On Mon, 2 Feb 2004 07:03:10 +0000 (UTC), 
Jim Menegay  wrote:
> lamoran{at}bioinfo.med.utoronto.ca (Larry Moran) wrote in message 
> news:...

[snip]

>> Please give me a precise definition of evolution that works and is a 
>> "creature of theory." 
> 
> "Evolution is change in gene frequencies caused by differential survival
> and reproduction of organisms."  This definition is a creature
> of the neo-Darwinist theory (Fisher, Wright, et al.)  It certainly 
> wasn't Darwin's precise definition - he had never heard of genes.  His
> definition involved things like speciation and adaptation, even though
> his causal ideas were not that different from Fisher's.  People between 
> Darwin and Fischer (Bateson, for example) also talked about evolution
> without necessarily talking about changes in gene frequencies.

Thank-you very much for offering a concrete example that we can
examine. The definition of evolution that I prefer is the one in the
article that I wrote for the Talk.Origins Archive. I don't claim that
this definition is original. In that article I've tried to summarize
the consensus among evolutionary biologists.

http://www.talkorigins.org/faqs/evolution-definition.html

  "Evolution is a process that results in heritable changes in a 
   population spread over many generations."

There are many variations of this definition. Some of them are mentioned
in the article. The most common variant refers to changes in the 
frequency of alleles in a population.

Keep in mind that this is a minimal definition of evolution and doesn't
address the birth and extinction of populations. It is, admittedly, a
creature of prior knowledge in that it assumes an understanding of 
populations of organisms and of heredity. 

What are the possible causes of these changes that would form part
of evolutionary theory? One of them is a Lamarckian form of evolution
where the heritable characteristics of a population changed within an
individual in response to the environment. In theory, we could imagine
that there would be no differential survival of organisms in this
this type of evolution (i.e. every individual gave rise to one and 
only one descendant). The heritable characteristics of the population
would change over time and the population would evolve.

We know that this isn't the way that evolution occurs but it isn't ruled
out by the definition of evolution. That's the way it should be.

What are some other possible causes of changes in heritable characteristics?
One of them is mutation. New alleles (mutations) arise in a population
at measurable frequency. This is an important part of evolutionary theory
and it is consistent with the definition of evolution since the definition
doesn't specify causes. Your definition does specify a cause. It says ...

   "Evolution is change in gene frequencies caused by differential 
    survival and reproduction of organisms."  

Is it your intention to eliminate mutation and possible Lamarckian
explanations by defining them out of existence? Why do you want to do 
this? 

I realize that we're quibbling over details. Perhaps it would be best
to think of your proposed definition as a simple variant of what most
of us agree is the standard definition. I really don't see that it's
profoundly different in spite of the fact that I think it's a bit too
restrictive.

> Since Kimura and Hamilton, we have better precise definitions that work
> even better.  That is because we have better theories.  Of course, if
> you prefer to think of precise theories as not containing any reference
> to causation, then Kimura and Hamilton don't change Fisher's precise
> definition, in your view.  But you have to admit that the definition of
> evolution HAS changed since Darwin.  And, for that matter, the definition
> of "gene" has changed since Fisher.

I don't see that Kimura and Hamilton had any effect on the definition
of evolution. I also don't see any significant different between the
definition that I prefer and what Darwin thought of as the minimal
definition of evolution. Darwin didn't know as much as we know about
genes and how they work but he did know about heritable characteristics
and why they were important in evolution. In fact, he proposed a theory
of genes.

>> Please explain why your "precise" definitions isn't 
>> mentioned in the textbooks on evolutionary biology. 
> 
> Clearly, it IS mentioned in textbooks.

Okay. Let's assume that your proposed definition is mentioned in textbooks.
Why is it more "precise" than the one I prefer? Is it simply because
you use the word "genes" instead of "alleles" or
"heritable"? Or, is
it because you specify a cause, a cause which seems pretty nebulous to me.

>> I'm sure you must have such a "precise" definition in
mind because if 
>> you don't your posting doesn't make sense. It would be a great help to 
>> me if someone could come up with an example definition instead of making 
>> vague accusations against the standard one. (I'm expecting a comparision 
>> between your precise definition of evolution and the
"loose" one that 
>> evolutionary biologists use. Which one is better, in your opinion, and 
>> why?)
> 
> The precise definition is best for explaining, testing, and understanding
> the theory.  The loose definition is best for expanding, improving, and
> overthrowing the theory.

