Title: Re: paleonet Questions to Ask Your Biology
Professor
The National Center for Science Education
website has a page of answers to these questions:
http://www.ncseweb.org/resources/articles/7719_responses_to_jonathan_wells3_11_28_2001.asp
Q: ORIGIN OF LIFE. Why do textbooks
claim that the 1953 Miller-Urey experiment shows how life's building
blocks may have formed on the early Earth -- when conditions on the
early Earth were probably nothing like those used in the experiment,
and the origin of life remains a mystery?
A: Because evolutionary theory works
with any model of the origin of life on Earth, how life originated is
not a question about evolution. Textbooks discuss the 1953 studies
because they were the first successful attempt to show how organic
molecules might have been produced on the early Earth. When modern
scientists changed the experimental conditions to reflect better
knowledge of the Earth's early atmosphere, they were able to produce
most of the same building blocks. Origin-of-life remains a vigorous
area of research.
Why is this answer annoying? Because it makes no apology
for the fact that textbooks cite a 1953 experiment that employed
now-outdated ideas about early Earth environmental conditions.
Why not cite the more recent experiments with more refined ideas about
the environment? If the Urey-Miller experiment is mentioned at
all, it should be in the context of more research, not the reverse.
This sort of presentation gives students the idea that science has all
been "done" a long time ago.
Q: DARWIN'S TREE OF LIFE. Why don't
textbooks discuss the "Cambrian explosion," in which all
major animal groups appear together in the fossil record fully formed
instead of branching from a common ancestor -- thus contradicting the
evolutionary tree of life?
A: Wells is wrong: fish, amphibians,
reptiles, birds, and mammals all are post-Cambrian - aren't these
"major groups"? We would recognize very few of the Cambrian
organisms as "modern"; they are in fact at the roots of the
tree of life, showing the earliest appearances of some key features of
groups of animals - but not all features and not all groups.
Researchers are linking these Cambrian groups using not only fossils
but also data from developmental biology.
Another really annoying answer. Wells is obviously
referring to the fact that members of the vertebrate ancestral
group appeared during the Cambrian explosion. The truth is that
we haven't yet discovered the common ancestor in the fossil record.
Again, this is something to get students excited about: there is
work to do. Lots of it.
Q: HOMOLOGY. Why do textbooks define
homology as similarity due to common ancestry, then claim that it is
evidence for common ancestry -- a circular argument masquerading as
scientific evidence?
A: The same anatomical structure (such as a leg or an antenna) in
two species may be similar because it was inherited from a common
ancestor (homology) or because of similar adaptive pressure
(convergence). Homology of structures across species is not assumed,
but tested by the repeated comparison of numerous features that do or
do not sort into successive clusters. Homology is used to test
hypotheses of degrees of relatedness. Homology is not "evidence"
for common ancestry: common ancestry is inferred based on many sources
of information, and reinforced by the patterns of similarity and
dissimilarity of anatomical structures.
A very dry and self-satisfied answer that would drive students to
distraction. It is much better to employ an analogy here.
I use household appliances. A microwave oven and an electric
oven are convergent. They have separate origins technologically,
but resemble one another because they are developed for the same
purpose. An electric oven and a toaster are homologs. They
share technological attributes (the heating element most obviously)
that have been developed into somewhat different forms for slightly
different purposes.
Analogies force students to look for the conceptual level in a
topic. Merely presenting more detailed information does not
because they will be able to simply memorize it (or not). The
above analogy employs "designed objects" and would lead
rather naturally into a discussion of "intelligent
design".
***
I am not going to go through all ten of these. I think I've
made my point.
Bill
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William P. Chaisson
Adjunct Assistant Professor
Department of Earth and Environmental Sciences
University of Rochester
Rochester, NY 14627
607-387-3892