The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [31]
Chemically building these structures molecule by molecule is remarkable in itself. What is truly amazing is that the structures assemble themselves. In fact, this is the only way nanotechnology works. There are very few molecules chemists can manipulate one at a time, putting one next to another and then gluing them together. All they can do is set up the right soup of molecules milling around randomly (“thermodynamic noise”) and then wait while the desired structures are built by processes that emerge from the operation of the laws of physics. Just by changing the flexibility of small molecules of DNA in the starting soup at the bottom of the test tube and changing their concentrations, chemists can produce many different three-dimentional objects, including tetrahedrons, dodecahedrons, and buckyballs—soccer ball shapes built out of DNA molecules. Of course, what we can do in the lab, unguided nature can do better, given world enough and time.
Replication by template matching is even easier than self-assembly. And it works particularly well under conditions that the second law of thermodynamics encourages: the larger the number of molecules and the more randomly the molecules of different kinds are distributed, the better. These conditions increase the chances that each of the different atoms needed by a template will sooner or later bounce into it to help make a copy. In fact, “works well” is an understatement for how completely template replication exploits the second law.
Let’s assume that the mixture of atoms bouncing around in a test tube or in nature is very disorderly and getting more so all the time, as the second law requires. As the disorderly distribution of atoms increases, the chances of different atoms landing on the template increase, too. Most of the time, an atom bouncing into a template of other atoms is too big or too small or too strongly charged to make a copy molecule that survives. Even if the new atom bonds to the others, the whole copy may break apart due to differences in size or charge or whatever, sending its constituent atoms off to drift around some more, increasing entropy, of course. In most cases, in the lab and out of it, this disorderly outcome of instability in copying is the rule, not the exception. The exception is a successfully duplicated molecule.
Now let’s add some variation to the replication. In effect, we are introducing mutation in template copying. Variation is even easier to get going than replication at the level of molecules. It’s imposed on molecules during the process of replication by some obvious chemical facts working together with the second law of thermodynamics.
FIGURE 2. The right side of the periodic table
of the elements
One look at the columns of the periodic table of the elements (Figure 2) is enough to see how disorder makes chemically similar but slightly different molecules. In the table, fluorine is just above chlorine in the same column. They are in the same column because they react with exactly the same elements to make stuff. Chlorine and sodium atoms bond together and make table salt; that means that fluorine and sodium atoms will bond together, too (the resulting molecule is a tooth decay preventer). The reason fluorine and chlorine atoms combine with sodium equally well is that they have the same arrangements of electrons that do the bonding. All that means is that if a chlorine and a fluorine molecule are both bouncing around and bump into the same template, they may both bond the same way with other atoms on the template to make similar, but slightly different molecules. A template with chlorine molecules in it could easily produce a copy molecule that differs only in having a fluorine or two where a chlorine would normally go. Voilà! Variation.
FIGURE 3. Molecular variation in action:
sugar versus Splenda
Here is an example of slight molecular variation with vast consequences. Sugar has a somewhat