ICONS OF EVOLUTION? WHY MUCH OF WHAT JONATHAN WELLS WRITES ABOUT EVOLUTION IS WRONG
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ICONS OF EVOLUTION? WHY MUCH OF WHAT JONATHAN
WELLS WRITES ABOUT EVOLUTION IS WRONG
ALAN D. GISHLICK
NATIONAL CENTER FOR SCIENCE EDUCATION
INTRODUCTION that are commonly used to help to teach evolu-
tion. Wells calls these the “icons,” and brands
THE PARADIGM OF EVOLUTION them as false, out of date, and misleading.
volution is the unifying paradigm, the Wells then evaluates ten “widely used” high
E organizing principle of biology.
Paradigms are accepted for their overall
explanatory power, their “best fit” with all the
school and college biology textbooks for seven
of these “icons” with a grading scheme that he
constructed. Based on this, he claims that their
treatments of these icons are so rife with inac-
available data in their fields. A paradigm func-
tions as the glue that holds an entire discipline curacies, out-of-date information, and down-
together, connecting disparate subfields and right falsehoods that their discussions of the
relating them to one another. A paradigm is icons should be discarded, supplemented, or
also important because it fosters a research amended with “warning labels” (which he pro-
program, creating a series of questions that vides).
give researchers new directions to explore in According to Wells, the “icons” are the
order to better understand the phenomena Miller-Urey experiment, Darwin’s tree of life,
being studied. For example, the unifying para- the homology of the vertebrate limbs,
digm of geology is plate tectonics; although Haeckel’s embryos, Archaeopteryx, the pep-
not all geologists work on it, it connects the pered moths, and “Darwin’s” finches.
entire field and organizes the various disci- (Although he discusses three other “icons” —
plines of geology, providing them with their four-winged fruit flies, horse evolution, and
research programs. A paradigm does not stand human evolution — he does not evaluate text-
or fall on a single piece of evidence; rather, it books’ treatments of them.) Wells is right
is justified by its success in overall explanato- about at least one thing: these seven examples
ry power and the fostering of research ques- do appear in nearly all biology textbooks. Yet
tions. A paradigm is important for the ques- no textbook presents the “icons” as a list of our
tions it leads to, rather than the answers it “best evidence” for evolution, as Wells
gives. Therefore, the health of a scientific field implies. The “icons” that Wells singles out are
is based on how well its central theory explains discussed in different parts of the textbooks for
all the available data and how many new different pedagogical reasons. The Miller-
research directions it is spawning. By these Urey experiment isn’t considered “evidence
criteria, evolution is a very healthy paradigm for evolution”; it is considered part of the
for the field of biology. experimental research about the origin of life
In his book Icons of Evolution (2000), and is discussed in chapters and sections on the
Jonathan Wells attempts to overthrow the par- “history of life.” Likewise, Darwin’s finches
adigm of evolution by attacking how we teach are used as examples of an evolutionary
it. In this book, Wells identifies ten examples process (natural selection), not as evidence for
1Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
evolution. Archaeopteryx is frequently pre- 2000: xii). This is a serious charge; to support
sented in discussions of the origin of birds, not it demands the highest level of scholarship on
as evidence for evolution itself. Finally, text- the part of the author.
books do not present a single “tree of life”; Does Wells display this level of scholar-
rather, they present numerous topic-specific ship? Is Wells right? Are the “icons” out-of-
phylogenetic trees to show how relevant date and in need of removal? And more impor-
organisms are related. Wells’s entire discus- tantly, is there something wrong with the theo-
sion assumes that the evidence for evolution is ry of evolution?
a list of facts stored somewhere, rather than the In the following sections, each textbook
predictive value of the theory in explaining the “icon” is reexamined in light of Wells’s criti-
patterns of the past and present biological cism. The textbooks covered by Wells are
world. examined as well, along with the grading cri-
TEXTBOOK “ICONS”: teria (given in the appendix of Icons [Wells,
WHY DO WE HAVE THEM? 2000] and on the Discovery Institute’s web-
Paradigms and all their components are not site) that he used to assess their accuracy. What
necessarily simple. To understand the depth of was found is that although the textbooks could
any scientific field fully requires many years always benefit from improvement, they do not
of study. It is the goal of elementary and sec- mislead, much less “systematically misin-
ondary education to give students a basic form,” students about the theory of biological
understanding of the “world as we know it,” evolution or the evidence for it. Further, the
which includes teaching students the para- grading criteria Wells applied are vague and at
digms of a number of fields of science. In times appear to have been manipulated to give
order to do this, teaching examples must be poor grades. Many of the grades given are not
found. It is this need to find simple, easy-to- in agreement with the stated criteria or an
explain, dynamic, and visual examples to accurate reading of the evaluated text. Beyond
introduce a complex topic to students that has that, Icons of Evolution offers little in the way
led to the common use of a few examples — of suggestions for improvement of, or changes
the “icons.” Yet, with our knowledge of the in, the standard biology curriculum. When
natural world expanding at near-exponential Wells says that textbooks are in need of cor-
rates, the volume of new information facing a rection, he apparently means the removal of
textbook writer is daunting. The aim of a text- the subject of evolution entirely or the teaching
book is not necessarily to report the “state of of “evidence against” evolution, rather than
the art” as much as it is to offer an introduction the fixing of some minor errors in the presen-
to the basic principles and ideas of a certain tation of the putative “icons.” This makes
field. Therefore, it should not be surprising Icons of Evolution useful at most for those
that introductory textbooks are frequently sim- with a certain political and religious agenda,
plified and may be somewhat out-of-date. In but of little value to educators.
Icons of Evolution, however, Wells makes an
even stronger accusation. Wells says: References
“Students and the public are being systemati- Wells, J. 2000. Icons of evolution: science or myth?:
cally misinformed about the evidence for evo- why much of what we teach about evolution is wrong.
lution” through biology textbooks (Wells, Regnery, Washington DC, 338p.
2Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
THE MILLER-UREY how the early atmosphere was probably differ-
EXPERIMENT ent from the atmosphere hypothesized in the
original experiment. Wells then claims that the
THE EXPERIMENT ITSELF actual atmosphere of the early earth makes the
he understanding of the origin of life Miller–Urey type of chemical synthesis
T was largely speculative until the 1920s,
when Oparin and Haldane, working
independently, proposed a theoretical model
impossible, and asserts that the experiment
does not work when an updated atmosphere is
used. Therefore, textbooks should either dis-
cuss the experiment as an historically interest-
for “chemical evolution.” The Oparin–
Haldane model suggested that under the ing yet flawed exercise, or not discuss it at all.
strongly reducing conditions theorized to have Wells concludes by saying that textbooks
been present in the atmosphere of the early should replace their discussions of the Miller–
earth (between 4.0 and 3.5 billion years ago), Urey experiment with an “extensive discus-
inorganic molecules would spontaneously sion” of all the problems facing research into
form organic molecules (simple sugars and the origin of life.
amino acids). In 1953, Stanley Miller, along These allegations might seem serious; how-
with his graduate advisor Harold Urey, tested ever, Wells’s knowledge of prebiotic chemistry
this hypothesis by constructing an apparatus is seriously flawed. First, Wells’s claim that
that simulated the Oparin-Haldane “early researchers are ignoring the new atmospheric
earth.” When a gas mixture based on predic- data, and that experiments like the Miller–
tions of the early atmosphere was heated and Urey experiment fail when the atmospheric
given an electrical charge, organic compounds composition reflects current theories, is simply
were formed (Miller, 1953; Miller and Urey, false. The current literature shows that scien-
1959). Thus, the Miller-Urey experiment tists working on the origin and early evolution
demonstrated how some biological molecules, of life are well aware of the current theories of
such as simple amino acids, could have arisen the earth’s early atmosphere and have found
abiotically, that is through non-biological that the revisions have little effect on the
processes, under conditions thought to be sim- results of various experiments in biochemical
ilar to those of the early earth. This experiment synthesis. Despite Wells’s claims to the con-
provided the structure for later research into trary, new experiments since the Miller–Urey
the origin of life. Despite many revisions and ones have achieved similar results using vari-
additions, the Oparin–Haldane scenario ous corrected atmospheric compositions
remains part of the model in use today. The (Figure 1; Rode, 1999; Hanic et al., 2000).
Miller–Urey experiment is simply a part of the Further, although some authors have argued
experimental program produced by this para- that electrical energy might not have efficient-
digm. ly produced organic molecules in the earth’s
early atmosphere, other energy sources such as
WELLS BOILS OFF cosmic radiation (e.g., Kobayashi et al., 1998),
ells says that the Miller–Urey exper-
W
high temperature impact events (e.g.,
iment should not be taught because Miyakawa et al., 2000), and even the action of
the experiment used an atmospheric waves on a beach (Commeyras et al., 2002)
composition that is now known to be incorrect. would have been quite effective.
Wells contends that textbooks don’t discuss Even if Wells had been correct about the
3Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
Researcher(s) Year Reactants Energy source Results Probability
Miller 1953 CH4, NH3, H2O, H2 Electric discharge Simple amino acids, unlikely
organic compounds
Abelson 1956 CO, CO2, N2, NH3, H2, Electric discharge Simple amino acids, unlikely
H2O HCN
Groth and Weyssenhoff 1957 CH4, NH3, H2O Ultraviolet light Simple amino acids (low under special conditions
(1470–1294 ?) yields)
Bahadur, et al. 1958 Formaldehyde, Sunlight Simple amino acids possible
molybdenum oxide (photosynthesis)
Pavolvskaya and 1959 Formaldehyde, nitrates High pressure Hg lamp Simple amino acids possible
Pasynskii (photolysis)
Palm and Calvin 1962 CH4, NH3, H2O Electron irradiation Glycine, alanine, aspartic under special conditions
acid
Harada and Fox 1964 CH4, NH3, H2O Thermal energy 14 of the “essential” under special conditions
(900–1200º C) amino acids of proteins
Oró 1968 CH4, NH3, H2O Plasma jet Simple amino acids unlikely
Bar-Nun et al. 1970 CH4, NH3, H2O Shock wave Simple amino acids under special conditions
Sagan and Khare 1971 CH4, C2H6, NH3, H2O, Ultraviolet light (>2000 Simple amino acids (low under special conditions
H2S ?) yields)
Yoshino et al. 1971 H2, CO, NH3, Temperature of 700°C Glycine, alanine, unlikely
montmorillonite glutamic acid, serine,
aspartic acid, leucine,
lysine, arginine
Lawless and Boynton 1973 CH4, NH3, H2O Thermal energy Glycine, alanine, aspartic under special conditions
acid, ?-alanine,
N-methyl-?-alanine,
?-amino-n-butyric acid.
Yanagawa et al. 1980 Various sugars, Temperature of 105°C Glycine, alanine, serine, under special conditions
hydroxylamine, aspartic acid, glutamic
inorganic salts, acid
Kobayashi et al. 1992 CO, N2, H2O Proton irradiation Glycine, alanine, aspartic possible
acid, ?-alanine,
glutamic acid,
threonine,
?-aminobutyric acid,
serine
Hanic, et al. 1998 CO2, N2, H2O Electric discharge Several amino acids possible
Figure 1. A table of some amino acid synthesis experiments since Miller–Urey. The “probabili-
ty” column reflects the likelihood of the environmental conditions used in the experiment.
Modified from Rode, 1999.
