Download - The Problems of Evolution
AMDG
John Brodeur
The Problems of Evolution Book Report
For Professor Matthew McCann
Survey of Physical Science PHY 105
2 December 2008
The controversy of evolution seems to be over. Most scientists and
educators of our day simply overlook the questions it left unanswered. Evolution
is taught in schools as if it were a law. Almost every relevant modern theory of
science presupposes the evolutionary theory as the origin of species. Very few
dare challenge it; it has become as much a reality to most students as the law of
gravity. The great debate appears to have ended. The only substantial quarrels
still raging are heralded by a select few creationist extremists who refuse to argue
with scientific or philosophical ideas. As far as science goes, evolution has been
proven – or has it? Despite the breadth and development of the theory of evolution
over the years, there are still intricate questions which have remained unanswered
to this day. It seems common practice these days to leave these questions
unaddressed, to learn only the working elements of the theory of evolution. I have
always taken a personal interest in these overlooked “scientific problems” of
evolution, and I found it fitting to designate this second book report to this interest.
The book I have selected to accomplish this task was written by Mark Ridley and
is entitled The Problems of Evolution. As I have read through it, I have marveled
at its uniquely objective approach which seeks philosophical logical answers over
superficial ones. By the report I have provided below, I hope not only to peak the
reader‟s interest, but to encourage an intellectual engagement in the controversy of
evolution – which is, as Ridley makes clear, far from over.
In the preface of his work, Ridley states that his goal in writing this book has
been to set forth the problems of evolution which are timeless and investigate the
merits which those problems bring forth. Ridley desires not only to address
modern controversy but all controversy which is fundamental to a true
understanding of the evolutionary theory. The book is modeled after a similar
book by Bertrand Russell. However, as Ridley points out, science must be
differently approached than a book grounded in Platonic philosophy; it must
necessarily seek real tenable answers; it cannot leave open questions unanswered.
Many things, Ridley concedes, can be known and asserted as facts in science (such
as the science of genetics), and these are the very things which frame what Ridley
calls “a set of Great Questions” in evolutionary biology. These “Great Questions”
are the very controversy which science must continually strive to answer. Some
have been addressed and/or answered more effectively than others, and Ridley
makes it a point to proceed in sequence from the most concretely answered to the
least explored. In this way, Ridley begins his book on the problems of evolution.
The first question Ridley asks is whether or not evolution is true. The
unanimity of biologists, he remarks, should not be overlooked when answering
such a question, nor should it be taken for granted. Both common sense and the
authorities of history and modernity give witness to the immutability of species.
The arguments which can be pitted against these two authorities are those which
choose between evolution and the fixity of species. In recognizing this, Ridley
asserts that there are three possible theories to consider which are defined by two
questions: 1) whether species are immutable and 2) how many independent origins
of life there have been. In the case of evolution (Figure 1c), all species would have
descended from a single common ancestral series, diversifying through a period of
time and originating all at once. The diversity of species would have necessarily
resulted from a splitting of the species. If it was the case that species do change
but that life originated more than once, a second possible theory is born. Akin to
the theory of Lamarck is this theory that life has originated as many times as there
are modern species and that in each case the species has evolved but never split.
This hypothesis is known as transformism (Figure 1b). A last hypothesis is more
akin to a creationist approach wherein all species have looked the same in the past
and that all of them have separate origins; this is termed “separate creation” by
Ridley (Figure 1a).
