04
Jan
09

Randomness

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.

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7 Responses to “Randomness”


  1. January 4, 2009 at 9:44 pm

    “Namely, some portions of the chromosome are more prone to mutation than others.”

    I did not know that! Learn something new everyday.
    I probably shouldn’t have brought evolution into the fray when talking about randomness at all. But, then again, it seemed to me to be a good example of how random and unpredictable behavior on one scale can have a nonrandom, predictable effect on a larger one. (Well, as you mentioned, predictable to a degree). But, I fear I may be out of my depths when trying to deal with these things beyond the rudiments.

  2. 2 jaredcormier
    January 4, 2009 at 9:47 pm

    Well, it’s not just you, even I am guilty of describing these things as “random” simply because it’s difficult to delve into these details with everyone.

  3. 3 Stacy S.
    January 4, 2009 at 10:08 pm

    Welcome back! 🙂

  4. January 4, 2009 at 10:08 pm

    Well, for the most part it works. Just turns out that the word is outright wrong when describing certain parts, and is only true in certain respects when looking at other parts. But, we have got to come up with a better term to describe these things! They already have enough of a hurdle to get over when trying to understand that “theory” doesn’t mean “guess” in a scientific setting, so I guess we can’t afford to confuse them by playing around with other words’ meanings.
    These processes were described as random to me, but also while teaching that something that is “random” within limits isn’t as random as the random that people associate with the word “random”.

    …I’ll stop saying that word now…

  5. 5 jaredcormier
    January 4, 2009 at 10:16 pm

    I never went anywhere, Stacy, I’m just busy reading tons of literature at the moment, I’ve been around, just not very active…

    Oh, and A.S., like I have said “reality doesn’t have to fit into language”

  6. January 4, 2009 at 10:18 pm

    “reality doesn’t have to fit into language”

    Good one. Tell that to a few philosophy students for me!

  7. 7 jaredcormier
    January 5, 2009 at 1:22 am

    I’m not trying to pick on philosophy students or philosophers, but they too frequently try to make everything fit into neat little boxes. The whole idea of Kuhn’s “scientific revolutions” makes me want to laugh/cry every time I hear it. There is no “scientific revolution” followed by a period of “normal science.” We get revolutionary tools which lead to new types of “normal science.” The whole thing is “normal science.”

    Example: Evolution wasn’t new at the time of Darwin (Lamark), it just didn’t have the valid mechanism which had been explored, we got one of the mechanisms and then, when genetics was discovered, we had a new tool which allowed us to discover so many more of those other neat little things that result in evolution. New tools are revolutionary, the science is the same.


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