"Macroevolution" from Re: P.Johnson on James Dobson

David Campbell (bivalve@mailserv0.isis.unc.edu)
Thu, 18 Nov 1999 09:28:18 -0500

>We may have a problem of definitions here. If you consider _change over
>time_ evidence for macro-evolution, then you are right. But I doubt if you
>use "change over time" as your definition of macroevolution, do you?

Macroevolution has become popular among those rejecting common descent as a
term for "the biological evolution I do not believe in". In
paleontological use, it is generally used to refer to biological
evolutionary processes active at or above the species level, especially any
that are different from ordinary population-level biological evolution.

>In short, common descent has some evidentiary support at lower
>taxonomic levels but is not supported by evidence at the higher taxonomic
>levels, i.e., macroevolution.

Except for paleontology and molecular systematics. There are at least
transitional fossils between many classes, orders, family, genera, and
species; depending on the definition of phyla, some forms may be
transitional between them. Molecular and subcellular strucutural
similarities point to universal common ancestry.

>Thirdly, if you consider the concept of _natural selection_ as the heart of
>the Darwinian theory, as I do, then you will have many disagreements. The
>oldest one is Mivart's objection (called Mivart's Dilemma) stated as,
>"Natural selection is incompetent to account for incipient stages of useful
>structures."
[useful details snipped]
>The problem for macroevolutionists is to employ natural selection to account
>for "incipient structures", for example, between the mammalian land ancestor
>to the "useful structures" of modern blue whales.

Natural selection does not try to account for incipient structures (except
in the case of exaptation, the use of a structure that evolved for some
other purpose). It assumes variation exists and proceeds from there.
Incipient structures are explained by mutation.

Natural selection is also not the only selective force. Genetic drift,
catastrophes, sexual selection, and various genetic effects also must be
taken into account.

David C.