The teaching of evolution

Stuart G. Poss Stuart.Poss at USM.EDU
Sat Oct 9 10:10:25 CDT 1999

Ed Pirog wrote:

> Stuart,
>         As an educator I hope you will not mind giving me just one testable
> experiment in macro evolution to support the theory of evolution.
>         Please try to understand my point. There should be just as much right to
> teach evolution as there is to teach creationism. After all, these are both
> just ideas. One more plausible than the other but still concepts just the same.
> Ed


I suggest that you avail yourself to the work of Peter Grant and subsequent
associates who have worked at a small isolated island in the Galapagos on the
evolution of beak size in galapagos finches.  To my knowledge this is currently one
of the best supported experiments showing  "macro-evolution" on an time scale
directly observable by humans.   I do not have the references to the original
papers, but I doubt these would be too difficult to find, given all the general
references to these experiments, which  contain numerous measures of beak lengths
between the large and small beaked individuals on these islands and its
correlations to seasonal changes in seed size on these islands.  These effects
result directly from the differential efficiencies and energetics among individuals
with different beak sizes.  Although the flucuations in actual lengths are
relatively small between generations, they are directly observable and the results
are as predicted by Darwin's theory.  There is of course, nothing in the theory
that would suggest that these need to large over a single generation as to be
conveneient for us to observe, but it is not hard to calculate that if seasonal
shifts over a number of seasons were always in the same direction, perhaps with a
drying of the climate favoring the production of relatively large seeds by plants
on the island, then the actual magnitude of beak size changes will be rather large,
in fact larger than seen among some of the many species of finches on the islands.

One must keep in mind that the evolutionary theory does not require that the
macro-changes take place all at once, simply for the convenience of human
observers.   Also these experiments are difficult to perform, except in isolated
areas, where one can eliminate or "control" the potential for other factors, such
as gene flow from neighboring birds,  that could in principle confound the
experiment.  There was a nice recent show on PBS narrated by Alan Alda discussing
this that could be shown to kids so that they could see the actual birds involved.

There are a host of other such changes that might be a little less "macro" than one
might like to demonstrate to students, but they do provide excellent observable
evidence of selection on traits in action.  A nice recent example is beak color
selection in zebra finches and its relation to deposition of testosterone in eggs
by females and its role in offspring survival (see the most recent Science
286(5437):126-128).   Interestingly, in this case it is evident that there is
differential modulation of selection on a measurable physiological trait between
the sexes. This is a relatively simple experiment and it would not be too difficult
to repeat on other birds, perhaps even in a classroom setting.  However, I suggest
for classroom use, you consider looking at insect systems for similar effects, as
these would likely be less costly and easier to maintain, although you will
probably need a microscope to take your measurements.  The classic studies of moth
coloration and its relation to predation and air pollution in the English
countryside are another easily understood example.

In most of these cases the exact molecular mechanisms at the level of which genes
are involved (ie functional genomics) are not yet known.  However, there are
investigators working on related problems and it might not be too long before a
fuller picture materializes for both features.  With a bit of patience and
attention to detail, we are already begining to see an amazing increase in our
understanding of Hox genes.  These genes form a family of genes that encode for
body organization in higher metazoans, including vertebrates.  Already, it is
extraordinarily difficult to image how such genes are not only seen among organisms
as seemingly dissimilar as Drosophila melanogaster, Branchiostoma lanceolatum, and
Homo sapiens, but have exact identity over much of their domains and evidently act
in exact or nearly exact functional homology relative to other genes in the hox
family UNLESS they evolved by means of natural selection.

Perhaps some of our other colleages can fill in the details with respect to these
particular cases and perhaps identify other better examples for you.  I have
limited knowledge of botanical experimentation in this area.

Whatever experiments you choose to highlight to your students, keep in mind that
that not all concepts or ideas are ammenable to scientific analysis.  To say they
are just ideas and somehow they are therefore equal is to misunderstand what
scientists do, when they do science.  Yes, they are concepts, but some concepts
have no observable basis in the natural world.  The equation 2=3 is a good example.
  The number of angels capable dancing on the head of a pin is also another of many
other kinds of concepts that  fall outside the realm of science, although at one
time important to mystics in India in explaining concepts important to them.  While
both are perfectly good concepts, neither has any observable meaning in the natural
world.  For concepts to be useful to scientists one must be able to study
properties of these concepts that can lead to their understanding and basis in
reality (the natural world).  Understanding can not be done in science without the
ability to observe, formulate testable and observable consequences that derive from
"experiments", and observe the outcomes of these "experiments".

The theory of evolution by means of natural selection is a scientific concept.  It
has has both observable consequence in the natural world and the potential to be
disproven by experiment.  For example, as Darwin noted, just a single instance of a
truely altruistic life form that would  give up its reproductive potential to
benefit that of another species would utterly and totally demolish his theory.
Creationism is not a scientific concept, as it can never been disproven by
experiment or observation.  There is no observation anyone can make that would in
anyway disprove it or any special form of it.  One could always hypothesize some
divine or supernatural intervention to explain any or all contrary results.  Such
ideas fall outside of science.  While there may well be great philosophic,
metaphysical, spiritual, or religous meaning to the infinite number of concepts
such as 2=3 or special forms of creationism and none of these disciplines are
excluded like science in their ability to evaluate these, scientists can neither
study them nor confuse such conceptual discussions with science.  You are quite
correct to think in terms of plausibily, as you look for explanation of natural
systems, since there are a great many uninteresting ideas that history has proven
are not worth wasting time over.  In my view creationism is clearly one of them.

Stuart G. Poss                       E-mail: Stuart.Poss at
Senior Research Scientist & Curator  Tel: (228)872-4238
Gulf Coast Research Laboratory       FAX: (228)872-4204
P.O. Box 7000
Ocean Springs, MS  39566-7000

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