[...]
> > 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.
No argument there. Most (all?) experts in the field (my impression is) do
not think NS explains evolution completely. This is the hobby horse
of someone as prominent as Gould, for example, and there are many, many
others.
[...]
> > 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.)
Sounds good to me.
> 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.
Of course not, no-one was around. :-)
> 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.
That's right. As I said above, arguments for common ancestry in general
(as the process by which life got to the place it is now) are quite
different from arguments about selection and the role it plays. There
are places where selective influences seem fairly important, and many
where they are hard or impossible to pin down with any certainty. (That's
probably why the statement you quoted before says evolution is just
partly affected by selection, there are many other factors.)
> 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.
No, common ancestry *is* observed. There are enough lines of evidence
to make it basically unimpeachable. The question now is *how*.
> > > 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?"
Science says 'I don't know' about practically everything. I mentioned
above that the majority of the time, we simply have no idea for why
evolution took the course it did. This will probably always be true
for individual cases, no matter how much knowledge accumulates about
general tendencies, overall effects, and so forth.
Besides being more than willing to say "I don't know," scientists are
also eager to try to explain, which leads to multitudes of candidate
theories being proposed for phenomena, often in the face of very little
evidence. When one has survived lots of tests (like heliocentrism), it
is considered profitable to build on it instead of rehashing it. For
one thing, it is incredibly boring to keep doing the same thing forever!
> > 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.
Whaaaa.... I'm lost here. I thought we had agreed that 'macroevolution'
*was* 'common ancestry.'
> > 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?
I don't think you understand yet, despite reading all about the
distinction in whatever textbook it was. :-) There is no National Academy
of Facts which votes in scientific fact and allows people to work on
theories based on them, and hunts down and persecutes scientists who
don't. There is just a lack of interest in rehashing it. This can
lead to some outcomes: one is that the program goes nowhere, in which
case the supposed "fact" becomes suspect (but usually not renounced
until an alternative theory comes along). Or, it can progress, the
theories based on the "fact" can be productive, yielding more insights
into the nature of the "fact" and further confirming it, and it can
become embedded tightly enough into the framework of science to make
its absolute rejection fairly unthinkable (although of course revisions
are always possible). There are many, many examples of both kinds
of programs about. If you think common ancestry is troubled and needs
to be thrown out, then it is up to you to explain why.
> 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.
Gould, at least, has some rather pointed comments about the wattage of
people who make him out to look like a Creationist. I can't imagine
Eldredge would think much differently. You are aware, aren't you, that
both of them are firmly behind common ancestry, and are of the opinion
simply that they have a new way of explaining that; that is, they are
involved in the modern pursuit of explanations *for* common descent,
and not defenses *of* it?
> > 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.
I can't imagine you aren't aware that the proposition is that the
stars are much older than that...
> 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.
I'd understand you much better if you'd use more conventional terms,
but your objection to common ancestry is noted.
> 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.
Leaving aside the bit about gravity (you understand the business about
orders of magnitude, right?), there is no necessity that the mechanisms
we observe today are responsible for common ancestry. If they are
*sufficient* to account for it, and we never find evidence that something
else interfered, then that will probably always be the scientifically
defensible position. Of course, showing they are sufficient is a
fairly involved process, and is the fodder for the current debate. None
of this (it would seem) has much bearing on either the 'fact' of
common ancestry or those about selection and other evolutionary forces
acting in the world today.
> 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.
It appears you aren't up on your economics, either.
-Greg