and the software would adapt over time to new challenges and use cases. The chips would remap themselves to be more powerful, and the battery would regenerate.

Of course, this is the stuff of fantasy, but it would look a lot like the T-1000 character in Terminator 2. You remember this shape-shifting robot, right? It used the fictional mimetic polyalloy to transform into any person or object.

Hardware and software that could adapt constantly to the world around it would be miraculous.

Your T-1000 brain.

You have a three-pound miracle like this right inside your skull.

“Yeah, yeah,” I can hear you say. “The brain is amazing, blah, blah, blah.”

Hear me out. Yes, the brain is amazing—clearly the most remarkable three pounds on Earth. But the elegance of the design is even cooler than I realized (before my research for this letter).

Much like the kidney, faced with a seemingly unsolvable problem, nature created the ultimate elegant solution when it created the brain.

To explain this, let me ask you a question: Imagine you could transport an exact replica of your one-day-old self back in time 30,000 years—the exact body, brain, and DNA you started life with. As you grew up to say, at age 10, do you think you would have the ability to use language to communicate?

My guess is that you realize the answer is "no" because the Paleolithic hunter-gatherers of that time did not speak any languages. This appears obvious, but consider that your one-day-old self had the DNA and the brain architecture in place to learn and use language (which is a very advanced capability). So, unlike other species, you had the capacity to speak, but raised in a non-verbal society, you never uttered a sentence.

Now imagine the 10-year-old you, raised by hunter-gatherers, catapulted back to modern times. You are suddenly surrounded by people talking endlessly about college football and real housewives.

Do you think you woud eventually learn to speak, expressing your opinions on why the coach failed to call a critical timeout?

The answer here is also “no”.

If you are not immersed in an environment where language is spoken from birth to age seven, you will never learn to speak.

Tragically, a modern example of this is the gut-wrenching story of the girl in the window. Danielle Crockett was discovered in Florida in 2005. For the first seven years of her life, she was locked in a small room with no human interaction. When she was rescued, she was incontinent, could not speak or make eye contact, and could not chew solid food. Despite years of therapy and care after this, she did not develop functional speech. One year later, she still had not mastered using a sippy cup. (Extensive testing showed she had no genetic problems such as cerebral palsy, autism, or Down syndrome.)

Nature’s big gamble.

The kidney faced the challenge of being unable to predict which toxins would need to be filtered in different environments and eras. The elegant solution: filter everything, then add back the things you need.

In developing the human brain, nature faced a different intractable problem: How do you design a species that can adapt and thrive in nearly any environment?

For comparison, consider the Komodo dragon. He's a dragon, so that is pretty badass. His dragon brain does excellent work when he is living in his dragon empire. But if we airlift him to Detroit, he won’t make it. He can’t adapt.

So how do you solve for this fatal limitation? How do you design a brain that can adapt to any environment, including those you can't imagine today?

You create the ultimate elegant solution: You allow the environment itself to design the brain.

And unlike the kidney, you allow the environment to shape both the hardware and the software of the brain.

Here’s the thing. I knew the brain was adaptable. But before researching this idea (which I was doing as part of my larger thinking on how the brain experiences time and encodes memories), I truly did not understand the degree to which the human brain starts as a blank slate.

Like a chameleon, the physical architecture of your brain grows through childhood to literally reflect the world around it.

Your DNA sets the rules. Distinct brain regions are biologically predisposed to certain capabilities (like language). But nothing about how your brain actually emerges is preprogrammed. It is all designed and constructed in real time via direct experience with the physical and social world you grow up in.

As one more tragic example from Danielle Crockett’s experience, after her rescue, she was unable to see anything in the distance. For seven years, she only experienced physical objects close to her. The brain region with the capacity to translate signals from the eyes showing objects in the distance never developed for Danielle. The physical architecture for this ability did not grow because this type of input did not exist in her lived experience.

To think about this in more literal terms, consider that the human genome has about 20,000 genes. But our friendly Komodo dragon has about 19,000 genes, not much different from us.