Evolutionary theory is supposed to explain the causes of evolution. In
order to do this we have to have a common understanding of what evolution
is. That's the purpose of a definition. There may be many possible causes
of evolution. Some of them will be right and some of them will be wrong.
It seems to me that you are advocating that we change the definition of
evolution according to the best available evolutionary theory of the day.
If we had done this in the past then the definition of evolution might
include a cause such as natural selection and that would be extremely
self-serving and wrong. It would restrict evolution to only those causes
that most people accepted in any given year and eliminate by fiat all
competing causal theories. 

There are some people who would like to do this. They would like to 
"define" evolution as changes caused by natural selection and eliminate
random genetic drift as completely irrelevant to evolution. Some of these
same people want to rule out neutral changes. They don't think they
represent real evolution. In my opinion this is a serious error.

> Personally, I am disappointed that the modern precise definitions of 
> evolution don't explicitly mention speciation.  

This is a problem. If we want to cover all levels of evolution then
we should also deal with the birth and death of populations. That's
why I emphasize that the definition is a "minimal" definition designed
to distinguish between processes that resemble evolution at the population
level and process that really count as evolution.

>> > I encourage doubters to produce a list of phenomena and check this
>> > conceptual framework against their list.  My list included the origin
>> > of life, the origin of the moon, human monogamy, photosynthesis, and 
>> > others.  In each case, I notice that the competing theories (that I am
>> > aware of) agree on a loose definition of the phenomenon, but introduce
>> > more or less subtle differences in their precise definitions.
 Particularly
>> > interesting to Einstein fans is one of Larry's examples - gravity.
>> 
>> I don't understand these sentences. Could you elaborate? Are you referring
>> to *definitions* of "the origin of life" etc. I would
*define* "the origin
>> of life" as "the point in time when the first life
began." Do you have 
>> something else in mind?
> 
> I would change your loose definition to "the process by which the
first life
> began" for starters.  The process is what people are interested in.  But 
> then someone is going to ask for a definition of "life". 
And people like 
> Francis Crick are going to foul things up by offering theories like 
> "Directed Panspermia".  Should we ask for the origin of life on Earth?
> People like Cairns-Smith are going to come up with theories of organisms 
> built from clay that are ancestral to modern organisms only with some 
> stretching of concepts.  Every theory forces some revamping of any attempted
> precise definition.

Please offer a definition that illustrates the problem and how you would 
solve it.

> You really never understand exactly what it is you are trying to explain
> until you explain it!  Thereby, you produce a precise definition.  But
> even before you succeed, you had a goal in mind for what you were going
> to explain - that vague goal is the loose definition.

Hmmmm ... I really don't see your point. The distinction between what
you call a "loose" definition of evolution and a
"precise" definition
of evolution is very close to nitpicking. Nitpicking can be fun but
there's a risk that we miss the main point.

>> What about "gravity"? The word is normally *defined* as
something like 
>> "the attractive force between massive bodies that is
proportional to the 
>> product of their masses and inversely proportional to the square of their 
>> separation." This doesn't look to me like a definition that's
a creature
>> of theory. What did you mean?
> 
> Actually you are giving Newton's precise definition of *gravitation*, not
> of gravity. Gravity is the force here on earth that makes apples fall and
> it was known long before Newton.  

I think this discussion is getting way too semantic for my liking.

> Galileo provided the first quantitative theory of gravity. Newton reduced 
> gravity to a special case of a new theory - gravitation. Einstein showed 
> that Newton's gravitation, along with the laws of conservation of momentum 
> and energy, are only approximations to a more general theory - General 
> Relativity.  The loose definition of gravity as a tendency of things to 
> seek the center of the earth is still valid, but the precise definition 
> changes with each new theory. Even if you leave out Einstein, gravity now 
> includes a mix of the centripetal force due to gravitation, the centrifugal 
> force due to the earth's rotation, and small changes in the shape of the 
> earth caused by lunar and solar tides.
> 
> Incidentally, Newton had a loose definition of gravitation before he had
> a precise one.  He knew there was an attractive force from Copernicus,
> but it took a careful analysis of Kepler's laws to determine that it must
> be an inverse square force.

Please give me your preferred *definition* of gravity so I can try and 
see what you're talking about. It seems to me that you are confused about
the difference between a definition of gravity and the cause (explanation)
of gravity.



Larry Moran
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