I am hard put to find truly unique distinguishing processes in macro v micro evolution.
MICROEVOLUTION AND MACROEVOLUTION ARE GOVERNED BY THE
SAME PROCESSES
Michael R. Dietrich
Department of Biological Sciences
Dartmouth College
When Theodosius Dobzhansky discussed the distinction between micro
and macroevolution in his landmark book, Genetics and the Origin of Species
(1937), he accepted that evolution below and above the species level could be
distinguished, but that they were not produced by fundamentally different
processes. In doing so, Dobzhansky advocated a theory of evolution unified at
different levels by common processes, most notably gradual change over time
shaped by natural selection (Dobzhansky 1937, Smocovitis 1994, Provine 1988).
Dobzhanksy’s unification was quickly pulled into controversy as Richard
Goldschmidt argued for a “bridgeless gap” between micro and macroevolution
(Goldschmidt 1940). Today the divide between micro and macroevolution still
exists, but not as Goldschmidt imagined it. Most scientists would accept that
there are distinct phenomena that can be categorized as microevolutionary and
macroevolutionary. Patterns of variation within a species are classic examples of microevolutionary phenomena, while patterns of phyletic change associated
with either punctuated equilibrium or mass extinction are recognized as
examples of macroevolutionary phenomena. The question, however, is whether
there are also distinct processes that underlie these phenomena. Dobzhansky’s
answer and the answer from the evolutionary synthesis was that there is not.
In this essay, I will review the historic controversy over the distinction
between micro and macroevolution in order to clarify the terms of the dispute. I
will then turn to contemporary arguments for macroevolutionary processes.
Rather than cast this debate in strongly polarized terms that simply deny that
distinct macroevolutionary processes exist or could exist, I will reframe the
debate in terms of the relative significance of distinct micro and
macroevolutionary processes. I will argue that microevolutionary processes are
much more significant than uniquely macroevolutionary processes....