Re: Challenge for Darwinists - Protein Synthesis
- From: "Iain" <iain_inkster@xxxxxxxxxxx>
- Date: 16 Jul 2006 03:41:54 -0700
Wall Of Sleep wrote:
Richard Forrest wrote:
Wall Of Sleep wrote:
allanm wrote:
Wall Of Sleep wrote:
allanm wrote:
Wall Of Sleep wrote:
<snip>
Statistically, all variation in an initially varying population will be
eliminated (in the absence of mutation) in (4 * population size)
generations.
So looked at either way - the origin of a sequence or the fate of
variants in a derived population - the existence and persistence of
variation proves the historic reality of ongoing mutation.
It would seem to me that the forces of nature are working against random
mutation at every turn then. I'm still totally unconvinced that this
vehicle can be the driving force behind the millions of unique
biological systems we see today.
<snip>
I'm afraid you've missed my point then. What I described is not a
preservative force but part of the inexorable force for *change*. You
assume that mutants will *always* be eliminated. But they have (at
least) the same chance as every other allele of becoming the 'norm'
as variants are lost.
Consider this:
A population of just 4 individuals. A single diploid gene. Lets label
each gene individually, one from each parent:
Aa
Bb
Cc
Dd
If each different gene were a different variant, we would, by the
inexorable loss of variation I described, end up with all A, or all a,
or all B...... etc etc. Each ancestral gene has an exactly equal chance
of becoming the 'norm', and the other 7 will go. The existence of
variants is thus evidence of the historic action of mutation in
*opposition* to the tendency to homogenize.
Lets then take a theoretical future homogeneous population resulting
from this effect - all A, say.
A neutral mutation arises , A*. It too has an exactly equal chance of
becoming the 'norm' further down the line. So 1 in 8 random neutral
mutations will become 'fixed' - the population becomes all A*.
Then from that position, 1 in 8 times, a further mutation, A**, becomes
fixed..... How does a population manage to stay the same against this
backdrop of mutation and elimination of 'competing' variation?
And this is without any natural selection. Stick that in the picture
and we have a means by which a mutational change can buck the stats. It
no longer has to make do with an equal chance. Selection can work both
ways, of course. Good ideas get a bunk up. But equally, bad ones get
their chance knocked below equality - a preservative force, against
change but also against deterioration. (And, this slightly ups the
chances for the other variants that are 'better').
Multiply this argument up over the whole genome, factor in the
continual variation of the fitness 'landscape' due to external
factors, and you may (I hope) see that the combination of mutation,
statistical factors and selection renders stasis highly unlikely. Or at
the least, get some flavour why people who work in this field don't
seem to share your misgivings.
The problem with this scenario is that it doesn't work! Dog breeders
have been using artificial selection for hundreds of years now and have
never come up with anything that can be called a new species.
Try getting a Great Dane and a Chiwawah to breed.
Are you suggesting they are different species?
No; I think he is suggesting that if they were the only two breeds of
dog, they would become two species as the generations go by, because
they would never breed.
The present gene flow between chiwawahs and great danes is via other
extant breeds. If that passage is sethered by geography or environment,
you have a recipe for speciation. Even now, the flow is pretty weak.
However, I think his main aim was to emphasise that there can be more
than one cause of reproductive isolation -- for example, physical
difficulties in mating.
In fact, the inability of chiwawahs and great danes to breed comes
close to the "ring species" idea (but not quite). A ring species is a
rare population of organisms that varies gradually along a big
geographical stretch. An organism from one end, and an organism from
the other end, are effectively different species from one another, but
every organism in the population is able to mate with its neighbour
nonetheless. If we imagine for a moment that all of your ancestors and
all of a chimpanzee's ancestors were still alive, and they were
arranged in a geographical ring, in order of kinship, humans and
chimpanzees could be said to belong to the same ring species.
The most intense experiments were done with Drosophila and nothing
viable came of their efforts - certainly nothing that resembled a new
species. After thousands and thousands of generations, with intense
mutation inducers, all they came up with were - Drosophila.
Except where they have, of course.
http://www.pnas.org/cgi/content/abstract/101/33/12232
"We suggest that duplicated genes that have yet to evolve a stable
function at the time of speciation may be candidates for "speciation
genes," which is broadly defined as genes that contribute to
differential adaptation between species."
Notice the "may be". I see no real substance here.
Of course there is substance.