Miller–Urey experiment, he does not explain since 1961 (see Oró, 1961; Whittet, 1997;
that our theories about the origin of organic Irvine, 1998). Wells apparently missed the vast
“building blocks” do not depend on that exper- body of literature on organic compounds in
iment alone (Orgel, 1998a). There are other comets (e.g. Oró, 1961; Anders, 1989; Irvine,
sources for organic “building blocks,” such as 1998), carbonaceous meteorites (e.g., Kaplan
meteorites, comets, and hydrothermal vents. et al., 1963; Hayes, 1967; Chang, 1994;
All of these alternate sources for organic mate- Maurette, 1998; Cooper et al., 2001), and con-
rials and their synthesis are extensively dis- ditions conducive to the formation of organic
cussed in the literature about the origin of life, compounds that exist in interstellar dust clouds
a literature that Wells does not acknowledge. (Whittet, 1997).
In fact, what is most striking about Wells’s Wells also fails to cite the scientific litera-
extensive reference list is the literature that he ture on other terrestrial conditions under which
has left out. Wells does not mention extrater- organic compounds could have formed. These
restrial sources of organic molecules, which non-atmospheric sources include the synthesis
have been widely discussed in the literature of organic compounds in a reducing ocean
4Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
(e.g., Chang, 1994), at hydrothermal vents troversy is really over why it took so long for
(e.g., Andersson, 1999; Ogata et al., 2000), and oxygen levels to start to rise. Current data
in volcanic aquifers (Washington, 2000). A show that oxygen levels did not start to rise
cursory review of the literature finds more than significantly until nearly 1.5 billion years after
40 papers on terrestrial prebiotic chemical syn- life originated (Rye and Holland, 1998;
thesis published since 1997 in the journal Copley, 2001). Wells strategically fails to clar-
Origins of life and the evolution of the bios- ify what he means by “early” when he discuss-
phere alone. Contrary to Wells’s presentation, es the amount of oxygen in the “early” atmos-
there appears to be no shortage of potential phere. In his discussion, he cites research
sources for organic “building blocks” on the about the chemistry of the atmosphere without
early earth. distinguishing whether the authors are refer-
Instead of discussing this literature, Wells ring to times before, during, or after the period
raises a false “controversy” about the low when life is thought to have originated. Nearly
amount of free oxygen in the early atmos- all of the papers he cites deal with oxygen lev-
phere. Claiming that this precludes the sponta- els after 3.0 billion years ago. They are irrele-
neous origin of life, he concludes that vant, as chemical data suggest that life arose
“[d]ogma had taken the place of empirical sci- 3.8 billion years ago (Chang, 1994; Orgel,
ence” (Wells, 2000:18). In truth, nearly all 1998b), well before there was enough free
researchers who work on the early atmosphere oxygen in the earth’s atmosphere to prevent
hold that oxygen was essentially absent during Miller–Urey-type chemical synthesis.
the period in which life originated (Copley, Finally, the Miller–Urey experiment tells us
2001) and therefore oxygen could not have nothing about the other stages in the origin of
played a role in preventing chemical synthesis. life, including the formation of a simple genet-
This conclusion is based on many sources of ic code (PNA or “peptide”-based codes and
data, not “dogma.” Sources of data include RNA-based codes) or the origin of cellular
fluvial uraninite sand deposits (Rasmussen and membranes (liposomes), some of which are
Buick, 1999) and banded iron formations discussed in all the textbooks that Wells
(Nunn, 1998; Copley, 2001), which could not reviewed. The Miller–Urey experiment only
have been deposited under oxidizing condi- showed one possible route by which the basic
tions. Wells also neglects the data from pale- components necessary for the origin of life
osols (ancient soils) which, because they form could have been created, not how life came to
at the atmosphere–ground interface, are an be. Other theories have been proposed to
excellent source to determine atmospheric bridge the gap between the organic “building
composition (Holland, 1994). Reduced pale- blocks” and life. The “liposome” theory deals
osols suggest that oxygen levels were very low with the origin of cellular membranes, the
before 2.1 billion years ago (Rye and Holland, RNA-world hypothesis deals with the origin of
1998). There are also data from mantle chem- a simple genetic code, and the PNA (peptide-
istry that suggest that oxygen was essentially based genetics) theory proposes an even sim-
absent from the earliest atmosphere (Kump et pler potential genetic code (Rode, 1999). Wells
al., 2001). Wells misrepresents the debate as doesn’t really mention any of this except to
over whether oxygen levels were 5/100 of 1%, suggest that the “RNA world” hypothesis was
which Wells calls “low,” or 45/100 of 1%, proposed to “rescue” the Miller–Urey experi-
which Wells calls “significant.” But the con- ment. No one familiar with the field or the evi-
5Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
dence could make such a fatuous and inaccu- deep-sea hydrothermal vents (Figure 2). No
rate statement. The Miller–Urey experiment is textbook claims that these experiments conclu-
not relevant to the RNA world, because RNA sively show how life originated; and all text-
was constructed from organic “building books state that the results of these experi-
blocks” irrespective of how those compounds ments are tentative.
came into existence (Zubay and Mui, 2001). It is true that some textbooks do not mention
The evolution of RNA is a wholly different that our knowledge of the composition of the
chapter in the story of the origin of life, one to atmosphere has changed. However, this does
which the validity of the Miller–Urey experi- not mean that textbooks are “misleading” stu-
ment is irrelevant. dents, because there is more to the origin of
WHAT THE TEXTBOOKS SAY life than just the Miller–Urey experiment.
Most textbooks already discuss this fact. The
ll of the textbooks reviewed contain a
A section on the Miller–Urey experi-
ment. This is not surprising given the
experiment’s historic role in the understanding
textbooks reviewed treat the origin of life with
varying levels of detail and length in “Origin
of life” or “History of life” chapters. These
chapters are from 6 to 24 pages in length. In
of the origin of life. The experiment is usually this relatively short space, it is hard for a text-
discussed over a couple of paragraphs (see book, particularly for an introductory class like
Figure 2), a small proportion (roughly 20%) of high school biology, to address all of the
the total discussion of the origin and early evo- details and intricacies of origin-of-life research
lution of life. Commonly, the first paragraph that Wells seems to demand. Nearly all texts
discusses the Oparin-Haldane scenario, and begin their origin of life sections with a brief
then a second outlines the Miller–Urey test of description of the origin of the universe and
that scenario. All textbooks contain either a the solar system; a couple of books use a dis-
drawing or a picture of the experimental appa- cussion of Pasteur and spontaneous generation
ratus and state that it was used to demonstrate instead (and one discusses both). Two text-
that some complex organic molecules (e.g., books discuss how life might be defined.
simple sugars and amino acids, frequently Nearly all textbooks open their discussion of
called “building blocks”) could have formed the origin of life with qualifications about how
spontaneously in the atmosphere of the early the study of the origin of life is largely hypo-
earth. Textbooks vary in their descriptions of thetical and that there is much about it that we
the atmospheric composition of the early earth. do not know.
