What do we learn about the world by having you (or Dennett, or Wilson, etc.) sit in your armchair and proclaim that whatever happens in the brain must *somehow* be explainable within the laws of physics, and then dismissing people who rightly ask for a demonstration by saying that it is something incredibly complicated and unknown?
Consider a very simple computer with, say, 256 bytes of memory. Load an arbitrary program into it and start the computer running. How long will it run before reaching a particular state? Will it ever reach that particular state?
Alan Turing showed that, for an arbitrary starting state, there exists no closed-form analytical answer to these questions, not even in principle. There are some simple states for which answers may be derived analytically, but for the remaining states there are no such analytical answers. Once an information processing machine reaches a certain level of complexity, the only way to tell what it is going to do is to start it running and watch what happens. This is the famous Turing Halting Problem.
So you don't even need metaphysics, psi powers, or the existence of a deity for the brain to be unfathomable. All you need is neurons which act like information processing elements, and the neurons must be connected such that information loops back upon itself in patterns that have a little complexity. From the halting problem point of view, the amazing complexity of the human brain is pretty much an absolute guarantee that its behavior will be difficult to predict. Of course, the brain is not a random noise generator, so you can measure its behavior over time and predict what it will tend to do under certain conditions.
But that leaves the other question -- whether neurons arise from plain old chemsitry -- unanswered. I think it's a reasonable working assumption to make. Researchers have studied and modelled numerous biological systems, and not only have they all ended up being ordinary chemistry, there hasn't even been the slightest hint that unexplained forces are at work. Moreover, there is no behavior at larger scales that cannot be readily ascribed to chemistry: people are not clairvoyant, they do not teleport instantly from one place to another, etc. Of course, there can be no absolute proofs in matters like this. You cannot disprove the existence of god, all you can do is point to a vast pile of experimental evidence completely lacking in evidence for him.
My late cat has the following property: if you let it fall from the ceiling of a tall building on planet Earth, it will accelerate towards the planetary surface at a rate of 9.62 m/s/s. How does this property follow from the DNA of my late cat?
The bulk properties of organisms are functions of their DNA in exactly the same fashion as their chemical and microscopic properties. And you're rather inaccurate: the cat will not, in fact, accelerate at a fixed rate. Its acceleration will decrease asymptotically until it reaches its terminal (ha ha) velocity. Actually, even that's not quite correct: it will tumble, flex, and sway in the wind, and it's instantaneous speed will vary. The average terminal velocity will be stable, however, and will be a function of muscle tension, skeletal structure, skin "flappiness", and hair drag. In particular, muscle tension will be a strong function of brain behavior, and thus the terminal speed of a cat depends on its psyche.
Let's look at muscle tension in more detail. A cat dropped from a great height suffers from panic in the first moments. Its muscles tense as a direct result of the panic. This is a strong effect, and seems more or less inevitable. If the cat strikes the ground while its muscles are tense, its body will not give; tendons, muscles, and ligaments will be ripped to shreds; and bones will be broken. Curiously, after a moment of falling, the muscles relax. If the cat strikes the ground after the muscles relax, it will be floppy and injuries will tend to be much less severe than if it had struck during the "tense" phase. This effect has been verified experimentally in injuries to pet cats that fell out of skyscrapers, by correlating severity of injuries to height of residence: cats from lower floors tend to be more severely injured. If we were in an evolutionary psychology mood, we might ascribe this to evolution having gifted the cat's brain with the ability to recognize falling and override the panic response. Since cats are famous climbers, such a response would increase fitness, and is consistent with the observations.
Let's go back to the accelleration of dropped animals, and replace the cat with some other types of tetrapods. For instance, we could try the experiment with a particular species of squirrel, one that has flaps of skin between its legs, the skill to manipulate and stretch those flaps, and a strong innate desire to fling itself out into thin air. This is, of course, the flying squirrel, and because of its DNA it would accelerate much slower than a cat and have a much slower terminal velocity. The way it is built even gives it the capability to land softly and survivably. Such a difference from the cat, or even the other squirrels, and all from having somewhat different DNA.
Try the experiment with another tetrapod: the bat. It might accelerate downward at considerably greater than one gee, hover, accelerate upward, or anything in between. It contains carbon, a cat contains carbon. It is powered by ATP, a cat is powered by ATP. It shares many chemicals and hormones with a cat. So why such a drastic bulk physical behavior? DNA.
Of course, that's a toy example. There's all sorts of properties any organism has which have *nothing* to do at all with DNA. Like, e.g., having a scratch on a particular day, or being a widow.
The very concept of a scratch is predicated on the existence of a keratin-rich epidermis produced by -- yep, you guessed it -- our friend DNA. And, while the existence of a particular scratch may not be an obvious result of the activities of DNA, the frequency and severity of scratches are strongly dependent on DNA-derived properties. E.g., hemophiliacs tend to have fewer, less-deep scratches than non-hemophiliacs; people with a strange love of roses might tend to have more scratches than non-rose lovers; and people with thick, tough skin will have fewer, less-deep scratches.
I don't want the world, I just want your half.
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