Re: How can the evolutionary progress from slime to humans be linear?

"Perplexed in Peoria" <jimmenegay@xxxxxxxxxxxxx> wrote in
news:dnsufj$14ad$1@xxxxxxxxxxxxxxxxxxx:

>
> "William Morse" <wdmorse@xxxxxxxxxxxx> wrote in message
> news:dnoion$2463$1@xxxxxxxxxxxxxxxxxxxxxx
>> The size of genome does reflect a complexity difference between
>> prokaryotes and eukaryotes, although within each of these two groups
>> your statement may be correct.
>
> I've seen the claim that that there was a second quantum jump in
> genomic size in the "progression" from invertebrates to vertebrates.
> But, with those two exceptions, there doesn't seem to be much
> correlation between genome size and "progress".
>
>> I doubt that I could prove it, but I would bet that the size of the
>> genome in eukaryotes would as a general rule reflect the length of
>> time from the development of eukaryotes to the organism's birth.
>> This argument follows Gould's drunkard's walk idea, that there is a
>> steady increase in "complexity" simply because the low side of
>> complexity is fixed at 0 while the high side is infinite.
>
> Your drunkard's walk analogy is interesting. But it is important to
> realize that (particularly if the drunk is constrained to a single
> dimension) the probability of a step toward the origin is the same
> as the probability of a step away from the origin. So our drunken
> genome shrinks over time as often as it grows.

Yes the probability of a step toward the origin is the same as the
probability of a step away from the origin. But as the number of steps
taken increases, the lower bound of the minimum value of the steps is
fixed at 0 while the upper bound of the maximum value of the steps will
increase (asymptotically) without limit. So our drunken genome grows more
often than it shrinks, albeit only slowly.



>> Ignoring true "complexity" -
>> however we define that - and looking simply at size of the genome, it
>> would seem that absent mechanisms that severely limit the size of the
>> genome, there should be a steady increase over time in genome size.
>
> Not clear to me. And there are some clear exceptions. Fugu, for
> example. Possibly yeast. And I don't think that you can rule out the
> possibility that reptiles, birds, and mammals have smaller genomes
> than the ancestral amphibians.

I thought I had made clear, but obviously did not, that I was not arguing
for an inexorable increase in genome size over time. So clear exceptions
to a general trend don't really affect the argument. But I certainly
agree that if there are mechanisms that consistently (I should not have
said severely) limit the size of the genome, then my argument will not
hold.

The real problem with my argument is that it is not really testable, at
least until we figure out a way to measure the size of the genomes of 500
million year old organisms.

Yours,

Bill Morse

.

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