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Asked by ssuewing to Tom, Rachael, Penny, Jennifer, Jean-Paul, Dave on 10 Jan 2014.
Question: I have recently been reading that scientists are now saying that random mutation would statistically not be able to produce the amazing complexity we see in the natural world. It has been compared to monkeys writing Shakespeare. What are the current scientific ideas that explain this? Is it something to do with the Hox genes that were mentioned?
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David Christensen answered on 10 Jan 2014:
I hadn’t heard this before and it doesn’t seem to make sense to me. Unless we can first see a mechanism by which mutations happen non-randomly, then I think we have to assume they happened randomly. Life has evolved over some 4 billion years, all over the world, with crazy huge numbers of cell divisions happening every second for most of that time. I don’t know if scientists have a number for how often a mutation arises in a cell, so I don’t know how they could work out how long a series of mutations to drive evolution this far would take in their statistical model of life. We haven’t had infinite time for evolution to progress this far, but it’s 4 billion years is still a huge amount of time and the numbers of organisms that have been alive is also surely enormous. So, if an infinite number of monkeys could theoretically write all of Shakespeare in an infinite amount of time, then why couldn’t evolution progress as far as it has given a near infinite amount of time and a near infinite number of organisms lives.
Anyway, if there are scientists that think that completely random mutations are not enough, then presumably the mutations would have to arise specifically to try to make evolution happen faster. This would mean that mutations would have to happen more when the organism needed to adapt because of pressure in its environment or from a predator. I can see that maybe stresses might make mutations happen more, so this could be a way to increase the speed of evolution, but this is still quite random. Even if the rate of mutations increases, I can’t see how the mutations could happen totally non-randomly (i.e. actually choose which gene to mutate to help the organism). And the tendency for mutations to happen faster during stress would be a characteristic that developed through random evolution. Therefore the ability to evolve faster through faster random mutation would have evolved through random slow evolution. On top of that, evolution would make sure than any animal that had mutations happening too fast would likely die out because those mutations would be more likely to cause damage rather than help adaptation.
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Penelope Mason answered on 10 Jan 2014:
Hi, this is pretty interesting. I’m not sure what you are referencing, either, so forgive me if I am off the point, but I think perhaps what this sounds like is that our complexity has now been found to come from more layers than previously thought. In other words, although mutation at the DNA level drives change and speciation, these changes are also subtly (and not so subtly) tweaked by various further layers of regulation.
Even at the basic level, changing one thing i.e. having one mutation cause a difference in one protein, does not happen in an isolated way, but forms part of a highly connected and complicated (and fluid) milieu of proteins each doing different things, often with layers of redundancy. Therefore correlating the direct outcome on the protein to the outcome on the organism can be quite difficult. Then there are further layers…
For example, epigenetic marking of the DNA will change the way the mutations are expressed, and this can be modulated by the environment, and may be transmitted to further generations (although unlike permanent DNA mutation this does not persist for ever).
As you mentioned, HOX (homeobox) genes are involved similarly in regulation. They code for proteins that bind to enhancer sites at the beginning of other genes and modulate how they are turned on and off. There are many HOX proteins, and they all bind very similar codes of DNA, hence a mutation in this binding sequence (for either the HOX protein or the gene it targets) can give a multitude of effects, depending upon what the change is and how much of a difference it makes.
Other regulators of gene expression are being discovered all the time that can fine-tune how mutations are expressed – for example, small RNA fragments have been shown to be involved in regulation and silencing of the DNA message (which is itself RNA – DNA [the blueprint] makes RNA [the moveable working plans i.e. the message] makes proteins [the product]).
Finally, the environment itself, for example the availability of nutrition can also modulate the end result of how genetic mutations express in a population, a rather simple e.g. being lack of food causing stunting in one particular population.
The bottom line is that it just isn’t as simple as DNA mutation makes different protein causes specific change – there are many other factors that modulate how this happens, so statistically calculating for just the direct effect of mutation (admittedly the direct gross driver of evolutionary complexity) misses out these other factors that are more subtle.
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Rachael Inglis answered on 10 Jan 2014:
Just to add, that although there are many layers of complexity underlying the range of plants, animals, etc we see in the natural world, comparing it to monkeys writing Shakespeare might not be as silly as it sounds, if you think about the way that evolution works.
Sure, it seems highly unlikely that if you give a monkey a pen and paper, that it will write a comedic/tragic play in Olde English. But evolution doesn’t work by going from nothing to something very complex in a single step– a bacterium is not going to get a single mutation that makes it become an elephant. Evolution has produced the vast range of complex life we see around us because when a mutation occurs that helps an organism to survive or gives it some advantage over other organisms, this mutation is selected and gets passed on to the next generation. Every time this happens, it may only be a very slight advantage, but it has happened countless times. Evolution is a gradual process, but the important thing is that the organisms keep getting better because the mutations that have a positive effect will be kept. Now, if we go back to our monkey with the pen and paper, we could say that every time it makes a scribble that looks like a letter in the alphabet, then that’s an ‘advantageous mutation’, so we could ‘select’ that scribble. If the scribble that looks like a letter is used as the starting point for the next scribble, then very gradually, over time, we could get a word, then sentences, paragraphs, and so on. Fortunately for us, evolution has had the best part of 4 billion years!
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Dave commented on :
The way that the comparison with the monkeys writing Shakespeare doesn’t make sense is that evolution isn’t directed with a goal in mind. We know what a Shakespeare play looks like because we’ve read them, so we can look at what the monkeys write and say, “That isn’t Shakespeare. Try again.” Evolution doesn’t know that it is trying to make an elephant and nobody is checking that it has done the right thing. Evolution is producing new organisms more like if we asked the monkeys to produce a script for a new play. Then we would look at what they write and say, “Hmmm, I’m not sure I like the ending. Why did the main character have to die? Do you think you could work on it a bit more, please?” The script would evolve and change over time.
Unfortunately this analogy breaks down here as well. Presumably that script would eventually be put on the stage as a play or it would be made into a film. At that point the script has reached an end point where it will never be changed again. It may not be perfect, but it will not evolve further. In contrast, evolution in nature never stops. There is no perfect (or imperfect) end point to an elephant. As long as there is competition and there are pressures on survival of elephants, they will be changing and evolving gradually.
Andrew commented on :
Great question – you may be interested by an experiment that Bob MacCallum and Armand Leroi from Imperial College London have done called Darwin Tunes. It’s a bit like the monkeys producing Shakespeare idea. In Darwin Tunes they started with a random music generator. It generated short loops of music to be selected by a volunteers (acting as the environment). The highest rated loops (the fittest) would reproduce and their characteristics would be passed to the next generation of musical loops. Over time a complex and quite beautiful music evolved. The key to this is that in each generation information was passed down, just like with our genes, so the random music generator wasn’t producing the complex music from scratch. Inheritance is key. Also, and like Dave says about the play, the music at the end wasn’t planned. Though it is nice (in my opinion), Bob and Armand didn’t try to make that exact composition.
Anyway, take a look – it’s a fascinating experiment and one of those fun and clever ideas in science. Their website is http://darwintunes.org/ but visit https://soundcloud.com/uncoolbob/darwintunes-the-first-7200 to listen to the actually music over each generation.