The Atheist's Guide to Reality_ Enjoying Life Without Illusions - Alex Rosenberg [39]
The physical facts—the starting conditions at the big bang plus the laws of physics—fix all the other facts, including the chemical and biological ones. All the laws of physics except the second law work backward and forward. So every one-way process in the universe must be driven by the second law. That includes the expansion of the universe, the buildup of the chemical elements, the agglomeration of matter into dust motes, the appearance of stars, galaxies, solar systems, and planets, and all other one-way processes. And that will eventually include, on one or more of these planets, the emergence of things with even the slightest, merest sliver of an adaptation. We can put it even more simply. In a universe of things moving around and interacting on paths that could go in either direction, the only way any one-way pattern can emerge is by chance, here and there, when conditions just happen to be uneven enough to give the pattern a start.
These rare one-way patterns will eventually peter out to nothing. Trust the second law. Consider the one-way process that built our solar system and maintains it. It may last for several billion years. But eventually, the nice pattern will be destroyed by asteroids or comets or the explosion of the sun or the merging of the Milky Way with other galaxies, whichever comes first. That’s entropy increase in action on a cosmic scale. On the local scale, entropy increase will occasionally and randomly result in adaptive evolution. And that is the only way adaptations can emerge in a universe where all the facts are fixed by the physical facts.
Because entropy increase is a one-way street, the second law is also going to prevent any adaptation-building process from retracing its steps and finding a better way to meet the challenge at hand. Once a local adaption appears, it can’t be taken apart and put together in different, more efficient, less entropy-increasing ways. The only way to do that is to start over independently. Adaptation building produces outcomes that get locked in, to be worked around in the creation of new adaptations. Natural selection is famous for producing such examples of inferior design, Rube Goldberg complexity, and traits that could only have been “grandfathered in.” It’s not just the oft-cited example of the blind spot in the mammalian eye resulting from the optic nerve’s coming right through the retina. An even more obvious case is the crossing of the trachea and the digestive system at the pharynx—convenient only if you like choking to death. We think of the giraffe’s neck as an adaptation par excellence. But the nerve that travels from its brain to its larynx has to go all the way down the neck, under the aorta, and back up—a 20-foot detour it doesn’t need to take.
Any adaptation-creating process has to produce suboptimal alternatives all the time. It has to do this not just to ensure entropy increase but to honor the one-way direction that the second law insists on. Perhaps our most powerful adaptation is the fact that our brain is very large. It has enabled us to get to the top of the carnivorous food chain everywhere on Earth. But this is only the result of a piece of atrocious design. The mammalian birth canal is too narrow to allow large-brained babies to pass through. This bit of locked-in bad design meant that the emergence of human intelligence had to await random changes that made the skull small and flexible at birth and thus delay brain growth till after birth. This is where the large fontanel—the space separating the three parts of the infant’s skull—comes in. Now the kid has room to get through the birth canal and has a skull that will immediately expand afterward to allow a big brain to grow inside it. But brain growth after birth introduced another huge problem: the longest period of childhood dependence of any species on the planet. All this maladaptation, corner cutting, jury-rigging