I was reading something from Asylum Seeker at Madman’s Paradise where the whole concept of “random” came up. This was such a pivotal point in a course I took on Macroevolution (yes, it is a course), that I must talk about the idea of “randomness” in terms of mutations.
Mutations are not “random” as is typically defined by a lay person for a number of reasons. Namely, some portions of the chromosome are more prone to mutation than others. Since cytosine does occasionally spontaneously deaminate (lose an amine) into uracil, and one of the commandments of genetics is “Thou shalt not have RNA in DNA,” cytosines are far more likely to result in single nucleotide mutations in the replacement process. Thymine dimers can also result in mutations as well. These events are not equally probable. While mutations do occur nonspecifically, they are still, when talking to a lay person, not “random,” but more probable in some respects than in others. Regions of DNA are also more likely to undergo mutations than others for as yet unknown reasons. This probable has something to do with proofreading of DNA around methylated histones. Regions of DNA with suppressed expression are more likely to have mutations missed.
Randomness also has nothing to do with evolution. Evolution, in fact, is the opposite of random, however, it is random on the sense that it is unpredictable. It is not unpredictable because it is random, it is unpredictable because the conditions (genetic, developmental, environmental) which result in selection cannot be predicted. We can predict how a single population will change based upon present condtions and selective pressures, however these pressures can change rapidly and without warning. Similarly, the developmental characteristics can change rapidly given temperature changes, rainfall changes, and other climactic changes. These are (at present) impossible to predict. As such, what we mean when we say “random” mutation and selection is, in fact, just a means of saying “we currently cannot predict this, so we shall call it ‘random.'”
So, what does it mean when lay person describes something as “random?” The most frequent usage I’ve heard is “lack of order, purpose, cause, or predictability.” A more accurate definition is “following a pattern which cannot be predicted given current tools.” We may, in fact, be able to predict mutations, selection, genetic drift, and evolution. This will probably not exist within our lifetimes.
How, then, should we describe evolution of biological organisms? Quite simply, we must rely upon the understanding of a concept (evolution) which many people have absolutely no formal eduction in and very little informal education of. What we mean by “random” does not fit with what we know about mutations. Mutations, as previously stated, have probabilities associated with different locations on the chromosome as well as different nucleotides and sequences. So saying it is “random” doesn’t fully explain that we can, to some degree, predict where mutations will occur.