Five books present the strongly reducing
atmosphere of the Miller–Urey experiment, WELLS’S EVALUATION
whereas the other five mention that the current s we will see in his treatment of the
geochemical evidence points to a slightly
reducing atmosphere. All textbooks state that
oxygen was essentially absent during the peri-
A other “icons,” Wells’s criteria for judg-
ing textbooks stack the deck against
them, ensuring failure. No textbook receives
od in which life arose. Four textbooks mention better than a D for this “icon” in Wells’s eval-
that the experiment has been repeated success- uation, and 6 of the 10 receive an F. This is
fully under updated conditions. Three text- largely a result of the construction of the grad-
books also mention the possibility of organic ing criteria. Under Wells’s criteria (Wells,
molecules arriving from space or forming at 2000:251–252), any textbook containing a pic-
6Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
Figure 2. Textbook treatments of the Miller–Urey experiment. Textbooks are listed in order of
increasing detail (AP/College textbooks highlighted; note that Futuyma is an upper-level col-
lege/graduate textbook).
ture of the Miller–Urey apparatus could pictures. Wells’s criteria would require that
receive no better than a C, unless the caption of even the intelligent design “textbook” Of
the picture explicitly says that the experiment Pandas and People would receive a C for its
is irrelevant, in which case the book would treatment of the Miller–Urey experiment.
receive a B. Therefore, the use of a picture is In order to receive an A, a textbook must
the major deciding factor on which Wells eval- first omit the picture of the Miller–Urey appa-
uated the books, for it decides the grade irre- ratus (or state explicitly in the caption that it
spective of the information contained in the was a failure), discuss the experiment, but then
text! A grade of D is given even if the text state that it is irrelevant to the origin of life.
explicitly points out that the experiment used This type of textbook would be not only scien-
an incorrect atmosphere, as long as it shows a tifically inaccurate but pedagogically defi-
picture. Wells pillories Miller and Levine for cient.
exactly that, complaining that they bury the
correction in the text. This is absurd: almost all
textbooks contain pictures of experimental
apparatus for any experiment they discuss. It is WHY WE SHOULD STILL TEACH
the text that is important pedagogically, not the MILLER–UREY
7Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
he Miller–Urey experiment represents
T
of scientific understanding of the origin of life.
one of the research programs spawned This is the kind of “good science” that we want
by the Oparin-Haldane hypothesis. to teach students.
Even though details of the model for the origin Finally, the Miller–Urey experiment should
of life have changed, this has not affected the still be taught because the basic results are still
basic scenario of Oparin–Haldane. The first valid. The experiments show that organic mol-
stage in the origin of life was chemical evolu- ecules can form under abiotic conditions. Later
tion. This involves the formation of organic experiments have used more accurate atmos-
compounds from inorganic molecules already pheric compositions and achieved similar
present in the atmosphere and in the water of results. Even though origin-of-life research has
the early earth. This spontaneous organization moved beyond Miller and Urey, their experi-
of chemicals was spawned by some external ments should be taught. We still teach Newton
energy source. Lightning (as Oparin and even though we have moved beyond his work
Haldane thought), proton radiation, ultraviolet in our knowledge of planetary mechanics.
radiation, and geothermal or impact-generated Regardless of whether any of our current theo-
heat are all possibilities. ries about the origin of life turn out to be com-
The Miller–Urey experiment represents a pletely accurate, we currently have models for
major advance in the study of the origin of life. the processes and a research program that
In fact, it marks the beginning of experimental works at testing the models.
research into the origin of life. Before Miller–
Urey, the study of the origin of life was mere- HOW TEXTBOOKS COULD IMPROVE
THEIR PRESENTATIONS OF
ly theoretical. With the advent of “spark exper-
THE ORIGIN OF LIFE
iments” such as Miller conducted, our under-
extbooks can always improve discus-
standing of the origin of life gained its first
experimental program. Therefore, the Miller–
Urey experiment is important from an histori-
cal perspective alone. Presenting history is
T sions of their topics with more up-to-
date information. Textbooks that have
not already done so should explicitly correct
good pedagogy because students understand the estimate of atmospheric composition, and
scientific theories better through narratives. accompany the Miller–Urey experiment with a
The importance of the experiment is more than clarification of the fact that the corrected
just historical, however. The apparatus Miller atmospheres yield similar results. Further, the
and Urey designed became the basis for many wealth of new data on extraterrestrial and
subsequent “spark experiments” and laid a hydrothermal sources of biological material
groundwork that is still in use today. Thus it is should be discussed. Finally, textbooks ideally
also a good teaching example because it shows should expand their discussions of other stages
how experimental science works. It teaches in the origin of life to include PNA and some
students how scientists use experiments to test of the newer research on self-replicating pro-
ideas about prehistoric, unobserved events teins. Wells, however, does not suggest that
such as the origin of life. It is also an interest- textbooks should correct the presentation of
ing experiment that is simple enough for most the origin of life. Rather, he wants textbooks to
students to grasp. It tested a hypothesis, was present this “icon” and then denigrate it, in
reproduced by other researchers, and provided order to reduce the confidence of students in
new information that led to the advancement the possibility that scientific research can ever
8Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
establish a plausible explanation for the origin Organic compounds in stony meteorites. Geochimica et
of life or anything else for that matter. If Cosmochimica Acta. 27:805–834.
