There is no such thing as a brain transplant. By this, I don’t mean that the technology doesn’t exist to transplant a person’s brain to another person, though I don’t think our technology is at that point yet. What I mean is that if I somehow transplanted my brain to another body, this procedure wouldn’t be a brain transplant. It would be a body transplant. After the operation, I would wake up in a new body, and presumably have to learn to use new eyes, arms, and other sensors and activators. In this sense, my body is part of my identity no more than my car is. Both are familiar machines that I’ve grown accustomed to, but my brain is what is really me. (Of course, one could apply similar reasoning to conclude that, since I’m still me if you remove any single cell of my brain (and no others) that none of my brain is actually me either.)

Let’s assume that our minds are physical just like everything else in the universe. To assume otherwise would mean we’d have to address the interaction between the physical and the non-physical, since brain damage and drugs show that physical processes can affect our minds.

That said, we are not our physical neurons, but the patterns that they encode. Douglas Hofstadter and Daniel Dennett describe a thought-experiment in which you replace your brain cells, one at a time, with functionally-equivalent silicon circuits. In this case, “functionally-equivalent” means that the external physical behavior of your silicon brain is identical to that of your biological brain. So, without looking inside your skull, I wouldn’t be able to tell the version of you that had a silicon brain from the version of you with a biological brain. I might also ascribe consciousness to the silicon version of you for the same reason that I ascribe consciousness to the biological version of you, which is that I am the only thing in the universe that I truly know to be consciousness –I just extend this trait to others because it’s more parsimonious to do so. We might also make an argument that from your perspective the silicon brain is still you. If we assume that, after a few days, we re-replace the silicon circuits back with your original neurons, each modified to account for the changes in the silicon circuits over that time (i.e., what they’ve learned), then we’ll get back to your brain, which (by the assumptions of the thought experiment) will be physically identical to your brain as if we had never done the silicon replacement at all. Your memories of the experiences of past few days living as the “silicon brain” would be identical to your memories had your biological brain experienced them. At any rate, from an outside perspective at least, what makes you you isn’t your physical neurons, but the patterns and information that those neurons encode. The substrate –biological neuron or silicon circuit– doesn’t matter.

Like virtually all concepts, the concept of “self” is merely an abstraction we throw on top of the atoms, quarks, or strings of reality so that we can talk about macro-scale phenomena, where macro-scale here means anything more than a handful of quarks, which is virtually everything in our day-to-day existence. And like all abstractions, we can find places where the abstraction of “self” breaks down. For example, suppose we perform the silicon-replacement thought experiment as above, replacing one neuron at a time with functionally-equivalent silicon, but after removing your biological neurons, we reassemble them into your brain in a copy of your body. Now, there are two yous. You might say that the “neural” you is the real you, but what if we used neurons instead of silicon in creating the brain of your first body? Then each copy would have equal claim of being the true self. At least, both copies would feel and believe the same about being the original you. A full discussion of what constitutes one’s self warrants another essay!

Suppose you wanted to live forever. Modern and future medicine might be able to replace your hips or even your liver, but all body parts wear out, including neurons. If I wanted to live forever, not only would I have to occasionally “replace” parts of my body, but I’d have to replace the neurons in my brain. One way to do this would be to clone myself, as in Robert Heinlein’s “Time Enough for Love”, then “upload” my thoughts, memories, etc. to my clone’s brain. Theoretically, the cloned-me could be behaviorally identical to the old me, with the exception that its joints wouldn’t be as arthritic, and it’d be all around in better shape.

If “you” are the patterns encoded in your brain, living forever would mean ensuring that these patterns continue. So what are these patterns that make you you? These patterns include things like your beliefs, memories, habits of mind, values, and desires. They also include your worldview and your ontology for how you characterize the world. For example, like many Americans, I associate dogs and cats together more than I associate either with pigs. In my mind, dogs and cats are pets, and pigs produce meat. This isn’t true for all cultures, some of which don’t eat pigs, and some eat dogs. Some of my associations have a more personal bias. For example, I have a stronger association between cats and mosquitoes than I assume most other people do, because I have fairly strong allergies to cats, and both cats and mosquitoes have made otherwise pleasant occasions less so for me.

Where do these patterns come from? These patterns have only two possible sources: genes and environment. Psychologists debate the general contribution of each of these. We might gain some perspective of the possible influence of genes by noting that our brains have on the order of 10,000,000,000,000 synapses, while the part of our genome that encodes our brain can be compressed to about 200,000,000 bits. This gives about 50,000 synapses for every bit of our brain’s blueprints. So, only so much can be encoded in our genes. What about explicit instruction (e.g., lectures and what we read)? If we hear 100 words per minute for 12 hours every day for 40 years, and we assume about 10 bits per word, this gives roughly 10,000,000,000 bits for natural language input, or about 1,000 synapses for every bit of natural language. This is 50 times more than what our genes account for. As to the question of what informs our synapses, there are still many unaccounted for bits. I suspect that genes and natural language are only the tip of the iceberg, and the iceberg’s underbelly is tacit knowledge learned through observations and interactions with others and with the world around us.

One way to live forever would be to upload your consciousness to silicon. But if that preserves “you”, then wouldn’t it also preserve you if you could regenerate a new biological brain and upload your thoughts and beliefs to it? My claim is that the process of having kids and raising them is doing something close to this. But kids are hardly clones of their parents. There are more than a few examples of staunch Republicans raising children who go to college and become radical leftists. I claim that the belief systems that make us us get stuck in ruts, and that kids are a way of resetting this. I further claim that most of our belief systems are deep and tacit, and that more measurable beliefs, such as political leanings, are relatively superficial. Therefore, kids allow us to retrain our belief systems. By interacting with your kids, they copy the important parts of your beliefs and habits.

