> No, of course there's no way to prove that natural selection &co are
> responsible for common ancestry, or that Pluto really has an orbit, or
> a multitude of other things. The approach scientific theories usually
> take, though, is to figure that if the mechanisms we see now are sufficient
> to explain history, and there is evidence that they were operational, then
> that is the scientifically defensible theory.
>
And my only point is that scientists have not proven that natural
selection acting on random variations are sufficient to explain
macroevolution -- even though it does appear through observation to be
sufficient for microevolution.
> But there is still a bit of vagueness in the definitions
Boy, is there!
> --that is, by
> 'microevolution' you seem to agree that natural selection is responsible
> for the sorts of variations we can see happening now. This includes
> speciation events, BTW. I agree that there are open questions surrounding
> how natural selection could operate to drive common ancestry, and its
> role in this process is under current discussion (as Al mentioned in another
> post in this thread). That is, what are the developmental parameters
> which constrain selection? Why is the rate of 'macroevolution' so low
> in comparison to the rate of 'microevolution'? Where are sticking points
> that make overall geologic-time evolution so slow? These sorts of questions
> are very much relevant, and I think there is enough reason for people to
> be cautious about attributing it all to natural selection. But common
> ancestry (what is typically called 'evolution' popularly) is a fairly
> different animal from these considerations, and is supported on different
> grounds.
>
The problem is in your parenthetical statement, "what is typically called
'evolution' popularly." I am not concerned as much with how biologists
define evolution as I am with how evolution is defined "popularly."
The NABT defines evolution this way:
The diversity of life on earth is the outcome of evolution: an
unpredictable and natural process of temporal descent with genetic
modification that is affected by natural selection, chance, historical
contingencies and changing environments.
(Their definition used to include the terms "impersonal" and "undirected"
along with "unpredictable" and "natural", but they agreed to remove it
earlier this year, much to the chagrin of several noted scientists.)
Certainly, this implies your "descent from common ancestry" definition.
However, it implies your definition not only at the microevolutionary
level, where it has been observed, but also at the macroevolutionary
level, where it has not been observed.
The new handbook from the NAS, "Teaching About Evolution and the Nature of
Science" spends more time defining "theory" and "fact" than it does
evolution. But in Chapter 5 of that book, it does have this to say:
What is evolution?
Evolution in the broadest sense explains that what we see today is
different from what existed in the past. Galaxies, stars, the solar
system, and earth have changed through time, and so has life on earth.
Biological evolution concerns changes in living things during the
history of life on earth. It explains that living things share common
ancestors. Over time, evolutionary change gives rise to new species.
Darwin called this process "descent with modification," and it remains a
good definition of biological evolution today.
Again, "descent from common ancestors", and again, no distinction between
micro and macro.
Look at this discussion in the same handbook, just a bit further down on
the page from the previous one:
Is evolution a fact or a theory?
...
Scientists most often use the word "fact" to describe an observation.
But scientists can also use fact to mean something that has been tested
or observed so many times that there is no longer a compelling reason to
keep testing or looking for examples. The occurrence of evolution in
this sense is a fact. Scientists no longer question whether descent with
modification occurred because the evidence supporting the idea is so
strong.
Macroevolution has never been observed or tested. Therefore, it is not a
fact. But the NAS argues otherwise.
> > > Paleontological discoveries of the
> > > time frames in which the various species existed, transitional fossils, and
> > > so on are all supporting lines of evidence for this conclusion.
> >
> > Perhaps, but they are at best circumstantial evidence. I could conceive
> > of a creationist theory that also accounted for not only the existence of
> > these fossils (whether or not they are truly transitional is always open
> > to debate), but for the absence of other fossils. So, where would that
> > leave us?
>
> It leaves us nowhere until you actually do.
>
Unfortunately, you are right. Unfortunate, because I shouldn't have to
propose a counter theory in order to challenge a current theory. What you
are saying, in essence, is that science can not stand the answer, "I don't
know." If evolution is the "best" theory available (notice I said "if";
I don't really think it is) even though there is not enough evidence to
support it, are we forced to accept it as true? Does science
abhor a vacuum, too? If you don't have enough evidence to support a
theory, can't you say, "I don't know?"
> > > The worry about 'fact' and 'theory' is usually a misnomer: any scientific
> > > idea is 'theoretical' in the sense that further observations can overturn
> > > or modify it. Some are so well grounded, though, that they serve further
> > > investigations in the role of 'facts.'
> > >
> >
> > Not "any" scientific idea, but EVERY scientific idea! But if that is
> > true, why do scientists such as Gould speak of "the fact of evolution" as
> > if no further observations could overturn it?
>
> Because they're talking about common ancestry, which is the material with
> which they work. That the Solar System actually exists, and is not painted
> with a brush on some sky-roof every evening, is a theory astronomers have
> which they would probably call a 'fact,' and which underpins their
> investigations into what the solar system is like. Common ancestry is
> the 'fact' which underpins modern evolutionary investigation into the
> processes that drive evolution and the paths it has taken.
You should be able to predict what I'm going to say next: Common ancestry
may (MAY!!) be a fact of microevolution, but it is far from a fact of
macroevolution. But Gould et al do not make that distinction.
> > The worry about 'fact' and 'theory' is a real problem, not just a semantic
> > one. The concern is that treating evolution as a 'fact' leads scientists
> > to make assumptions, and that taints their research. Not that assumptions
> > aren't necessary, but you have to be willing to follow the findings of
> > your research to their conclusion, wherever that might be. If you are
> > already convinced that evolution is a 'fact' and simply must have
> > occurred, you may be reluctant to follow your own research to its
> > logical conclusion.
>
> If you do not think that common ancestry is a fact, then modern evolutionary
> theory cannot be of much interest to you, since it is attempting to explain
> something which you don't believe exists.
That's my point. Common ancestry IS NOT a fact. It is a theory.
If you DO think that common ancestry is a fact -- if you no longer
challenge it as a theory -- then what happens? Suppose you found evidence
that contradicted the common ancestry theory. What then?
Niles Eldredge himself once claimed that paleontologists who had found
fossils that didn't seem to support the currently accepted theory of
evolution were considered "failures, and, more often than not, weren't
even published." That's one of the things that can happen when you start
treating a theory as a fact, which the NABT and NAS seem to encourage.
> Just like astronomers still are not trying to convince
> people that telescopes actually record real things when pointed at the
> heavens, and are not instruments of evil, biologists are, for the most
> part, uninterested in rehashing the settled arguments of the past.
>
Oh, come on! Are you equating astronomy with evolution? At least I can
SEE the stars, whether they are real or painted on. None of us have seen
or can ever hope to have seen the Great Common Ancestor To Whom We All
Owe Our Lives. One is based on direct observation. The other is based on
inferences made from 500 million year old fossils.
My only point through this whole discussion has been that a distinction
needs to be made between microevolution and macroevolution. One is an
observable fact, the other is a mere theory -- at best.
And why shouldn't a distinction be made? Must the same mechanisms acting
at the micro level also be responsible for macroevolution? Sub-atomic
particles disobey the laws of gravity in favor of atomic forces.
Have you ever studied economics? No, you haven't. You have studied
either microeconomics (economics at the individual or household level) or
macroeconomics (economics at the group, societal or governmental level)
or both. Microeconomic theory is almost worthless at the macro level, and
vice-versa. What's more, there are several competing macroeconomic
theories (classical, Keynesian, etc.). All I'm saying is, the same is
true for theories regarding the origin of life.
Erich Hurst
Houston, Tx