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\tcrdate{31-Dec-1996}
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\title{Adaptation Considered Harmful:\\
Darwin's Problem Revisited}

\author{\htmlref{Barry McMullin}{mcmullin}\\
\htmlref{\copyright \thecopyrightdate}{copyright}}

\maketitle

\begin{quote}
\textbf{Keywords:} Darwinism, Adaptation, Artificial Life.
\end{quote}
\newpage
\vspace*{\fill}

\begin{abstract}

Evolutionary Epistemology---as formulated by D.T. Campbell and
Karl Popper---can be seen as a more or less explicit and
conscious attempt to \emph{generalise} Darwinian theory, in an effort to
solve the fundamental problem of epistemology: how can knowledge
grow?  I think we are entitled, therefore, to be at least a
\emph{little} concerned that Popper himself for a long time regarded
Darwinian theory as tautological and/or metaphysical; and
(worse?) that when he eventually recanted, he proceeded to
declare that Darwinism has, in fact, been refuted!

In an attempt to make sense of this situation, I here revisit
Darwin's original problem.  I will suggest that once this
\emph{problem} is properly understood, then the more common confusions
and misunderstandings associated with Darwin's \emph{solution} can be
satisfactorily resolved.  In particular, I make the modest
terminological proposal that the word \tcrquotes{adaptation} be forthwith
excised from the lexicon of evolutionary theory---it has done
a good deal more harm than good!

Finally, I will briefly consider the relevance to Darwin's
problem of some recent (purported) demonstrations of \tcrquotes{artificial}
Darwinian evolution, or \emph{Artificial Life}.

\end{abstract}

\vspace*{\fill}

\tableofcontents

\section{Prologue}

\tcrpar
The claim that Darwinism  is \emph{tautological} is 
an extremely hardy weed. It seems to sprout again, at
irregular, but fairly frequent, intervals; this, despite even the most
seemingly severe of critical commentary and dismissal (see, for example,
Dawkins \citeyear*{Dawkins:ExtendedPhenotype}, pp.~180--181, for a list).

\tcrpar
It is of course, a fundamentally Popperian notion that we are all
fallible, and mistakes will occur, and to that extent perhaps we should
not be surprised that the mistake of regarding Darwinism as tautological
should \emph{re}cur from time to time.  Nonetheless, I suggest that there
is at least a \emph{prima facie} case for thinking that the issue must go
a little deeper in this particular case. The very resilience of the
doctrine suggests that it can hardly be \emph{trivially}, or 
\emph{manifestly} mistaken. 
Furthermore, those who have propounded this
doctrine at various times seem, at the very least, to be otherwise
sensible and intelligent people.  I may mention Popper, of course, but
he himself has pointed out that he was influenced in this by a number of
other distinguished authorities \cite[p.~144]{Popper:EmergenceOfMind}.

\tcrpar
My problem then is to at least \emph{explain} the obstinate durability of
the thesis of Darwinian tautology; and perhaps, having explained and
understood this phenomenon, to mount a definitive critical attack on
the thesis.

\tcrpar
Thus, my objective here is not to persuade you that the tautological
view of Darwinism is mistaken---though, if you are in doubt, that
would be a beneficial side effect.  Rather, my objective is to convince
you that this thesis of Darwinian tautology is not \emph{trivially}
mistaken.  That, in fact, the thesis exists in a remarkable variety of
similar looking, but fundamentally distinct, forms.  As it happens,
these diverse forms require quite distinct criticisms; criticism that is
effective against one may be irrelevant to others.  My theory, if it
might be dignified with that term, is that it is this very diversity
that explains the historical difficulty of mounting a (single) decisive
criticism; for in the face of each such individual challenge the
doctrine can simply mutate into, or be displaced by, one of its
alternative forms that is resistant to that specific criticism.

