Loren writes: [...]
>>1) Mechanisms above the species level:
>>--------------------------------------
>>1a) Speciation. When a species population splits into two or more
>>reproductively isolated groups, and both groups survive and drift apart
>>genetically, the total number of different genes in the environment
>>increases.
Art, you responded:[...]
>Are you suggesting that a subset has more information that a set? I do not
>understand your argument here. If I choose two subsets from a set, how do
>the two sets have more information that the original set? IF two parents
>have ten children, do the ten children contain more information than the
>parents?
Loren's example initially caused me to do a second take too. But then
I re-read that section and realized that he was talking about groups that
split _and_ diversified genetically. Substituting "genes" for "alleles"
in Loren's letter, one can make a case that information has changed in some
way. I agree that one could score the change as positive or negative,
depending on the particular case and context. But all other things being
equal, I certainly think increased allelic diversity does correlate with
increased "information content".
> I would like you to quantify your illustration with some concrete
>examples where these kinds of measurements have been done. Unless you can
>cite specific examples that show DNA with more information in the offspring
>than in the parents, you are just arm-waving. The same result could be
>obtained by a decrease in information in one or both groups.
I haven't heard too many people dispute that many of the drosophila species
on the Hawaiian islands diverged from a smaller number (perhaps one?) of
founder species. They certainly do appear to have diversified significantly.
> Likewise the
>same results could be obtained with no increase in information if genes
>already present in the parent, but not expressed began to be expressed.
>Unless you can show your results are neither of the above, you have not
>demonstrated an increase in information, just a change in expression.
>The same criteria should be applied to all examples.
Ok, here's where I definitely part ways with you, Art. Let's say I've got
some plasmids (carrying a gene for antibiotic resistance) in a eppendorf
tube on my bench, right next to a test tube of E. coli to which I've
just added 200 ug/ml of ampicillin. I'll call that "case 1: soon-to-be-dead-
bacteria". In "case 2: happy, growing bacteria", I've got the same strain
of E. coli in the same tube but this time the plasmids are _inside_ the
bacteria and are expressing say, beta-lactamase. Would you say that the
"information content" is the same in both cases? I wouldn't, at least not
from a biological perspective. That's because biological information is
_context dependent_. For example, the "information" contained in the
plasmid sequence may add little to my eukaryotic cells (little more than
"food", that is), but it may make a big difference in the functioning of
a bacterium. Even Spetner does not deny that horizontal transfer can
increase the "information content" of an organism's genome.
But let's take your example, cryptic genes. What exactly is the information
content of an unexpressed, unused sequence of DNA? How does that compare to
one which encodes and expresses a functional protein? Remember that most
of the bacteria that started in these experiments _were not_ able to
benefit from their possession of these cryptic genes -- Most simply died.
So, I'd say that something changed when a mutation turned the gene back on.
And if that mutation was actually useful to the survival of organism,
then I'd score that as an increase in functional information, because many
of the cells which lacked that information did not survive the selection.
For those cells, that extra bit of DNA did as much good as a few nanograms
of resistance-encoding plasmids tucked away in my freezer would do for an
antibiotic-sensitive bacterium.
The same applies to changes in the expression of genes. Some "information"
must have been changed ("added" in the case of cryptic genes) for those
genes to express differently. Further, let's not downplay what goes on to
activate the expression of genes (as naive molecular biologists and sequence
jockeys tend to do). The combined mechanisms behind gene expression comprise
a massively interrelated, information processing system.
Now I'll agree that there is something which may distinguish a long, random
stretch of DNA from a gene which might encode a functional protein but which
has had its promotor damaged or which has taken a few mutations that dropped
a stop codon in the wrong place (Provided the damaged gene is also found
_inside_ an organism and in the appropriate context). So I can see that
the "information" one would have to add to either sequence and restore
expression of a particular function (the one lost by mutation) would be
different in each case. But either way, information must be added.
Aside:
Speaking of cryptic genes -- I wonder when the one required for vitamin-C
biosythesis in humans will turn on again. Odd, isn't it, that these
same pseudogenes are also found in higher primates that likewise share
our inability to survive without dietary supplements of vit-C? Perhaps
we haven't yet lost all the genetic "information" which shows we're related
to the primates.
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com (despam address before use)