Re: Does Larry Moran concede that macroevolution breaks down to manysteps of microevolution?

rev.goetz wrote:

Larry Moran wrote:

On 25 Apr 2006 06:07:01 -0700, rev.goetz <jimgoetz316@xxxxxxxxx> wrote:

Moran has not responded to my reply post within a week. Could this
suggest that Moran concedes that macroevolution breaks down to many
steps of microevolution?

[snip]


I will work with your definition of population genetics and focus on
microevolution. And I hope that we agree that microevolution includes
natural selection, apart from cases of drift. Is that correct?

I define microevolution as the changes in alleles frequencies within
a population. Thsose changes are mostly due to natural seleciton and
random genetic drift.

Do you agree with that definition?


I think you limit your definition of "microevolution" to a minimal
definition of population genetics. I believe that the most common
definition of microevolution is "evolution within a species." And
microevolution includes the following: changes in allele frequencies
within a population, changes in breeding population sizes, branching of
subpopulations, adaptations and variation within a species.

In the case of changes in breeding population sizes, studies of genetic
diversity can detect population bottle necks and expansions in a
particular lineage. So population genetics includes the study of
changes in breeding population sizes.

I don't think so. The most common definition, or at least the one that I
know, is what Larry said. I don't know of anyone who thinks that changes
in population size should be called evolution. There's no reason why
everything you can study using genetic diversity assays should be called
evolution. And of course adaptation and variation within a species is
change in allele frequency.

Natural selection is from the outside of biological populations and
includes all physical environmental phenomena that influence
populations. And natural selection can change allele frequencies and
cause population sizes to increase or decrease. And in many cases,
decreases in population sizes result in terminal extinction.
Additionally, changes of population sizes and allele frequencies in
turn change the direction of natural selection.

This is very confusing. Are you saying that things like climate change
are part of micorevolution?

Yes, but you must understand that I include adaptation within a species
as part of microevolution.

So does everyone. But we shouldn't confuse evolution with the
environmental factors that influence evolution. Climate change isn't
evolution, and I don't know anyone who thinks it is. But climate change
might cause evolution. Wet roads aren't car accidents either.

And any study of adaptation is incomplete if
it does not include known information of environmental issues that
influenced adaptation. And many adaptation studies include speculation
of environmental issues that influence adaptation. And the term
"adaptation" implies that a population is adapting to its
environment. So we cannot study adaptation while ignoring the
environment that influences the selection of an adaptation. On the
other hand, environmental issues influencing selection can be viewed as
background factors to adaptive evolution within a species.

Just because the study of X includes Y, that doesn't mean that Y is X.
Bad reasoning. If you study a car accident, the wet roads will very
likely go into your report.

All phenomena of macroevolution such as terminal extinction and species
competition and the branching of populations occur in small scale
within microevolution.

Hmmm ... I'm having trouble with that one too. If the eruption of a
volcano wipes out a species how does that fit into the definition
of microevolution?

That is a good point. Terminal extinction is the end of evolution for a
particular population or sometimes several populations. We must
remember that my definition of microevolution includes changes in
breeding population sizes. Your example of a volcano wiping out a
species could be an example of natural selection against a population
to the point of the breeding population size decreasing to zero.

That's not natural selection. Extinction isn't natural selection.
Natural selection requires that there be differential reproductive
success based on genetically-based phenotypic differences. If the
population is wiped out there was no differential success. If, somehow,
the characteristics of that population made it less likely to survive an
eruption than another population also in the path of the eruption,
that's species selection. Which is macroevolution.

And changes in breeding population size aren't evolution, much less
macroevolution.

If we could hypothetically read a hypothetical
year-by-year study of all biological lineages over the past four
billion years, then we would see that all macroevolution would be
broken down into steps of microevolution.

That's possible. By tracing the lineage of an existing species back
through time we can see that most of the changes seem to be the product
of lots of microevolution. This works for humans, for example.

However, as soon as we add in anther species, say chimpanzees, we get
into trouble. It's hard to explain the splitting of the lineage using
only microevolution.

My hypothetical year-by-year study of biological lineages over the past
four billion years also applies to human-chimp divergence. For example,
the last common ancestral population of humans and chimps divided into
subpopulations. There may have been gene flow between the
subpopulations for thousands of years, but eventually the lineages
became isolated from each other, perhaps due the exploration of
ecological niches. Eventually, each lineage had evolved to the point
where hybrids between the lineages were infertile. At this point, we
could say that cladogenesis had occurred. And a year-by-year study of
the evolution in the two lineages from subpopulations to cladogenesis
would show many steps of microevolution that added up to
macroevolution. And we could continue this study to evaluate the
adaptive radiation of hominids. And we would see that all hominid
evolution within the last 6-10 million years could be broken down to
many steps of microevolution.

Larry's point is that if microevolution is evolution within a species,
then speciation can't be microevolution, because it can only be
understood in the context of two species, or of what becomes two
species. Sure, each population is undergoing microevolution. But you can
only understand the process with reference to both.

When we add in Neanderthals and all of the other
hominids that went extinct it gets even more complicated. How do we
explain why some species survived and others didn't if we can only
rely on population genetics?


As I have suggested above, we should not divorce population genetics
from natural selection (apart from cases of drift). And all hominid
species that faced terminal extinction may have faced a change of
environment that selected against their populations.

Nobody is suggesting that natural selection be divorced from population
genetics. But natural selection involves individuals, not populations.
Selection against populations isn't natural selection. It's species
selection. The allele frequency of a population that's going extinct may
change, or it may not. There may be some differential reproductive
success, or there may not.

It's not very satisfactory to just say that all of their allele
frequencies dropped to zero. That kind of explanation seems to lack
something.


We could say the following:

Macroevolution involves the origin of species and higher taxa during
evolutionary periods of hundreds or thousands or millions of years. And
macroevolution sometimes focuses on grand-scale phenomena such as mass
terminal extinctions and species competition that change the long-term
dynamics of microevolution.

Macroevolution is an historical field of study. It's goal is to determine
the particular history of life on this planet. In order to do that it
relies on much more than population genetics.

Yes, both microevolution and macroevolution should not divorce
population genetics from natural selection (apart from cases of drift).

Since nobody does that, it's unclear what you are trying to say.

.

Relevant Pages

  • Re: Macroevolution FAQ 2.1D
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  • Re: Macroevolution FAQ 2.1D
    ... > Macroevolution - its definition, ... > "microevolution" is, and by this they seem to mean that whatever evolution is ... > evolutionary change at or above the level of species. ...
    (talk.origins)
  • Re: Behe in the latest Protein Science
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  • Re: Why is it macroevolution?
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  • Re: Why is it macroevolution?
    ... population - level processes, or it is defined as only changes in ... leaves much left over to be macroevolution. ... species' range shrinks. ... Then the change in B is anagenesis, or microevolution. ...
    (talk.origins)
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