Re: A question of timing


Mr. Nuwer:

I will try to answer your question "So I am wondering what it is about
Darwinian evolution that_requires_a long and gradual process." If you
are looking for a more scientitic answers maybe one of the few
biologists on s.b.e. will answer. An alternative is to take courses in
biology.


The reason Darwinian evolution in general is gradual is due to phyletic
gradualism and a example is given of the eye which is a complex
adaptation. There also may be room for what is called punctuated
equilibriumism but this only occurs in small isolated populations in
peripatric speciation. Punctuated equilibrium is only fast in
geological time. The author states, "
"What is rapid? 10,000 - 100,000 years can be an instant in geological
time (especially in the context of some deposition rates) but is ample
time for evolutionary events in populations. Recall that the shift from
the peppered to the dark form of Biston betularia occured within the
span of 100 years by a completely "Darwinian" mechanism.

Also, one has to consider the species and its environment. There are
those who will argue there have been many adaptations of sharks over
the millions of years (and there have been) but their "basic plan"
doesn't seem to have changed much. If that is not a good example one
can take the Duckbill Platypus which has not changed signifigantly in
millions of years. The point is there are organisms which have been
around far longer than humans (such as bacteria) and several of them
haven't evolutionarily changed much in millions of years and long
before Homo Sapiens which certainly evolved over time more. There are
creatures which have been around longer than Homo Sapiens and haven't
evolved hardly compared to newcomer Homo Sapiens on the evolutionary
scene. So its a combination of the particular organism and its
environment which effects Darwinian evolutionary changes or speciation.
In fact, despite all the speciation changes we've made over millions of
years I think Homo Sapiens are no longer adaptable to their
environment. So although I know Darwinian evolution is scientifically
proven I think it will be necessary for man to intervene in Darwinian
evolution and through possible advances in germline genetic engineering
tailor our genome to where it is adaptable to its environment.
Unfortunately, it won't possibly come soon enough to prevent living
nightmares to many children and women. The four horsemen are still in
the DNA charriot.

Another example of graduality in Darwinian evolution is "stasis".
Stasis means good Darwinian evolution it it selects the stronger over
the weaker. Or, the weak, diseased and stupid are selected against
while those who are healthy, strong and intelligent survive and
reproduce. This has been somewhat weakened due to modern "civilization"
but the underlying mechanism operates. By those standards one might
think Darwinian evolution is good and some would like to take away
civilization's constraints and alllow it totally unimpeded. Remember,
however, what I stated about Darwinian evolution. In a nutshell, I
think it is incompatible with modern civilization. This is not a new
concept by any means. Freud, Hawking and others. So I think the
following statement I found is true, " If stasis is due to
developmental constraints then there is an interesting "battle" going
on between the environment and the homeostasis of the organism. When I
read that it hit me in the gut.



Michael Ragland










The punctuation debated focused a lot of interest on the notion of
hierarchical phenomena (sensu units of selection). One important
hierarchical issue is Species Selection: differential rates of increase
or decrease in species diversity among different lineages due to
differences in rates of speciation and/or extinction. The basic
principles of species selection are 1) speciation is random with
respect to phenotype, 2) most changes occur at speciation, 3) different
extinction and speciation rates are due to some biological properties
of the different taxa.


Some consequences: 1) species selection can introduce evolutionary
trends and 2) differences in morphological or taxonomic rates of
evolution among different lineages can be due to species selection. The
important point is that it is the pattern of speciation that drives
such trends, not the direction of morphological changes.


An excellent example of the dynamics of species selection (or how one
might interpret data from the fossil record in light of differences in
extinction and speciation rates) is provided by Hansen's studies of
planktotrophic vs. non-planktotrophic gastropod (snails).
Planktotrophic lineages last longer in the fossil record (lower
extinction rate) See fig. 23.3, page 643. However, the proportion of
planktotrophs decreases in the fossil record (see figure 23.4, page 645
and note typo in figure caption). How can one account for this apparent
paradox? If one invokes a higher speciation rate among
non-planktotrophs, then this might do it; i.e., species selection might
account for the patterns of diversity changes. Read the text for this
section (pp. 641-644).


A general question about species selection: is it a pattern or a
process? Following the parsimony of G. C. Williams, can we explain
species selection by differential survival of individuals within
populations, and if so is species selection just a by-product of
individual selection., or do higher level processes operate? (thus the
hierarchical issue in species selection). If the latter is true, the
big question remains: is macroevolution decoupled from microevolution??
(i.e., are population-level processes insufficient to account for
evolution above the species level? If you talk to a population
geneticist they would say NO! If you talk to a paleontologist some
would say OBVIOUSLY!


.

Relevant Pages

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