"In the best-known organisms, like Drosophila, innumerable mutants are
known. If we were able to combine a thousand or more of such mutants in
a single individual, this still would have no resemblance whatsoever to
any type known as a [new] species in nature." Richard B. Goldschmidt,
"Evolution, As Viewed by One Geneticist," American Scientist, January
1952, p. 94.
Wow! A reference from 54 years ago!
Of course, no work has been done in the field of genetics since then.
Or has it?
"Most mutants which arise in any organism are more or less
disadvantageous to their possessors. The classical mutants obtained in
Drosophila usually show deterioration, breakdown, or disappearance of
some organs. Mutants are known which diminish the quantity or destroy
the pigment in the eyes, and in the body reduce the wings, eyes,
bristles, legs. Many mutants are, in fact lethal to their possessors.
Mutants which equal the normal fly in vigor are a minority, and mutants
that would make a major improvement of the normal organization in the
normal environments are unknown." Theodosius Dobzhansky, Evolution,
Genetics, and Man (1955), p. 105.
Getting closer. This is only 51 years old. Hell, I was born by then!
Evidently they weren't aware of the paper published in 2004 which
showed them wrong.
How silly of them.
Mind you, perhaps it's this other 2004 paper they didn't know about:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15304653&dopt=Citation
Same as above paper?
Or this 2001 paper:
http://www.pnas.org/cgi/content/abstract/98/23/13195
"Substantial genetic differentiation, as great as among species, exists
between populations of Drosophila melanogaster inhabiting opposite
slopes of a small canyon. Previous work has shown that prezygotic sexual
isolation and numerous differences in stress-related phenotypes have
evolved between D. melanogaster populations in "Evolution Canyon,"
Israel, in which slopes 100-400 m apart differ dramatically in aridity,
solar radiation, and associated vegetation. Because the canyon's width
is well within flies' dispersal capabilities, we examined genetic
changes associated with local adaptation and incipient speciation in the
absence of geographical isolation. Here we report remarkable genetic
differentiation of microsatellites and divergence in the regulatory
region of hsp70Ba which encodes the major inducible heat shock protein
of Drosophila, in the two populations. Additionally, an analysis of
microsatellites suggests a limited exchange of migrants and lack of
recent population bottlenecks. We hypothesize that adaptation to the
contrasting microclimates overwhelms gene flow and is responsible for
the genetic and phenotypic divergence between the populations."
I noticed no mention of any attempts to breed the two "species" to see
if their resultant offspring would be fertile. Which brings me to this:
what definition of "species" are they using? Is it the broad definition
of "differences", or is it the classic definition of "able to produce
fertile offspring"?
Or this 1993 paper:
http://links.jstor.org/sici?sici=0014-3820(199304)47%3A2%3C432%3AFSIDPA%3E2.0.CO%3B2-L
Could not access this one.
Or even this 1982 paper:
http://links.jstor.org/sici?sici=0014-3820(198201)36%3A1%3C132%3AMEFISI%3E2.0.CO%3B2-1
Or this one either.
Or this 1995 paper:
http://www.pnas.org/cgi/content/abstract/92/7/2519
"It is generally believed that Drosophila melanogaster has no closely
related species with which it can produce the viable and fertile hybrids
that are essential for the genetic analysis of speciation. Following the
recent report of molecular differentiation between a Zimbabwe, Africa,
population and two United States populations, we provide evidence that
strong sexual isolation exists between the D. melanogaster population in
Zimbabwe and populations of other continents. In the presence of males
of their own kind, females from most isofemale lines of Zimbabwe would
not mate with males from elsewhere; the reciprocal mating is also
significantly reduced, but to a lesser degree. The genes for sexual
behaviors are apparently polymorphic in Zimbabwe and postmating
reproductive isolation between this and other populations has not yet
evolved. Whole chromosome substitutions indicate significant genetic
contributions to male mating success by both major autosomes, whereas
the X chromosome effect is too weak to measure. In addition, the
relative mating success between hybrid and pure line males supports the
interpretation of strong female choice. These observations suggest that
we are seeing the early stages of speciation in this group and that it
is driven by sexual selection. The genetic and molecular tractability of
D. melanogaster offers great promise for the detailed analysis of this
apparent case of incipient speciation."
Note "would not mate" is not "can not mate" or more importantly "cannot
produce fertile offspring" - hence the conclusion that this might be
"the early stages of speciation", rather than real speciation. These
are real desperate attempts to find speciation IMO.
Shades of grey -- There are varying liklihoods of successful
reproduction.
Are you claiming that speciation is unobserved???
~Iain
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