From: William Pearson (wil.pearson@gmail.com)
Date: Thu Feb 23 2006 - 16:13:32 MST
On 23/02/06, Eliezer S. Yudkowsky <sentience@pobox.com> wrote:
> Alejandro Dubrovsky wrote:
> > On Thu, 2006-02-23 at 06:39 +0200, Mikko Särelä wrote:
> >
> >>Certainly, though we should probably not consider a gene to be one bit,
> >>but more like a software component. Still we get an upper limit on the
> >>complexity by considerint that the human genome has 3 billion DNA base
> >>pairs. Since there are four different possible base pairs that means 2
> >>bits of information giving us a maximum of 6 Gigabits ~ 700-800 Megabytes.
> >>
> >>And that is very much overestimated by assuming that each base pair
> >>actually codes useful information about brain structure. Overestimated for
> >>the reason that no one should be able to claim that the complexity is
> >>_higher_ than that. It is most certainly lower than that, probably on the
> >>order of at least two decades (which would place it at 7-8MB) [reason
> >>being at least 90% seems to be junk, not all genes code for brain
> >>structure, and we know that a base pair does not code for 2 bits of
> >>information (similarly claiming that a gene codes for only 1 bit of
> >>information, if two different alleles exists is false idea).
> >>
> >>Anything wrong with my analysis?
> >
> > Someone could claim that the optional methylation of the C base is
> > another state, ie each base pair having 5 options. Then you can
> > multiply by 3 to tell whether the stretch of DNA is in A-DNA, B-DNA or
> > Z-DNA form (obvious overestimation there since the stretches cannot be
> > one base long, and not all stretches can form Z-DNA). Then you can add 3
> > to that multiplier to tell whether the DNA is hanging loose, it's
> > wrapped around a histone, it's hanging between histones, or are more
> > tightly packed (the tightness of the packing depends on the acethylation
> > of the histones, but past some level of packing i'm assuming they are
> > just not read at all, so there's probably no need to make the multiplier
> > acethylation-level dependent) (again, gross overestimation since minimum
> > size for each of these stretches is >> 1) (also, add, not multiply to
> > the multiplier since these states afaik do not get a choice of whether
> > they are in A-,B- or Z-). That'd be 5 x 6 = 30 choices per base. So
> > that would be lg(30) x 3 billion about 15 billion bits, slightly under 2
> > gigabytes as upper limit.
>
> Heh. Unfortunately, this potential extra data storage buys you nothing
> whatsoever in the way of information.
>
> Natural selection pressure on mammals maxes out at O(1) bits (of Shannon
> information) per generation. See
> http://dspace.dial.pipex.com/jcollie/sle/, though the argument is older
> than that - it appears for example in George Williams's "Adaptation and
> Natural Selection".
>
> Bases mutate at a rate of 1e-8 per base per generation.
> Thus natural selection cannot maintain more than 1e8 bits of information
> against the pressure of degenerative mutation.
This assumes that what is important over evolutionary time scales is
important for creating an individual or for an individuals function.
For example the cone snail has a higher than average rate of mutation
in regions of the genome that encode for the toxins*. This implies
that over evolutionary time it doesn't matter so much what the base
pairs are. They hold little information that would be useful for
future generations.
So lets say we found a shorter way of representing one of these myriad
toxins, would we expect a genetically altered cone snail with this
gene rather than the longer gene to become more dominant due to
increased efficiency of copying of the genome (less base pairs less
energy needed to copy it). Probably not because as the shorter length
genome became dominant it would become something that would be adapted
to by the snails prey and because it doesn't have the storage to store
the random variations it would not be able to create the new toxins.
Because while it doesn't matter exactly which toxin it is, it matters
that it is different from the rest of the population. And so you need
the storage in the genome to store the difference.
So rather than the bit being stored as a single base pair it is stored
in the choice between a long sequence of base pairs and the mechanisms
for increasing mutation in that area and a more shorter but more
static genome.
Will Pearson
Or google for cone snail toxin mutation for more information
Also see the book Darwin in the Genome
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