Figure 1
The three kinds of evidence Ridley uses to test these theories are 1)
observation of evolution on a small scale, 2) the argument from classification, and
3) the fossil record. The best is the first of these. Evolution has indeed been
observed in both natural and artificial conditions. The peppered moth example
which Ridley elaborates upon demonstrates that a new generation which is
different from its ancestor can be produced by selective breeding. In any way
experimentation is done in this manner, the outcome will always favor either
evolution or transformism. It will not and cannot favor separate creation. It has
been proven time and time again that, especially in the fields of agriculture and
horticulture, new species come about in both the morphological and reproductive
interpretation of origin. Hybridization, then, seemingly destroys the hypothesis of
“separate creation,” and reasserts the common sense that species are not
immutable. Gradual changes in a species, particularly as illustrated by the many
gradations of the herring gull, could not possibly be accounted for by individual
creation. The idea of separate creation would ultimately lead to the conclusion that
every individual is created separately because each differs from the other in some
way, and this is simply not the case as we know the natural reproductive methods
by which creatures are born to the world. To check this idea would be to assert
that evolution takes place up to a certain point in the Linnaean hierarchy, but
because the degrees of difference are continuous, the point at which evolution
stops and separate creation begins creates an immediate paradox: if evolution could
produce all changes up to that point, why could it not produce the small alteration
between these next two levels? The philosophical principle of uniformitarianism,
the principle that an observed process over a short time could have operated for
longer to produce proportionately longer effects, is necessarily applied here. Just as
in all of science, uniformatarianism is the logical assumption which makes this
conclusion credible.
Now that the theory of separate creation has been ruled out, the theory of
transformism needs to be addressed; although Ridley has proven that species are
not fixed in form, he has yet to show that they all share a common ancestor. The
first proof of a common ancestor comes from the observation of hierarchical
classification. Although it is true that any set of objects can be classified
hierarchically, the method by which the Linnaean hierarchy is constructed is
special because it involves traits known as homologies. Homologies are traits that
are similar between species, but do not have to be because of functional necessity.
A striking example of this homology is found in the resemblance of a mammal‟s
ear-bone to the jaw-bone of reptiles. The fact that species share homologous
structures with other species is a strong case for evolution. This same argument
was the chief argument of Darwin‟s own example of the Galapagos finches. The
genetic code, according to Ridley, is by far the greatest argument of homology:
every organism is made up of the hereditary material known as DNA. In each
strand is a sequence made up of four bases symbolized by the letters A, C, G, and
T. In every amino acid there is a triplet of these bases, and in every protein, there
is a sequence of these amino acids. The homological wonder here is that for every
organism, the code is the same. Just like a language, the sequence need not
represent the same thing in each organism; the combination GGC could mean one
thing in one organism and something different in another, but this is not the case –
it means the same in every organism, namely glycine. This observation severely
weakens the theories of separate creation and transformism.
The third and last argument for evolution is the fossil record. Ridley admits
in this argument that the record of evolutionary change within single lineages is
very poor. If evolution were true, one would expect to find more changes in the
fossil record; the rarity of fossils can most definitely be a deterrent to this argument
on a local level. If one were to observe the fossil record as a whole, however, he
would take notice of the importance of sequence in the fossil record. When one
observes the sequence of vertebrates, he will find first fish, then amphibians, then
reptiles, and then mammals, a clear sequence of more mammal-like reptiles in the
order which evolution would necessarily proceed. Worth noting is the lack of any
real breach of sequence throughout the entire fossil record. If there were to be
such a breach it would throw much of the theory of evolution into question, but as
it is situated thus, evolutionary descent looks at worst probable. It seems much too
great a coincidence that these forms would follow this sequence. The idea that
environmental conditions caused changes in the groups present over time appears
as a very forced argument, although difficult to dispute decisively. This argument,
spear-headed by Lyell, is weak not so much by its own logic but in-so-far as the
separate creation theory which it supports has already been proven false. At the
end of these discussions, Ridley asserts that there is consequently “no sensible
alternative” to evolution, and that, insofar as whether or not evolution is true, the
answer is fairly clear.