Wells’s recommendations are followed, stu- Kobayashi, K., T. Kaneko, T. Saito, and T. Oshima.
1998. Amino acid formation in gas mixtures by high
dents will be taught that because one experi-
energy particle irradiation. Origins of Life and the
ment is not completely accurate (albeit in hind- Evolution of the Biosphere 28:155–165.
sight), everything else is wrong as well. This is Kump, L. R., J. F. Kasting, M. E. Barley. 2001. Rise of
not good science or science teaching. atmospheric oxygen and the “upside-down” Archean
mantle. Geochemistry, Geophysics, Geosystems –G3, 2,
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York. p. 237–244. Rye, R., and H. D. Holland. 1998. Paleosols and the
Irvine, W. M., 1998. Extraterrestrial organic matter: a evolution of atmospheric oxygen: a critical review.
review. Origins of Life and the Evolution of the American Journal of Science 298:621–672.
Biosphere 28:365–383. Washington, J. 2000. The possible role of volcanic
Kaplan, I. R., E. T. Degens, and J. H. Reuter. 1963. aquifers in prebiologic genesis of organic compounds
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Alan D. Gishlick, National Center for Science Education
and RNA. Origins of Life and the Evolution of the
Biosphere 30: 53–79.
Wells, J. 2000. Icons of evolution: science or myth?:
why much of what we teach about evolution is wrong.
Regnery, Washington DC, 338p.
Whittet, D. C. B. 1997. Is extraterrestrial organic matter
relevant to the origin of life on earth? Origins of Life
and the Evolution of the Biosphere 27: 249–262.
Zubay, G. and T. Mui. 2001. Prebiotic synthesis of
nucleotides. Origins of Life and Evolution of the
Biosphere 31:87–102.
10Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
DARWIN’S “TREE OF LIFE” mon descent. Finally, he demands that text-
books treat universal common ancestry as
PHYLOGENETIC TREES unproven and refrain from illustrating that
n biology, a phylogenetic tree, or phyloge- “theory” with misleading phylogenies.
I ny, is used to show the genealogic relation-
ships of living things. A phylogeny is not
so much evidence for evolution as much as it
Therefore, according to Wells, textbooks
should state that there is no evidence for com-
mon descent and that the most recent research
refutes the concept entirely. Wells is complete-
is a codification of data about evolutionary his-
tory. According to biological evolution, organ- ly wrong on all counts, and his argument is
isms share common ancestors; a phylogeny entirely based on misdirection and confusion.
shows how organisms are related. The tree of He mixes up these various topics in order to
life shows the path evolution took to get to the confuse the reader into thinking that when
current diversity of life. It also shows that we combined, they show an endemic failure of
can ascertain the genealogy of disparate living evolutionary theory. In effect, Wells plays the
organisms. This is evidence for evolution only equivalent of an intellectual shell game, put-
in that we can construct such trees at all. If ting so many topics into play that the “ball” of
evolution had not happened or common ances- evolution gets lost.
try were false, we would not be able to discov- THE CAMBRIAN EXPLOSION
er hierarchical branching genealogies for
ells claims that the Cambrian
organisms (although textbooks do not general-
ly explain this well). Referring to any phylo-
genetic tree as “Darwin’s tree of life” is some-
what of a misnomer. Darwin graphically pre-
W Explosion “presents a serious chal-
lenge to Darwinian evolution”
(Wells, 2000:41) and the validity of phyloge-
netic trees. The gist of Wells’s argument is that
sented no phylogenies in the Origin of Species;
the Cambrian Explosion happened too fast to
the only figure there depicts differential rates
allow large-scale morphological evolution to
of speciation. If anyone deserves credit for
occur by natural selection (“Darwinism”), and
giving us “trees of life,” it is Ernst Haeckel,
that the Cambrian Explosion shows “top-
who drew phylogenies for many of the living
down” origination of taxa (“major” “phyla”
groups of animals literally as trees, as well as
level differences appear early in the fossil
coining the term itself.
record rather than develop gradually), which
WELLS’S SHELL GAME he claims is the opposite of what evolution
ells uses phylogenetic trees to attack predicts. He asserts that phylogenetic trees
W the very core of evolution — com-
mon descent. Wells claims that text-
books mislead students about common descent
predict a different pattern for evolution than
what we see in the Cambrian Explosion. These
arguments are spurious and show his lack of
in three ways. First, Wells claims that text- understanding of basic aspects of both paleon-
books do not cover the “Cambrian Explosion” tology and evolution.
and fail to point out how this “top-down” pat- Wells mistakenly presents the Cambrian
tern poses a serious challenge to common Explosion as if it were a single event. The
descent and evolution. Second, he asserts that Cambrian Explosion is, rather, the preserva-
the occasional disparity between morphologi- tion of a series of faunas that occur over a 15–
cal and molecular phylogenies disproves com- 20 million year period starting around 535 mil-
11Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
lion years ago (MA). A fauna is a group of claiming that this proves that the fossil record
organisms that live together and interact as an is complete enough to show that there were no
ecosystem; in paleontology, “fauna” refers to a precursors for the Cambrian Explosion ani-
group of organisms that are fossilized together mals. This claim is false. His evidence for this
because they lived together. The first fauna “well documented” Precambrian fossil record
that shows extensive body plan diversity is the is a selective quote from the final sentence in
Sirius Passet fauna of Greenland, which is an article by Benton et al. (2000). While the
dated at around 535 MA (Conway Morris, paper’s final sentence does literally say that
2000). The organisms preserved become more the “early” parts of the fossil record are ade-
diverse by around 530 MA, as the Chenjiang quate for studying the patterns of life, Wells
fauna of China illustrates (Conway Morris, leaves out a critical detail: the sentence refers
2000). Wells erroneously claims that the not to the Precambrian, but to the Cambrian
Chenjiang fauna predates the Sirius Passet and later times. Even more ironic is the fact
(Wells, 2000:39). The diversification contin- that the conclusion of the paper directly refutes
ues through the Burgess shale fauna of Canada Wells’s claim that the fossil record does not
at around 520 MA, when the Cambrian faunas support the “tree of life.” Benton et al. (2000)
are at their peak (Conway Morris, 2000). Wells assessed the completeness of the fossil record
makes an even more important paleontological using both molecular and morphological
error when he does not explain that the “explo- analyses of phylogeny. They showed that the
sion” of the late Early and Middle Cambrian is sequence of appearance of major taxa in the
preceded by the less diverse “small shelly” fossil record is consistent with the pattern of
metazoan faunas, which appear at the begin- phylogenetic relationships of the same taxa.
