How Evolution Causes an Increase in Information, Part II




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Published on Feb 28, 2007

In this video I introduce Information Theory and show how it can be applied to information storage in DNA. This video is a bit technical, but it is critical to understand these points to counter creationist ignorance. I have boiled it down as much as I can.

The second half of the video presents a study by Dr. Thomas Schneider, which was published in 2000 in Nucleic Acids Research. This study simulates a small genome containing a gene that codes for a DNA binding protein and a stretch of DNA containing 16 sites that if that protein binds to any of them the organism will gain a fitness advantage. The result of this simulation clearly shows that natural selection coupled with random mutations will lead to a steady increase in information over generations.

There is one interesting aspect of the study I could not fit into the video. As I mentioned, the binding sites are 6 nucleotides long and therefore can store up to 12 bits of information, but looking closely at the data you see that the information content plateaus at 4 bits (slide at 8 minutes). Why is this? Why doesn't the information content continue to increase past this point? Information Theory makes a clear prediction. Since there are 16 sites in a genome 256 nucleotides long, each site only needs to store 4 bits each to be recognized. To put it another way. If I wanted to specify one unique site out of 256 I would need 8 bits (log2(256) = 8) but if I wanted to specify 2 sites out of 256 it would be the same as specifying 1 site out of 128 so I would only need (log2(128) = 7) 7 bits. If we continue this, if I want to specify 16 sites out of 256 it is the same as 1 site out of 16 which requires (log2(16) = 4) 4 bits. The evolution does not proceed past 4 bits since it offers no further fitness advantage (4 bits is enough to make 0 mistakes). Now if the binding sites were restricted to only 2 nucleotides those would become fixed (2 nucleotides * 2 bits = 4 bits). Since it is restricted to 6 nucleotides the consensus is not as fixed (i.e. it is slightly degenerate). This matches exactly what is seen in nature when scientists look at the sequences of binding sites for proteins like transcription factors. So in short, Information Theory makes a prediction that is confirmed by the biology.

As I showed in my first video and reiterate here

Random Mutations + Natural Selection = Increase in Information

Many thanks to Dr. Schneider for performing the study that this video is based on.

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Learn the facts, spread the truth, and most importantly, Think About It.

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