What do I mean that belief systems get caught in ruts? One example is my addiction to Emacs. During college, I learned to use the Emacs word-processor, and over the past 20 years, I’ve gotten to the point where it’s difficult for me to write prose or programs using any other word-processor. This was fine in the late 1990s, but Emacs is starting to become dated. Emacs uses a large number of arcane key-combinations, and these have become entrenched in my muscle memory. For example, pressing the “control” key at the same time as the “k” key deletes the text from the cursor to the end of the line the cursor’s on. When I habitually type this while composing an email in Gmail, it tries to create a link. Maybe I ought not to upload the Emacs key-combination habits to my clone. My speaking accent has also crystallized into American English, and if I were to move to another country, I would always mark myself as American every time I spoke. Maybe it’d make sense to let the new me speak without an accent.

I also have many outdated beliefs. These are tacit, not explicit, so it’s not as simple as correcting a misunderstood fact. For example, I was raised Catholic, but I am now Atheist. To this day, 25 years after my conversion, I’m still digging up beliefs that are rooted in Catholicism. For example, Catholicism believes in an afterlife and divine justice. One consequence of this is that a follower need not worry much about righting things while alive because God will judge all things. Another consequence of Catholicism’s belief in an eternal afterlife is that our time on Earth is mostly preparation for the afterlife, which at infinity years vs. 80 odd years is what our existence is really about.

Many of my tacit beliefs and patterns need updating, but they’re so interconnected that it’s difficult to change just one thing. In Korea, there is a system of heating called “ondol” which means warm stone. Korea gets quite cold in the winter, and apartments are frequently heated through floor heating. One consequence of this is that many people spend a lot of time on the floor of their homes. People sleep on the floor and regularly sit on the floor during meals. No one wants to sit on a dirty floor, so it’s custom to remove one’s shoes immediately when entering a home. A consequence of this is that Korean shoes tend to be easy to slip on and off. Also Korea doesn’t have as much need for home furniture like beds and kitchen chairs. The point is that one pattern of behavior can become entrenched with others so that changing a simple thing, like wearing Doctor Martin boots (which take a long time to lace up) would put pressure to change many other behaviors.

These sorts of behaviors exist on a family-sized scale as well. It wasn’t until I was in my late teens before I realized that my own family has a custom not shared by everyone. It’s about dealing with trash in the car. My parents never explicitly told me all the rules of the custom, but this is how they (and now I) deal with trash while driving: keep a durable plastic bag of a particular shape and size hooked on the gear shift and hanging to the passenger side. These bags might be the sturdy bags you might get at a gift shop. When you stop for gas, empty the bag into the gas station trash, but keep the bag. Why keep it? Because they’re hard to come by. Why not just use a regular grocery plastic bag? The shape of the holes on these bags are such that they hang so that it’s difficult to put trash into with one hand while driving. Since you keep these bags a long time, you don’t want to put trash into them that might stink up the car. For example, you can’t just put an apple core into it. Instead wrap the apple core in multiple tissues before putting it in the bag. Again, this is a small coherent system (and also an example of a tacitly passed habit).

Why is it hard to change beliefs? When learning, we build things in terms of concepts we already know. It becomes difficult to change an underlying concept with so much built on top of it. I’ve heard that there exist some nuclear power plants that still have 1950s control systems, with 1960s controllers on top of those, and even more modern control built on top of those. The issue is that you can’t take the plant offline to unplug the controller. You have to start with a clean slate!

We can get another view of why a “reset” might be necessary by considering what it would mean to live for centuries. For example, consider the scars a 10,000 year old man might have. Over the course of several hundred years, one is sure to break some bones and break their skin. Both of these would become filled with scars in the same way that the surface of the moon is pocked with scars from eons of asteroid strikes. These are only the scars we can see. Surely, entropy would make its mark on that person’s internal organs.

And what about his cognitive state? Is there some sort of local optimum or cognitive aging analogous to memory leaks in computers, where the most practical solution is to reboot? You’re a different person than you were 20 years ago. Imagine if you lived for thousands of years. Would you reach a fixed-point, or would you continually change depending on your context. If it’s the latter, then like the ship of Theseus, even the patterns that make you you might be replaced such that the set of patterns that comprise you at one time are completely disjoint from your “pattern set” at some time in the future. At this point, you might say that you are some meta-pattern that holds constant during that span.

If you lived for thousands of years, would you notice patterns that can’t be seen otherwise, or is cultural transmission powerful enough to find these patterns? For example, written and oral history allows historians to find trends in empires that span centuries. On the other hand, firsthand experience is often difficult to replace, and no one had firsthand knowledge of the entire Roman Empire. Even if a person could live long enough, he couldn’t be present at all events, as important events often took place simultaneously hundreds of miles apart.

Main points:

  • We are patterns.
  • We can upload these patterns to other systems, including computers and other people.
  • People can acquire mental cruft, so “rebooting” has an upside.
  • Our kids capture the fundamentals of our patterns, not the specifics.
  • The bulk of our patterns are tacit, and are learned through years of observations and interactions, as opposed to explicitly taught knowledge.


  1. In a sense, an adult is a being thousands of years old, or has nearly the same Weltanschauung as if he lived for thousands of years. Conversely, figures from antiquity, such as Marcus Aurelius are still living, though distributed among millions of cognitive descendants.

  2. You can upload your thoughts to other people, your kids just naturally learn from you, so are a fist candidate. Isaac Newton died childless, yet his ideas live on.

Addendum 2017/05/12/20:19

I got a new computer today and spent more time than I should have transferring my files from one computer to the other. The hardware wasn’t exactly the same, so a rote copy wouldn’t work. I had to monitor the files a little. I was surprised at how much “cruft” had built up in my old computer. I didn’t copy most of this to the new computer.