Tuesday, December 14, 2010

Sean B. Carroll, The Making of the Fittest (2006)

This is a wonderful book to read following Genome (November 27, 2010 post). It tells another set of stories derived from sets of three-letter words utilizing combinations of the letters of A, C, G, and T. Published just seven years after the publication of Genome, and written just as the human genome was in its final stages of being decoded, The Making of the Fittest reveals just how much more we have learned about our DNA in such a short period of time.

Sean Carroll is the author of another book, previously published, Endless Forms Most Beautiful, which documented the genetic source of both embryonic development as well as physical development outside the embryo after birth. I cited this book in the previous post.

The key words in this volume are chance, selection, and time. As someone who was intrigued and stimulated by French biologist Jacques Monod's book, Chance and Necessity, almost 40 years ago, these three words, and Carroll's interpretation of them in the context of what we now know about DNA and evolution, reaffirm what I have long-believed about randomness and causality: that events in the universe (biological, chemical, and physical) are both random and determined and there is no flawed incongruity in saying so. While randomness may appear to be a function of limited foresight --- cognitive uncertainty and unpredictability, as Ridley suggests in Genome, randomness is neither predestined or (intelligently) designed. Yet hindsight informs us that these same events are part of a causal sequence, many of which are quite orderly and repeatable.

Prior posts on this blog reveal that I am a skeptic of the intelligent designer thesis. (See May 24, 2010 and May 12, 2010 posts). The Making of the Fittest is probably the most devastating condemnation of intelligent design ever published. One cannot read and understand this book without coming to the conclusion that it is simply impossible for any type of intelligence to program life and contemplate mutation and evolution in the manner that it actually occurs. While those in the intelligent design community believe that it is impossible to contemplate the complexity and variability in life without an intelligent designer (a code for God), Carroll demonstrates that it is impossible to contemplate the complexity and variability in life as the output of a design. Theists will condemn this statement as the view of someone who believes that life has no purpose: but theists misunderstand and confuse purpose, which is a psychological event, with random mutation, which is a biological and informational event.

Both Carroll, Ridley and many others have reported that there is a universal common ancestor of all species dating back to billions of year ago, and the species alive today all share common DNA and RNA in their respective genomes that has been copied, translated, inherited, and preserved over the eons. What makes species differ is variety in the genome, and "[t]he source of all variety is mutation." Carroll notes that mutation has several connotations that have led to false impressions about mutation: first, that all mutation is bad and is not creative, and second, that if mutations are random (which he says they are), then a random process cannot account for all the complexity we find in living things today. "This misconception is based upon a failure to distinguish between mutation and selection. The mutational process is blind, natural selection is not. Mutation generates random variation, selection sorts out the winners and losers. Furthermore, natural selection acts cumulatively," says Carroll.

And there are a variety of mutations of the genetic code. The most common is the equivalent of a typographical error in the process of copying the genetic code --- a substitution of one of the four letters for another. But there are also mutations involving deletions of code and insertions of repeating code or duplications. Sometimes these mutations actually mean something --- changing something about the phenotype in which the genetic code resides, but many, many times these changes mean nothing --- they don't change a thing about how the gene works. Some genes simply lose their meaning over time because they are no longer used, and these are called fossil genes. And some mutations that do have meaning simply do not survive to live another generation because selection is neither accomodating nor forgiving. When mutations occur repeatedly and have meaning --- in the sense that it changes something about the phenotype in which it resides --- and selection favors the survival of that mutation, then given enough time (many generations, thousands of years) we can find new species evolving. Carroll has reduced his mantra of chance, selection and time to this expression: "i) given sufficient time, ii) identical or equivalent mutations will arise repeatedly by chance, and iii) their fate (preservation or elimination) will be determined by the conditions of selection upon the traits they affect."

The Making of the Fittest illustrates this proposition through several well-documented examples, but the star in this story are the genes that code for proteins that develop opsins found in photoreceptors in the eye. Opsins are involved in vision and in converting a photon of light into an electrochemical signal that is transmitted along neural pathways --- in humans to the areas of the brain responsible for vision. These genes and their predecessors are very old, and selection has operated on mutations of the genetic code that develop opsins to cause different species to have varying levels of visual acuity, color recognition, and other funcitonal properties.

Life can be described in terms of both variation (complexity) as well as order -- by which I mean that there is repetition and some level of stasis. For some, it is unfathomable that complexity and order can exist absent some intelligent designer. But biological science, chemistry, and even physics establishes that variation and order in living things exist quite well without a designer. Monod's "necessity" is a matter of selection, and for very long periods of time external conditions --- natural environment, predators, and even a given specie's social environment --- are relatively static leading to little or no change that gives rise to the appearance of order. Much in the process by which genetic code is copied over and over again: there are few mistakes and faithful copies of genes are repeatedly made preserving the existing order of things. But beneath the surface of appearances, mutations occur, and these mistakes are not planned, they are not purposeful, and they are random.

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