From this extensive analysis of the necessity of evolution, a myriad of other
questions emerges, not least of which is the question which seeks the proper
relation of the evolutionary theory to the classification system. Ridley points out
that the strongest possible relation is one of practical necessity, one in which
evolution must precede the classification in order to give it structure. However, as
Ridley points out, this is simply not the case. History saw classification long
before the theory of evolution. The act of classification, after all, is a simple
process which merely requires its groups to be recognized, defined, and named
resulting in different traits defining different groups. However, a fundamental flaw
in classification is its tendency toward subjectivity; if classification was truly a
subjective practice alone, not only would evolution be practically unnecessary, it
would be completely unnecessary. The way to check this subjective germ in
classification is to classify with the aid of a perfectly unambiguous principle. In
this case no group would be chosen unless it is in reference to the principle. With
the introduction of this idea, Ridley asserts that evolution could fit into one of three
categories in relation to classification: 1) philosophically necessary, 2)
philosophically desirable, and 3) completely unnecessary. The hierarchy of
classification can be assumed; this means that one group will necessarily be
contained completely in more inclusive groups without overlap. According to
Ridley, two hierarchical principles exist. They are: 1) a phenetic hierarchy, one
which is governed by the similarity of form of the classified group, and 2) a
phylogenic hierarchy, one which is governed by the pattern of evolutionary
descent. Both principles may agree or disagree as is illustrated in Figure 2. In (a)
both agree in classification because the rate of evolution is approximately constant
in direction and divergent. This agreement is not present in the case of
convergence (b) or significant differential divergence (c).
Figure 2
Before beginning his discussion on both principles individually, Ridley
reminds the reader that if both principles are valid, evolution would merely be
philosophically desirable; if however, only the phylogenic principle is valid, then
evolution would be philosophically necessary. If however, both principles are
invalid, evolution would be completely unnecessary and classification would be a
completely and utterly subjective practice which bore no relation to evolution at
all.
Ridley begins his discussion of the phenetic principle by recalling the
difficulty of classification by an arbitrarily chosen trait. The phenetic principle, as
he points out, is much indebted to numerical taxonomy in order to compensate for
this arbitration. It classifies not by single traits, but as many traits as possible.
This is most handsomely illustrated by a certain statistic known as the multivariate
cluster statistic in which groups are defined by their overall morphological
similarity. The more traits used, the less arbitrary the arbitration. The statistical
clusters are formed by what has been termed as the „distance‟ between the units
being classified. This distance is the difference between the values of a trait in two
given groups. Because numerical taxonomy uses more than one trait, the distance
which forms the clusters is often a mean trait distance; it takes the sum of all trait
distances and divides the result by the number of traits. As such, the classification
of the phenetic principle is the hierarchical output of the statistical data. The
advantages which such a hierarchical output claims are objectivity and
repeatability, but, as Ridley explains, this claim is tainted. Drawing on the insight
of L. A. S. Johnson, Ridley explains how there can actually be more than one
cluster statistic for any set of traits because there is a plurality of ways in
recognizing the distance between groups. In other words, there is no principle
guiding which cluster statistics should be used. The principle of numerical
taxonomy provides no additional guidelines for the use of certain cluster statistics;
there is no way to differentiate a “better” cluster from a “worse” one. The decision
becomes one contingent on personal preference and therefore fails to live up to its
objective claim. The phenetic principle is in fact still a subjective approach to
classification.
In the failure of the phenetic principle, Ridley turns to phylogeny. What
makes the principle of phylogeny so refreshing is the observation that its hierarchy
exists independently of our techniques to measure it. The hierarchy is unique and
not pluralistic as with the phonetic principle. The criteria are more certain: there
either is either a common ancestor between two species or there is not; there is no
room for subjective choice. The immediate problem here is that it is impossible for
phylogenetic relations to be discovered by direct observation because evolution is
an historical phenomenon. Rather than discovered, they must be inferred. The
means of inference as proposed by Hennig is to seek traits which are “evolutionary
innovations.” This involves determining whether a given trait is an earlier or a
later evolutionary stage, a primitive or derived trait. Any given trait can be both
primitive and derived at once; with respect to later stage traits, it is primitive and
with respect to earlier traits, it is considered derived. One can also use a method
known as outgroup comparison which examines the state of some related species
known as the outgroup. In this method, the outgroup is a species no more closely
related to either of the two species being compared. Any trait found in the
outgroup would be considered primitive. It is not a foolproof method, as some
shared traits are due to convergence, but in most cases, shared traits are most often
due to common ancestry.