ning of the Cambrian (545 MA). These faunas Thus they concluded that the fossil record is
are dated to the early Cambrian, not the consistent with the tree of life, entirely oppo-
Precambrian as stated by Wells (Wells, site to how Wells uses their paper.
2000:38). This enables Wells to omit the Wells further asserts that there is no evi-
steady rise in fossil diversity over the ten mil- dence for metazoan life until “just before” the
lion years between the beginning of the Cambrian explosion, thereby denying the nec-
Cambrian and the Cambrian Explosion (Knoll essary time for evolution to occur. Yet Wells is
and Carroll, 1999). evasive about what counts as “just before” the
In his attempt to make the Cambrian Cambrian. Cnidarian and possible arthropod
Explosion seem instantaneous, Wells also embryos are present 30 million years “just
grossly mischaracterizes the Precambrian fos- before” the Cambrian (Xiao et al., 1998).
sil record. In order to argue that there was not There is also a mollusc, Kimberella, from the
enough time for the necessary evolution to White Sea of Russia (Fedonkin and Waggoner,
occur, Wells implies that there are no fossils in 1997) dated approximately 555 million years
the Precambrian record that suggest the com- ago, or 10 million years “just before” the
ing diversity or provide evidence of more Cambrian (Martin et al., 2000). This primitive
primitive multicellular animals than those seen animal has an uncalcified “shell,” a muscular
in the Cambrian Explosion (Wells, 2000:42– foot (Fedonkin and Waggoner, 1997), and a
45). He does this not by producing original radula inferred from “mat-scratching” feeding
research, but by selectively quoting paleonto- patterns surrounding fossilized individuals
logical literature on the fossil record and (personal observation; Seilacher, pers.
12Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
comm.). These features enable us to recognize Cambrian Explosion, for example, is the first
it as a primitive relative of molluscs, even time we are able to distinguish a chordate from
though it lacks a calcified shell. There are also an arthropod. This does not mean that the chor-
Precambrian sponges (Gehling and Rigby, date or arthropod lineages evolved then, only
1996) as well as numerous trace fossils indi- that they then became recognizable as such.
cating burrowing by wormlike metazoans For a simple example, consider the turtle. How
beneath the surface of the ocean’s floor do you know a turtle is a turtle? By the shell.
(Seilacher, 1994; Fedonkin, 1994). Trace fos- How would you recognize the ancestors of the
sils demonstrate the presence of at least one living turtle, before they evolved the shell?
ancestral lineage of bilateral animals nearly 60 That is more complicated. Because its ances-
million years “just” before the Cambrian tors would have lacked the diagnostic feature
(Valentine et al., 1999). Sixty million years is of a shell, ancestral turtles may be hard to rec-
approximately the same amount of time that ognize (Lee, 1993). In order to locate the
has elapsed since the extinction of non-avian remote ancestors of turtles, other, more subtle,
dinosaurs, providing plenty of time for evolu- features must be found.
tion. In treating the Cambrian Explosion as a Similarly, before the Cambrian Explosion,
single event preceded by nothing, Wells mis- there were lots of “worms,” now preserved as
represents fact — the Cambrian explosion is trace fossils (i.e., there is evidence of burrow-
not a single event, nor is it instantaneous and ing in the sediments). However, we cannot dis-
lacking in any precursors. tinguish the chordate “worms” from the mol-
Continuing to move the shells, Wells lusc “worms” from the arthropod “worms”
invokes a semantic sleight of hand in resur- from the worm “worms.” Evolution predicts
recting a “top-down” explanation for the diver- that the ancestor of all these groups was worm-
sity of the Cambrian faunas, implying that like, but which worm evolved the notochord,
phyla appear first in the fossil record, before and which the jointed appendages? In his argu-
lower categories. However, his argument is an ment, Wells confuses the identity of the indi-
artifact of taxonomic practice, not real mor- vidual with how we diagnose that identity, a
phology. In traditional taxonomy, the recogni- failure of logic that dogs his discussion of
tion of a species implies a phylum. This is due homology in the following chapter. If the ani-
to the rules of the taxonomy, which state that if mal does not have the typical diagnostic fea-
you find a new organism, you have to assign it tures of a known phylum, then we would be
to all the necessary taxonomic ranks. Thus unable to place it and (by the rules of taxono-
when a new organism is found, either it has to my) we would probably have to erect a new
be placed into an existing phylum or a new one phylum for it. When paleontologists talk about
has to be erected for it. Cambrian organisms the “sudden” origin of major animal “body
are either assigned to existing “phyla” or new plans,” what is “sudden” is not the appearance
ones are erected for them, thereby creating the of animals with a particular body plan, but the
effect of a “top-down” emergence of taxa. appearance of animals that we can recognize as
Another reason why the “higher” taxonom- having a particular body plan. Overall, howev-
ic groups appear at the Cambrian Explosion is er, the fossil record fits the pattern of evolu-
because the Cambrian Explosion organisms tion: we see evidence for worm-like bodies
are often the first to show features that allow first, followed by variations on the worm
us to relate them to living groups. The theme. Wells seems to ignore a growing body
13Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
Figure 3. Stepwise evolution of vertebrate features as illustrated by living and fossil animals.
