I once heard somewhere (I know I don’t need a cite) that the human brain is the most complex thing in the known Universe. Yet it is stored on what might be one of the comparably smallest things in the known Universe: human DNA. DNA can literally be written over and over again on the head of a pin.
How is this possible?
Actually, if you want to know how I came up with this question, it was while reading this Wikipedia article on the “replicator” from the fictional Star Trek Universe. This article claims:
If I understand this article, it is impossible for replicators to store that much information. But doesn’t human DNA already resolve this problem somehow?
Because DNA is more of a recipe than a blueprint when building such organs. It doesn’t directly detail most of the details of how to grow a brain; it runs a collection of processes that when all goes well will result in a brain being grown. There’s no central plan being consulted, just a collection of cells executing genetic instructions according to a procedure.
The DNA stores the information for your brain in the same way that a manifest of building material stores the information for your house, or an HR filing cabinet stores the information for your company.
The complexity arises out of, and is stored within, the entire system, genetics and proteomics.
DNA gets a lot of attention, because it represents a relatively simplistic and accessible point for us to interact with biology (of course that’s a heck of a relatively :D), but it’s only a part of the picture.
I recently wrote an article HERE, that ended up talking about exactly this.
I think it’s more obvious when you look at something like blood vessels.
They form a very intricate web; precisely specifying the paths of all vessels would take a sizable number of A, C, G and Ts.
But instead, beyond the major vessels, there is probably some kind of fractal process that ensures that every volume of living cells is suitably supplied. And/or chemical signalling by “deprived” volumes results in new vessels spawning.
The complexity of the brain comes about in similar ways.
You’re thinking (heh) of DNA as a book or USB memory card which carries a one-to-one schematic for building a human body. Don’t.
Think of DNA as a recipe- one which, when followed exactly and in exactly the right environment, gives us a human. A souffle recipe is actually a fairly simple thing; just a few ingredients, right? But if you mix them together in exactly the right proportions in exactly the way the recipe tells you to, and then bake it for exactly the right amount of time at exactly the right temperature…
You end up with something which is more complicated than the recipe would indicate. The recipe doesn’t tell you how, exactly, you get the right consistency, the right amount of fluffiness which tastes exactly the way it’s supposed to… but if you follow the recipe, you’ll almost always get the result you want.
Think of DNA as a recipe, and the environment that the egg and the sperm are combined (the womb, and the entire life support system of the mother) as the oven. And even then it doesn’t always work out. Change the temperature at a certain point during an alligator’s gestation, and it’ll change sex from female to male, for example.
Identical twins have identical DNA but far from identical brains. I know one pair of twins (actually I knew only one of them). The one I knew studied math, won a fancy fellowship and got an MSc and then dropped out, became a writer for a throwaway weekly, then a translator. A career never really gelled. The other studied physics, won the same fellowship, got a PhD, got a job and is now a very well-known physicist. The reason I recount this story is by way of showing how far the DNA is from being a detailed blueprint.
This little nugget just screams ‘factoid’.
Granted, the human brain is plenty complex. A bunch of them working together with some artifacts and apparatus thrown in (a football team, a culture, a corporation, a sorority, an IT team, a lynch mob, an orchestra, an economic system) however is much much more complex. Add some other living things, some with brains (an ecosystem, the Earth) and it’s even more complex. Plunk the whole mess down amid a bunch of other stuff rotating and spinning away (the Solar System, the local group, the whole of the physical universe), and you’ve got something much more complex still.
(Looks like a fight between people employing some special pleading via various ad hoc understandings of the word “object” on the one hand and people with the correct answer (“no”) on the other. But I digress.)
Remember a brain is a massive collection of multiconnected neuron cells like a mess of spaghetti. (And this is a masive simplification). Between any pair is a connection, and this connection depending on use can be more or less conductive. This is how thinking and memory etc. work. So to reproduce Captain Kirk exactly, up to his memories and character, the transporter device must reasseble every tiny detail of his brain and every interconnect in just the right place with just the right amount of connectivity. However, DNA simply needs to grow a fresh brain with its own unique and totally random spaghetti pot of neurons - fill this lobe with these sorts of neurons, a blank slate of a brain following the same sort of semi-random pattern as the fractal vein example above.
18 years of child-rearing and education then turns that random mess into something that (we hope) can think for itself; but each one is unique and different, the myth of fingerprints.
You can also look at how human DNA came to be, through evolution. Our ancestors were independent single celled little critters. Bit by bit over billions of generations there were little changes to the DNA that made a new creature that did new things. Eventually cells reproduced and stuck together to form multicell critters. And bit by bit they changed over generations, until we arrived at humans. But it was a process of trial and error that had many many errors for each success. So the human brain comes from DNA that once was much simpler and only through billions of permutations did the human being emerge.
It is incredibly complex though. The DNA not only contains the instructions for creating every part of a human being, but it also has the instructions for maintaining and reproducing the incredibly complex cell machinery that forms every part of us.
Here’s the analogy I would use to explain it: Facebook is an enormously complex web of interactions between hundreds of millions of people. However, the Facebook software’s source code only contains the method of storing and making connections. The data and connections themselves are not part of the source code. If you think of brain cells as the data, and connections and the source code as the DNA, it’s the same idea.
I really like dracoi’s analogy. An unused brain is not very complex in a mathematical sense, because it is specified by a fraction of the number of bits in a human genome. The information in the human genome (at most 750 MB) would fit easily on a CD, so the mathematical complexity of the structure it specifies must be less than that. The structure of the brain looks naively to be much more complex than that, since to specify the coordinates, shape, and interconnections of each neuron would require far more bits. The reason for this is that there are rules of structure that we don’t know. One of the rules for a growing neuron, for example, appears to be: “If you see a bunch of neurons growing in some direction, follow those guys!” This leads to structure that appears to be much more complex than it really is, in a mathematical sense. The genes code for these rules, not for the final structure.
But it is also clear that an adult brain must be much more complex than those original few hundreds of megabytes. The rest of the complexity comes from the operation of the brain on the stimulus it receives from its environment. The total complexity is a matter of debate. There are about a billion neurons, each with thousands of synapses, each with some number of bits representing its strength. This leads to estimates in the range of a few terabytes or more.
Draw lines connecting each marble to its 5 nearest neighbors within a 5 cm radius.
If any marble has less than ten lines connected to it, remove it.
Look at how complex a pattern you have just generated with those three rules. You can add more complexity by connecting that 1x1 meter space with the one right next to it, or the one three spaces over, or by letting the marbles move in between steps, etc.