The dragon’s genes give it a fairly complete set of instructions to live a nice dragon life. Those DNA instructions help direct the 100 million or so neurons in a dragon's brain.

Meanwhile, the human brain has about 86 billion neurons and about 100 trillion synapses (connections between neurons). This allows for 10¹⁵ possible network states in your brain. I’m pretty sure that’s a lot.

"So how does the massively complicated brain, with its eighty-six billion neurons, get built from such a small (DNA) recipe book?” David Eagleman asks in Livewired (the primary content source for today’s letter—it’s fantastic).

“The answer pivots on a clever strategy implemented by the genome: build incompletely and let world experience refine. Thus, for humans at birth, the brain is remarkably unfinished, and interaction with the world is necessary to complete it.”

This strategy is an evolutionary gamble because failures or inadequacies of experience will leave the brain undeveloped and unable to function. It also takes a lot of time, during which human babies require external care to survive.

But the payoff is huge—an elegant solution that, by definition, is adaptable to any environment.

The sensitive period.

As you saw in Danielle Crockett's case, there are specific time windows for brain development. Eagleman describes these as doors that open and close; when these developmental doors are open, different parts of the brain and different human abilities must be built.

For example, there is a critical period for language development (0-7 years) where children learn languages without any instruction. They mimic accents, absorb grammar structure intuitively, and acquire vocabulary rapidly. Through this environmental exposure, babies lay down foundational neural architecture (physical changes to the brain).

Next is the "sensitive period" from roughly 7-13 years old, when you can pick up new language and accents and be somewhat similar to native fluency. From puberty on, learning new languages requires effort, and you can only add additions and subtle alterations to the foundational language architecture constructed in your early years.

Continuing the Terminator theme, Arnold Schwarzenegger moved to the US at age 21. No amount of practice will ever overwrite his Austrian accent or speech patterns.

Neuroscientists call these periods when the doors are open for deep brain mapping “sensitive periods”. These doors do not open and close at the same time, as shown below.

Some doors never close.

Today’s letter is meant to provide a foundation of understanding for future concepts I want to explore. While the foundational architecture of your brain was constructed from your lived experience as a child, your brain continues to change every day. These are not merely software changes. New ideas, experiences, challenges… they all change the physical structure of your brain.

While some aspects of brain growth and adaptation stop as you age, other parts of your brain wiring are continually changing. The idea that your brain can change and then retain its structure throughout life led the psychologist William James to coin the term "plasticity". The beauty of plastics is that they can be shaped and then hold that shape. This is where the term brain plasticity (or neuroplasticity) comes from.

Eagleman finds this term incomplete because it suggests the brain changes and then holds that new design. “But that’s not what the brain does. It carries on remolding itself throughout your life,” he explains.

Eagleman introduces the term “livewired” as a better way to think about how the brain continually evolves. “It becomes impossible to think about the brain as divisible into layers of hardware and software. Instead, we’ll need the concept of liveware to grasp this dynamic, adaptable, information-seeking system.”

The T-1000 worked better than the original Terminator design because it could alter its hardware (physical shape) and its software (knowledge, skills, memories) in response to changing environments. That is also the true miracle of your brain.

“Every man is born as many men and dies as a single one,” Martin Heidegger said (which now makes sense to me, at last).

In future letters, I will build on this foundational idea to highlight what aspects of your mental adaptability are largely closed by midlife (where the sensitively doors are closed) and which remain very much open and ready for growth and change.

I'll also tell you what we can learn from 678 Catholic nuns about the concept of cognitive reserves and how this can counter the threats of dementia as we age.

“The thrill of life is not about who we are but who we are in the process of becoming,” Eagleman says. “Similarly, the magic of our brain lies not in its constituent elements but in the way these elements unceasingly reweave themselves to form a dynamic, electric, living fabric.

“Just a handful of pages into [this newsletter], your brain has already changed: these symbols on the page have orchestrated millions of tiny changes across the vast sea of your neural connections, crafting you into someone just slightly different than you were at the beginning of this [letter].”

Thanks for reading today.

Have a great Sunday,

Kevin

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