In each of the methods presented lies the fundamental problem that we need
to know the classification before applying the techniques, while it is the very
technique we must use to discover the classification. While this seems like a
paradox, Ridley suggests that it is simply the common practice of testing a theory.
An example of this hypothesis testing is exhibited in Figure 3 wherein the outgroup
comparison is used by successive approximation. In (a), five species are classified
together, and it is hypothesized that (6) is less related to them than they are to each
other. When trait A is compared in all six species, it is found that 2, 3, and 4 have
it in the form of “a” while species 1 and 5 have it in the form of “a‟”. Using the
method of outgroup comparison, we can reason that “a‟” is a derived state. Figure
3b has been adjusted to accommodate for this discovery. Now, species 1 and 5 are
classified together because of their shared derived “a‟” trait, and the relation s
between the other four species remain unknown until the procedure can be
repeated with new evidence of shared traits.
Figure 3
The method illustrated above employs what Ridley describes as “successive
approximation.” As the analysis develops, errors found in the original assumptions
are proven or disproven so as to minimize error along the way. With the
consequences of false assumptions removed, the classification moves closer and
closer to its most perfect form. In this way, classification is a classic case of
scientific theory-building. Rigorous adherence and alteration as a result of the
interpretation of facts constantly and consistently aids the accuracy of
classification. Despite the apparent perfection of the phylogeny principle, Ridley
makes is not satisfied with it as such. He insists its imperfections are manifold.
The first problem he points out is how to resolve conflicting information from
different traits. Despite this, Ridley illustrates that its imperfection does not render
it impractical. As he himself says, few biologists would deny the cladistic
evidence that humans share a more recent common ancestor with chimps than
butterflies. The other difficulties of phylogeny arise from the fact that traits
continually change in time and in place. This change is impossible to accurately
classify because classification itself strictly applies only to one place and not to
members from more than one geological period. Again, Ridley clarifies that this
problem is not one in practice but one in philosophy; it does not completely void
phylogeny‟s usefulness in classification.
Lastly, Ridley addresses the temptation one might feel to account phylogeny
as a form of phonetic classification. While there is some element of truth in that,
Ridley asserts that the represented hierarchy, not the techniques employed, are
what properly describe a classification system. While both phonetic and
phylogeny principles use shared traits as a technique, phylogeny‟s objective
principle is significantly better than the subjective quality of phonetic
classification. In the end, phylogeny has been aptly proven philosophically
preferable to its counterpart. Ridley answers his question as to the relation
between evolution and classification by asserting they are actually quite close, so
close indeed that it must be one of philosophical necessity. Herein lays a great
underlying irony: evolution is not practically necessary to classification, but it is
philosophically necessary. Ridley then proceeds to finish his work with a last
discussion on macro-evolution, what he considers the most open-ended question of
all the evolutionary theory. It is clear by the end of the work that despite the
necessity of evolution which he asserts in Chapter 1, “we lack evidence to support
an opinionated conclusion” (vi).
Ridley was a joy to read and a very stimulating writer. He has quite a skill
in the clarity of his words and in the communication of his ideas. Most of the
questions he asks are enough to make the reader reconsider his own position in
both extremes. Because of this, I find his book to be something of a hidden
treasure. I would recommend it to anyone seriously considering the controversy of
evolution, but I would also refrain from recommending it to anyone looking for
concrete answers as to the reality of evolution. Although it was scientifically
static, it was philosophically thrilling, and I am very glad to have read it.
Bibliography
Ridley, Mark. The Problems of Evolution. New York: Oxford University Press,
1985.