Abstract
A recurring debate in evolutionary biology is over the extent to which
microevolutionary processes operating within species can be extrapolated to
explain macroevolutionary differences among species and higher taxa (36,
38, 45, 46, 53, 67, 68, 80). As discussed by Stebbins & Ayala (83), several
issues involved must be carefully distinguished, such as (a) whether micro-
evolutionary processes (e.g. mutation, chromosomal change, genetic drift,
natural selection) have operated throughout the history of life (presumably
they have); (b) whether such known processes can by themselves account for
macroevolutionary phenomena; and (c) whether these processes can predict
macroevolutionary trends and patterns. In another, phylogenetic sense, macroevolution is ineluctably an extrapolation of microevolution: Organisms
have parents, who in turn had parents, and so on back through time. Thus, the
branches in macroevolutionary trees have a substructure that consists of
smaller branches and twigs, ultimately resolved as generation-to-generation
pedigrees (Figure 1). It is through these pedigrees that genes have been
transmitted, tracing the stream of heredity that is phylogeny.
It would seem that considerations of phylogeny and heredity should provide
a logical starting point for attempts to understand any connections of
macroevolution to microevolution. Yet amazingly, the discipline traditionally
associated with heredity and microevolutionary process (population genetics)
developed and has remained largely separate from those fields associated with
phylogeny and macroevolution (systematics and paleontology). Thus, several
classic textbooks in population genetics (35, 39, 64) do not so much as index
"phylogeny," "systematics," or "speciation," while the equally important
textbooks in systematics (55, 81, 96) can be read and understood with only
the most rudimentary knowledge of Mendelian and population genetics.
Notwithstanding some evidence for recent increased communication between
these disciplines (40, 71), too many systematists and population geneticists
continue to operate in largely separate realms, employing different languages
and concepts to address issues that should be of importance to all.
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