Backing Up Evolution

By Darcy Cowan 02/11/2009 6

I’ve said it before and no doubt I’ll say it again but we know science works because it makes predictions that we can then measure against the universe and determine if the models we have created to describe it are accurate or not. One of the more successful models is the theory of evolution by natural selection. A criticism levelled against the theory of evolution by detractors is the claim that new information can not be introduced into the system, only taken away. This is actually false but lets consider how we might tackle this question scientifically

First, the underlying assumption here isn’t unreasonable, let’s explore it. The accepted mechanism of introducing change in an organism, change that natural selection can then act upon, is mutation. Mutations involve a mistake in the copying of an organism’s DNA, this might consist of a change in a single base of a gene (an insertion of an extra base, deletion of an existing base or swapping one base for another) or it might involve large stretches of DNA. The basic principle that is relevant here is the same, a change is made to the blueprints of life in our cells.

As you might expect there are many more ways of being wrong than there are of being right, any random change is more likely to introduce a defect in the complicated machinery of life than it is to create an improvement (bearing in mind that “improvement” is a value judgement that really cannot be applied here but don’t focus on the wrong part of the story). So on the surface it would seem that random change is very definitely a bad thing, mutations would likely lead to loss of gene function, and by extension, loss of information and specifically death of the individual.

How might evolution get around such a problem? One solution would be to make copies of critical genes, this way is one copy is damaged through mutation the other can still function and produce a viable organism. The “spare” gene would then be free to mutate and the resulting gene may be selected for or against by natural selection (or human breeders).

If you have been reading closely you will have picked up on our prediction, the genomes of organisms should contain copies of various genes that allow mutations to occur without harming the individual that accumulates them. It turns out this is exactly what we find.  A recent study found a significant amount of redundancy in the genome of Zebrafish which allows mutations to occur in genes critical to development without lethal consequences to the fish.

The researchers intentionally gave mutagens to populations of Zebrafish and looked for changes in fish morphology indicative of mutations. In particular they created a mutation that lead to the loss of most of the fish’s scales, similar to that of Mirror Carp. The mutation was traced to a gene critical to normal development, further investigation revealed that the gene existed as a redundant pair, only one of which being required for normal development.

It is tempting to talk about this phenomenon in terms of intention, the gene was duplicated so that it could mutate and provide raw material for evolution. This is a mistake however, evolution can not move towards any putative desired future state. the genes that are duplicated in this way will be random and the mutations that affect the genes will be equally random, there are likely many genes in the Zebrafish that are not duplicated and would cause death to the individual if they were to change. This does not detract from the fact that a proposed mechanism for introducing new information into an organisms genome has proven correct.

Science is Awesome.

Posted in Religion, Sciblogs, Science Tagged: genetics, natural selection, Religion, Research, Science, selection

6 Responses to “Backing Up Evolution”

  • Damn Darcy, you really know how to make a guy wish he had enough time to write about these things!

    One of the nicest examples of gene duplication in evolution is the RNASE1 genes of leaf eating monkeys. A gene duplication allowed selection to fine tune one RNASE1 enzyme for the acidic conditions in the gut (caused by the leaf eating behaviour) while keeping the “original” functionality in place. Environmental change -> gene duplication -> selection -> new information!

    There was a really nice paper (summarised here) a while back that looked at a bunch of fungal genomes and made some generalisation about how duplicate genes evolved – in short lots of changes in regulation and added complexity in networks less completely new biochemistry.

  • I’ll take that as a complement, thanks.
    This was one of the more interesting pieces I came across this week. The intersection of scientific knowledge and ideologies is fascinating I find, and a great opportunity for communication as well.

    Great papers, thanks, I’ll have to make time to peruse them properly.

  • Duplication and divergence is a major theme. I can remember reading bioinformatics papers written from (now) about 30 years ago on this issue! (I read them some time ago, but not 30 years ago.)

    As David was pointing out, one increasing theme being observed is that the coding regions themselves often don’t change that much, so much as the regulatory regions around them alter, so that essentially the same gene (and it’s products) is put to a new use through new regulatory control.

    (This is the sort of thing I’m “supposed” to be posting, but I never seem to get around to it… Nice to see your post.)

  • True Grant, this stuff isn’t exactly new and yet the same old arguments from deniers keep coming up. Still it’s good to have recent concrete example to point to when they do.

    Changes in regulatory sequences are amazing, minor differences can have such dramatic effects it belies the simple “Informational” argument of creationists.

  • 30 years? Try Ohno (1970) Evolution by Gene Duplication for the first manifesto . At the turn of the 20th centurly people were talking about chromosomal duplication driving diversification and even though Darwin wasn’t talking about genes when he said this in The Origin there is some similar thinking going on:

    We have formerly seen that parts many times repeated are eminently liable to vary in number and structure; consequently it is quite probable that natural selection, during the long-continued course of modification, should have seized on a certain number of the primordially similar elements, many times repeated, and have adapted them to the most diverse purposes.

  • I said “about”, David. I’m not keen on academic pissing competitions either 😉

    I was thinking my Ph.D. supervisor’s work, e.g.

    Repeating sequences and gene duplication in proteins.
    McLachlan AD.
    J Mol Biol. 1972 Mar 14;64(2):417-37.

    I think you know I was referring to molecular sequence data 😉 I’m aware of the chromosome duplication story, although it’s just general background knowledge to me, not something I dig into.