\tcrpar
In short, what I propose to present here is the analog of a \tcrquotes{broad
spectrum antibiotic}, which will attempt to attack the thesis of
Darwinian tautology---and some closely related theses---in as
many of their variant forms as I possibly can.  I will not pretend to
you that this attempt at \emph{exhaustive} criticism can possibly be
stimulating or fascinating in itself; it is a tale of minute,
intricate, and very confusing detail.  Nor can I even hope to
definitively or permanently dispatch these theses---as Popper has
emphasised, even our criticisms are forever tentative and subject to
correction. Nonetheless, I will beg your indulgence for inflicting this
essay upon you, in the hope that by presenting the issues and arguments
as clearly and consistently as possible, I might at least offer the next
generation of would-be Darwinian tautologists a clear target to practise
against.

\section{Immutability and Common Descent}

\begin{quote}
  In considering the Origin of Species, it is quite conceivable
  that a naturalist, reflecting on the mutual affinities of
  organic beings, on their embryological relations, their
  geographical distribution, geological succession, and other
  such facts, might come to the conclusion that each species had
  not been independently created, but had descended, like
  varieties, from other species\ldots

  \citeasnoun[Introduction]{Darwin:TheOriginOfSpecies}
\end{quote}

\tcrpar Here, right at the start of \emph{The Origin} Darwin concisely
introduced, and immediately solved (or, at least, proposed a solution
to) a difficult biological problem---namely, why does the
biological world exhibit such hierarchical patterns of similarity, and
geological sequence, between distinct species of organisms?  There is,
of course, an historical context to this problem: the assumption that
species are immutable. Given this assumption, then these many relations
of similarity, at multiple hierarchical levels of classification, seem
arbitrary and thus problematic.  Conversely, if immutability is
discarded, then the problem situation is crucially changed, and we can
conjecture that most, or perhaps even all, organisms are bound by
relationships of common descent---and this very easily and naturally
explains the hierarchical pattern of similarity.

\tcrpar It is worth emphasizing that
Darwin did not \emph{originate\/} either this problem or its
solution---and nor did he claim to. As Burrow put it, in his
editor's introduction to a modern reprinting of {\it The
Origin\/}:
\begin{quote}
  The theory of evolution [i.e.\fsp of common descent] was already an old,
  even a discredited one.  Darwin, in later editions of {\it The
  Origin}, listed over thirty predecessors and was still accused of lack
  of generosity.

  \citeasnoun[p.~27]{Burrow:DarwinsOrigin}
\end{quote}

\tcrpar 
The theory of common descent can, of course, be challenged. For example,
its most ardent critics are the proponents of \tcrquotes{scientific
creationism}. However, for the purposes of this \emph{particular}
article, I am going to (tentatively) adopt the theory of common descent
as \emph{true}. I make this point explicitly at the outset, so that it
will clear in what follows that the problem I am dealing with is 
\emph{not} the 
problem of hierarchical biological \emph{similarity}, and should
not be confused with it.

\section{Darwin's Problem\label{dprob}}

\begin{quote}
  \ldots{} Nevertheless, such a conclusion [common descent], even if well
  founded, would be unsatisfactory, until it could be shown how
  the innumerable species inhabiting this world have been
  modified, so as to acquire that perfection of structure and
  coadaptation which most justly excites our admiration.

  \citeasnoun[Introduction]{Darwin:TheOriginOfSpecies}
\end{quote}

\tcrpar
With this continuation of the earlier quotation from Darwin
the problem situation is now extended, in
a crucial way. We arrive at what I shall term 
\emph{Darwin's Problem\/}:

\begin{description}
\item[\problem{d} (Darwin):] Given that species descend from other
species (i.e.\fsp given the theory of common descent), how is it that, in
some cases at least, this descent has been accompanied by an increase in
\emph{adaptive complexity}?

\end{description}

\tcrpar
I introduce (albeit with some hesitation) the term \emph{adaptive
complexity\/} here, following Maynard Smith:
\begin{quote}
  The main task of any theory of evolution ({\it sic\/}) is to
  explain adaptive complexity, i.e.\fsp to explain the same set of
  facts which Paley used as evidence of a Creator.  Thus if we
  look at an organism, we find that it is composed of organs
  which are at the same time of great complexity and of a kind
  which ensures the survival and/or reproduction of their
  possessor.  Evolution theory must explain the origin of such
  adaptations.