of literature showing that there are indeed cally worms with a stiff rod (the notochord) in
organisms of intermediate morphology present them. The amount of change between a worm
in the Cambrian record and that the classic and a worm with a stiff rod is relatively small,
“phyla” distinctions are becoming blurred by but the presence of a notochord is a major
fossil evidence (Budd, 1998, 1999; Budd and “body-plan” distinction of a chordate. Further,
Jensen, 2000). it is just another small step from a worm with
Finally, the “top-down” appearance of a stiff rod to a worm with a stiff rod and a head
body-plans is, contrary to Wells, compatible (e.g., Haikouella; Chen et al., 1999) or a worm
with the predictions of evolution. The issue to with a segmented stiff rod (vertebrae), a head,
be considered is the practical one that “large- and fin folds (e.g., Haikouichthyes; Shu et al.,
scale” body-plan change would of course 1999). Finally add a fusiform body, fin differ-
evolve before minor ones. (How can you vary entiation, and scales: the result is something
the lengths of the beaks before you have a resembling a “fish” (Figure 3). But, as soon as
head?) The difference is that, many of the the stiff rod evolved, the animal was suddenly
“major changes” in the Cambrian were initial- no longer just a worm but a chordate — repre-
ly minor ones. Through time they became sentative of a whole new phylum! Thus these
highly significant and the basis for “body- “major” changes are really minor in the begin-
plans.” For example, the most primitive living ning, which is the Precambrian–Cambrian
chordate Amphioxus is very similar to the period with which we are concerned.
Cambrian fossil chordate Pikia. Both are basi-
14Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
CONGRUENCE OF PHYLOGENIES
BASED ON DIFFERENT
SOURCES OF DATA
ells also points to the occasional
W lack of congruence between molec-
ular- and morphology-based phylo-
genies as evidence against common descent.
(Molecular phylogenies are based on compar-
isons of the genes of organisms.) Wells omits
the fact that the discrepancies are frequently
small, and their causes are largely understood
(Patterson et al., 1993; Novacek, 1994).
Although not all of these discrepancies can yet
be corrected for, most genetic and morpholog-
ical phylogenies are congruent for 90% of the
Figure 4. Amniote relationships based on
taxa included. For example, all phylogenies,
different sources of data. Note that the only
whether morphological or molecular, consider
group whose position varies is turtles.
all animals bearing amniotic eggs to be more
closely related to one another than to amphib- a few possibilities (Rieppel and deBraga,
ians. Within this group, all reptiles and birds 1996; Lee, 1997; deBraga and Rieppel, 1997;
are more closely related to each other than they Zardoya and Meyer, 1998; Rieppel and Reiz,
are to mammals. Finally, birds and crocodiles 1999; Rieppel, 2000; Figure 4), and none of
are more closely related to each other than to these claim turtles are mammals. The uncer-
lizards, snakes, and the tuatara (Gauthier et al., tainty over the precise placement of turtles
1988; Gauthier, 1994). The only group whose with respect to other groups, however, does not
placement varies for both molecular and mor- mean that they did not evolve. Unfortunately,
phology data sets is turtles. This is due to a genes can never be totally compared to mor-
phenomenon called “long branch attraction” or phology since genetic trees cannot take fossil
the “Felsenstein Zone” (Huelsenbeck and taxa into account: genes don’t fossilize. No
Hillis, 1993). Long branch attraction is caused diagnostic tool of science is perfect. The
when a organism has had so much evolution- imperfections in phylogenetic reconstruction
ary change that it cannot be easily compared to do not make common ancestry false. Besides,
other organisms, and due to the nature of the are these extremely technical topics really
methodology used to evaluate phylogeny, it appropriate for introductory textbooks?
can appear to be related to many possible Instead of clearly discussing these actual
organisms (Felsenstein, 1978; Huelsenbeck phylogenetic issues, Wells invents one that
and Hillis, 1993). This is the case for turtles. isn’t even real. He cites a 1998 paper that
Turtles are so morphologically and genetically placed cows phylogenetically closer to whales
different from the rest of the reptiles that they than to horses, calling that finding “bizarre”
are hard to place phylogenetically (Zardoya (Wells, 2000:51). Yet this is not “bizarre” at
and Meyer, 2001). Still, researchers have nar- all; it was expected. All the paleontological
rowed down the possible turtle relationships to and molecular evidence points to a whale
15Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
orgin within artiodactyls, and further to the THE UNIVERSAL COMMON
fact that artiodactyls (cows, deer, antelopes, ANCESTOR
pigs, etc.) are not more closely related to peris- inally, Wells cites the “failure” of molec-
sodactyls (horses, rhinos, and the tapir) than
they are to whales (Novacek, 1992, 2001).
Wells makes this statement smugly, as if to
F ular phylogeny to clarify the position of
the Universal Common Ancestor as
proof that there is no common ancestry for any
suggest that everyone should think that this of life. Here, Wells mixes up the different
sounds silly. Unfortunately, it is Wells’s criti- scales of descent in order to tangle the reader
cism that is silly. in a thicket of phylogenetic branches. He is
Figure 5. The traditional view of phylogenetic relationships for the three “domains” of life com-
pared to Woese’s view. Note that the only difference lies in whether there is a single “root” at the
base of the tree. Regardless, eukaryotes, archaeans, and bacteria all share a common ancestor on
both, although Woese does posit a greater degree of lateral trasfer for single-celled organisms.
16Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
attacking the notion that life originated with pods, or angiosperms (Figure 5). That is still a
one population, and that all life can trace its lot of evolution that Wells’s inaccurate attack
ancestry back to that population, the Universal on the idea of a UCA does nothing to dispel.
