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.