Re: Defining&testing "macroevolution" (was: Testing the Laws of Intelligence)

From: "mel turner" <mtur...@xxxxxxxxxxxxxxxxxxxxxxx>
As for its meaning, "microevolutionary" seems pretty clear to me:
having to do with microevolution, in other words having to do with
evolution of populations below the level of speciation.
And what is *that* supposed to mean?
From: "mel turner" <mtur...@xxxxxxxxxxxxxxxxxxxxxxx>
It means that changes within a population or within one species is
called "microevolution",

Is that a reductionist definition (plural of "changes" merely means
that it applies to each change individually), or is that a gestalt
definition (plural of "changes" means that a whole ensemble of
changes together may constitute a single application of the
definition)?

Is it even meaningful to speak of a single population over a long
span of time? If a1 begats a2 begats a3 begats ... begats a5000,
can we say that a1 and a5000 and everything between are necessarily
each a member of the *same* population? I don't think so. Do you?

I would perhaps agree that a1 and a2 are necessarily in the same
population. Hence any evolution that occurs from a1 to a2 must be
"microevolution" per your definition. The same logic applies to
each link a[n]->a[n+1] in the chain. But if "same population" isn't
a transitive relation, it's possible that the end-to-end comparison
a1 to a5000 isn't microevolution because it connects two
individuals not in the same population. From that point of view,
macroevolution is nothing more than a sufficiently long chain of
microevolution links such that end-to-end transitivity of "same
population" fails.

But another way to look at this is to say that every time the most
trivial change happens in statistics, such as a single birth or
death, the population isn't exactly the same as it was before, it's
now a different population from what it was before. Evolution
defined as change in population statistics happens every time such
an event changes the population (except in a population o identical
clones). But per that definition, there is no such thing as
"changes within a population", it's always change from one
population to a new slightly-different population.

I think that covers the version of definition using the word
"population". Either the definition is meaningless (every single
event of evolution is from one population to another), or "same"
isn't transitive and you're just playing a game of words as to
where end-to-end transitivity breaks down.

As for the version with the word "species", we have another
problem. Species isn't a well defined product except at a single
moment of time or over a short interval of time when it's actually
possible in theory to conduct breeding experiments (or observe
presence/absence of natural breeding). It's an arbitrary
nomeclature decision whether we use the same name for successive
begatted populations over a million years or whether we chop up
that span of time into sub-spans where we use different species
names over different sub-spans of time. And with other definitions
of "species", it's even more arbitrary what different populations
are considered to be the same species.

If it's not well defined which two populations are the same species
and which are different species, then we can't reasonably define
something as "microevolution" depending on whether it's from one
species to the same species. It's just a stupid word game.

as opposed to the origin of new species

Like I've said several times, there's no thing as a new species,
except in rare cases where chromosomes are suddenly duplicated en
masse, and even then a lot of times the event merely duplicates the
same event that occurred elsewhere previously thereby
re-establishing an old species again. Except for genome-duplication
events, every species is merely a slight modification of an old
species that existed just previously. Homo sapiens wasn't a new
species, it was merely (initially) a slight modification of Homo
erectus or somesuch, and (later) a slight modification of "itself"
(not really itself except with the word-game trick of calling a
whole succession of species as if they were *the*same*).

and groups of related species from a common ancestral species,
which evolutionary biologists have termed "macroevolution".

I call that "common descent", which is simply a topological
description of the way the "tree of life" branches over time. If
you follow from the trunk out to any single branch, there's no
macroevolution, merely a long chain of microevolution. It's only
when you compare two different branches, and notice how they *were*
a single branch but *are* now two separate branches that we observe
"common descent" and you call it "macroevolution".

As I understand it, a single branch-splitting (species-splitting,
"speciation") "event" is actually a gradual process, whereby two
sub-populations gradually develop reproductive isolation via
decreased survival of cross-breeds, whereby gene flow between the
two populations gradually declines to zero.

If you look at one tiny portion of that species-splitting process,
like when crossbreed success decreases from 80% (relative to
monobreed success) to 79%, does anybody refer to that tiny decrease
as "macroevoution"? If not, but if the entire process from start to
end (100% to 0%) *is* called "macroevolution", then once again it's
nothing except a failure of transitivity of "same", a word game. If
you want you can consider it an emergent property of studying whole
evolutionary trees as opposed to studying single reproductive
events.

It's a matter of scale and convenience, not necessarily any claim
that there must be any different processes involved.

Yes, except for sudden duplication of whole genomes that
immediately produces a reproductive barrier, we're talking about
nothing but large numbers of microevolution events.

I've often stated here that even the grandest-scale
"macroevolution" is merely accumulated "microevolution",

Yes, along a single lineage end-to-end from LUCA to leaf.

plus the cumulative effects of speciations,

Yes, when studying more than one lineage together.

plus the cumulative effects of extinctions of many of the resulting lineages,

Hmm, funny that extinctions are considered to be macroevolution.

over longe[r] periods of time.

Yeah. Given that it usually takes quite a long time just to run a
single species-split event all the way from start to end, you just
gotta have a longer spam of time if you want an example where the
distinction really "makes a difference".

(split long article here, more later)

.

Relevant Pages

  • Re: Behe in the latest Protein Science
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  • Re: My definition of microevolution is now posted
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  • Re: Macroevolution FAQ 2.1D
    ... Macroevolution - its definition, philosophy and history ... "microevolution" is, and by this they seem to mean that whatever evolution is ... evolutionary change at or above the level of species. ...
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  • Re: Macroevolution FAQ 2.1D
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