Evolution: The Modern Synthesis

[L.A. Moran]

Many people do not understand current ideas about evolution. The following
is a brief summary of the modern consensus among evolutionary biologists.

THE MODERN SYNTHESIS
A Theory of the Mechanism of Evolution

The idea that life on Earth has evolved was widely discussed in Europe in
the late 1700's and the early part of the last century. In 1859 Charles
Darwin supplied a mechanism, namely natural selection, that could explain how
evolution occurs. Darwin's theory of natural selection helped to convince
most people that life has evolved and this point has not been seriously
challenged in the past one hundred years.

It is important to note that Darwin's book "The Origin of Species by Means
of Natural Selection" did two things. It summarized all of the evidence
in favor of the idea that all organisms have descended with modification
from a common ancestor and thus built a strong case for evolution. In addition
Darwin advocated natural selection as a mechanism of evolution. Biologists
no longer question whether evolutioon has occurred or is occurring. That
part of Darwin's book is now considered to be so overwhelmingly demonstrated
that is is often referred to as the FACT of evolution. However, the
MECHANISM of evolution is still debated.

We have learned much since Darwin's time and it is no longer appropriate
to claim that evolutionary biologists believe Darwin's theory of Natural
Selection. I can understand why this point may not be appreciated by the
average non-scientist but it is inexcusable that Creationists continue to
argue against ideas that are 130 years old.

The incorporation of genetics and population biology into studies of
evolution led to a Neo-Darwinian theory of evolution that recognized the
importance of mutation and variation within a population. Natural selection
then became a process that altered the frequency of genes in a population
and this defined evolution. Current ideas on evolution are usually referred
to as the Modern Synthesis which is described by Futuyma;

"The major tenets of the evolutionary synthesis, then, were
that populations contain genetic variation that arises by random
(ie. not adaptively directed) mutation and recombination; that
populations evolve by changes in gene frequency brought about
by random genetic drift, gene flow, and especially natural
selection; that most adaptive genetic variants have individually
slight phenotypic effects so that phenotypic changes are gradual
(although some alleles with discrete effects may be advantageous,
as in certain color polymorphisms); that diversification comes
about by speciation, which normally entails the gradual evolution
of reproductive isolation among populations; and that these
processes, continued for sufficiently long, give rise to changes
of such great magnitude as to warrent the designation of higher
taxonomic levels (genera, families, and so forth)."

Futuyma, D.J. in EVOLUTIONARY BIOLOGY
Sinauer Associates, 1986; p.12

This description would be incomprehensible to Darwin since he was unaware
of genes and genetic drift. The modern theory of the mechanism of evolution
differs from Darwinism in three important respects:

1) It recognizes several mechanisms of evolution in addition
to natural selection. One of these, random genetic drift,
may be as important as natural selection.

2) It recognizes that characteristics are inherited as discrete
entities called genes. Variation within a population is due
to the presence of multiple alleles of a gene.

3) It postulates that speciation is (usually) due to the gradual
accumulation of small genetic changes.

In other words, the Modern Synthesis is a theory about how evolution works
at the level of genes, phenotypes, and populations whereas Darwinism was
concerned mainly with organisms, speciation and individuals. This is a major
paradigm shift and those who fail to appreciate it find themselve out of
step with the thinking of evolutionary biologists. Many instances of such
confusion can be seen here in the newsgroups.

Laurence A. Moran (Larry)
Dept. of Biochemistry
University of Toronto

[Mike Phillips]

Thank you for you informative post(s). I have the same
understanding(s). I also agree that it is mis-understandings on both
sides of the debate which make the debate untenable. Many operate from a
definition of terms which is incomplete or erroneous. Mutation Theory,
Genetic Drift, Speciation, and Population Biology are excellent examples
of both the strengths and the failures of evolutionary theory. I wish
more people understood these things in forums such as these as well.
Most of the time, I see high school biology bilge gain strength from
sheer repetition, rather than from real data. Any effort to address
shortcomings, however, always appends a label to the poster(s) whether
deserved or not. It is because of these attitudes that the shortcomings
of evolutionary theory are seldom aired. Thanks for taking the time to
post.

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