Common Ancestor (UCA). The problem has WHAT THE TEXTBOOKS SAY
been that it is hard to determine relationships
he concept of common ancestry is at the
when there is nothing to compare to. How do
you compare “not life” to “life”? We have no
fossils of the earliest forms of life, and the high
degree of genetic change that has occurred in
T core of evolution. The very idea that
different species arise from previous
forms via descent implies that all living things
the 3.8 billion years since the early stages of share a common ancestral population at some
life make it nearly impossible to reconstruct point in their history. This concept is support-
the “original” genetic code. This does not ed by the fossil record, which shows a history
invalidate the concept of common ancestry; it of lineages changing through time. Because
just makes it difficult and potentially impossi- evolution is the basis for biology, it would be
ble to untangle the lineages. And this does not surprising if any textbook teaching contempo-
mean that there is not one real lineage: the rary biology would portray common descent
inability to determine the actual arrangement other than matter-of-factly.
of “domains” at the base of the tree or to char- Textbooks treat the concept of common
acterize the UCA does not make the UCA any descent in basically the same way as do scien-
less real than the inability to characterize light tists; they accept common ancestry of living
unambiguously as either a wave or a particle things as a starting point, and proceed from
makes light unreal. there. Phylogenies thus appear in many places
Some authors (e.g., Woese, 1998) go further in a text, which makes it very hard to evaluate
and suggest that there is no “UCA”; rather, exactly how textbooks “misrepresent” biologi-
they suggest, life arose in a soup of competing cal evolution using trees. Most texts show a
genomes. These genomes were constantly phylogeny in chapters discussing systematics
exchanging and mixing, and thus cellular life and taxonomy. In this section there is usually a
may have arisen multiple times. Wells misrep- tree of “kingdom” or “domain” relationships,
resents the statements of those scientists to which may be what Wells considers a tree
make it look as if they are questioning the showing “universal” common ancestry; unfor-
entirety of common ancestry, when what they tunately, his discussion is too vague for a read-
question is just the idea of a single common er to be sure whether that is what he is refer-
ancestor at the base of life. Further, when some ring to. Many textbooks show additional, more
suggest that we should abandon the search for detailed trees in their discussions of different
the UCA, they do not mean that they don’t taxonomic groups. In terms of textbook pre-
think it existed. They mean only that it may be sentations, then, there is no single “Darwin’s
a waste of time to try to find it given the cur- tree of life” presented in some iconic state, but
rent technology and methods at our disposal. many various phylogenies shown in the appro-
Regardless of the status of a UCA, which is at priate sections of most books. Textbooks also
the base of the tree of life, the entire debate has present trees in the chapters on processes and
nothing to do with the branches of the tree — mechanisms of evolution, in the “Origin of
the shared descent of eukaryotes, of animals, life” or “History of life” chapters, and in chap-
or common descent among vertebrates, arthro- ters dealing with individual taxonomic groups.
17Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
Figure 6. Evaluation of Wells’s grading of Textbook Icon #2, “Darwin’s Tree of Life.”
Parenthetical notations indicate the number of phylogenetic trees shown in the book.
18Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is Wrong
Alan D. Gishlick, National Center for Science Education
This is because phylogenetic trees are not part “explosion.” These discussions usually men-
of the “evidence for evolution,” but rather tion that it was a “rapid” origin of animal
graphical representations of the history, groups. Does Wells actually require that the
genealogy, and taxonomy of life. No textbook book explicitly mention the “Cambrian
misrepresents the methods that are used to Explosion” by name? If so, it should have been
construct trees or the trees themselves, specified in the criteria. Or is it that it he only
although some trees contain out-of-date rela- looked for “Cambrian Explosion” in the noto-
tionships and occasionally incorrect identifica- riously spotty indexes of the textbooks? A
tions of organisms pictured in them. When reevaluation suggests that five of the books to
textbooks cover the Cambrian period, the rapid which he gives an F should receive, even by
appearance of many body plans is discussed his criteria, a D. Finally, one text (Miller and
not as a “paradox” for evolutionary theory, but Levine’s) even mentions the confusing nature
as an interesting event in the history of life — of the basal divergence of life caused by later-
which is how paleontologists and evolutionary al transfer, yet this discussion can receive no
biologists consider it. credit in the grading. This is because although
WELLS’S EVALUATION Wells considers the “phylogenetic thicket” to
be extremely important to reject universal
verall, Wells’s grading system for this
O “icon” is so nebulous that it is hard to
figure out exactly how he evaluated
the textbooks at all. The “Universal Common
common ancestry, he apparently does not con-
sider it important enough to account for it in
his grading scheme. All of this calls into ques-
tion how well Wells actually reviewed the texts
Ancestor” is far different from the “Cambrian he graded as well as whether his grades have
Explosion.” These deal with very different any utility at all.
places in the “tree of life” as well as very dif-
ferent issues in evolution. Wells’s grades seem WHY WE SHOULD CONTINUE TO
largely based on presentations of “common TEACH COMMON DESCENT
here is no reason for textbooks to sig-
T
ancestry.” For example, according to Wells, if
the textbook treats common ancestry as “fact,” nificantly alter their presentations of
then it can do no better than a D. In order to get common descent or phylogenetic trees.
a C or better, a book must also discuss the As long as biological evolution is the paradigm
“top-down” nature of the Cambrian explosion of biology, common descent should be taught.
as a “problem” for evolution; if a book only All living organisms that reproduce have off-
mentions the Cambrian Explosion, it gets a D. spring that appear similar to, but not exactly
Here Wells does not even apply his grading like, their parents. We can observe descent
scheme consistently (Figure 6). For example, with modification every day, and like Darwin,
Wells chastises textbooks (Miller and Levine’s we can confidently extrapolate that it has gone
in particular) for not discussing the Cambrian on throughout the history of life. Through this
Explosion, yet most of the textbooks he process, small differences would accumulate
reviews actually mention it (Figure 6) and to larger differences and result in the evolution
Miller and Levine devote an entire page (p. of diversity that we see today and throughout
601) to it. Many of the reviewed textbooks dis- the history of life.
cuss the Cambrian period in the history of life The concept of descent allows us to make
sections, but do not specifically call it an testable predictions about the fossil record and
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