  \citeasnoun[p.~82]{MaynardSmith:StatusOfNeoDarwinism}

\end{quote}

\tcrpar
\citeasnoun{Popper:EmergenceOfMind} has similarly formulated a
version of \problem{d} by reference to Paley's famous \tcrquotes{argument from
design}---i.e.\fsp that the appearance of \tcrquotes{Design} in the
biological world \tcrquotes{proves} the pre-existence of a designer or
creator (which is to say, \emph{God\/}). Popper emphasizes that
Darwin himself acknowledged a strong influence from Paley's
formulation (and attempted solution) of this
problem.\footnote{At one point Popper explicitly calls this \tcrquotes{Paley's
  problem} (p.~345); but elsewhere in this same paper he refers to
  \tcrquotes{Paley's and Darwin's problem} (p.~342), which is thus consistent
  with my designation of \problem{d} as \tcrquotes{Darwin's Problem}.  I shall
  consistently use the latter name; partly because I have used Darwin's
  formulation, rather than Paley's, to introduce it; but mainly because
  there is a subtle difference between the problem as \emph{originally
  conceived\/} by Paley, and as \emph{actually solved\/} by Darwin. In my
  construction (\problem{d}), the (conjectured) truth of common descent is an
  explicit part of the problem situation; whereas, for Paley, the truth
  of common descent was neither a necessary part of (nor even
  particularly relevant to) the problem situation.}

\tcrpar Dawkins has adopted the terminology of
\tcrquotes{adaptive complexity} from Maynard Smith
\cite[p.~404]{Dawkins:UniversalDarwinism}, and I shall use this
phrase freely in what follows, but I shall also synonymously (?),
and sometimes preferentially, refer to \tcrquotes{inate} or
\tcrquotes{inborn} \emph{knowledge\/} in the sense introduced by
Popper:
\begin{quote}
  I assert that every animal is born with expectations or
  anticipations, which could be framed as hypotheses; a kind of
  hypothetical knowledge.  And I assert that we have, in this
  sense, some degree of inborn knowledge from which we may begin,
  even though it may be quite unreliable.  This inborn knowledge,
  these inborn expectations, will, if disappointed, create 
  \emph{our first problems\/}; 
  and the ensuing [somatic time] growth of
  our knowledge may therefore be described as consisting
  throughout of corrections and modifications of previous
  knowledge.

  \citeasnoun[pp.~258--259]{Popper:TreeOfKnowledge}
\end{quote}

\tcrpar 
\problem{d} refers to an increase or growth of adaptive complexity. I
thus implicitly assume some notion of \tcrquotes{degree} of adaptive
complexity; but I require only that this can be defined {\it a
posteriori}. That is, \emph{given} two organisms, I suppose that I
will, in general, be able to rank them (at least roughly) in terms of
relative adaptive complexity. I specifically eschew any attempt
to define an {\it a priori\/} measure of adaptive complexity.

\tcrpar
von~Neumann has described a similar idea as follows:
\begin{quote}
  There is a concept which will be quite useful here, of which we
  have a certain intuitive idea, but which is vague,
  unscientific, and imperfect \ldots{} I know no adequate name for
  it, but it is best described by calling it \tcrquotes{complication.}
  It is effectivity in complication, or the potentiality to do
  things.  I am not thinking about how involved the object is,
  but how involved its \emph{purposive operations\/} are.  In this
  sense, an object is of the highest degree of complexity if it
  can do very difficult and involved things.

  von Neumann\\
  (\citeyear*{vonNeumann:TSRAutomata} Fifth Lecture, p.~78, emphasis added)
\end{quote}

\tcrpar
Maynard Smith has similarly endorsed this somewhat loose
approach:
\begin{quote}

  At the outset we are faced with a difficulty: we have no way of
  measuring the degree of complexity of a structure.  Thus
  although most of us would readily agree that the organs of a
  man are more complex than those of an amoeba, and those of an
  amoeba more complex than those of a bacterium, we have no
  agreed criteria on which to base this decision, and no way of
  deciding by how much one organism is more complex than another.

  It may therefore seem odd to start formulating a theory of
  evolution by introducing a term which cannot be fully defined.
  However, I see no escape from doing so.  \emph{If organisms were
  not both complicated and adapted, living matter would not
  differ from dead matter, and evolution theory would have
  nothing to explain.}

  Maynard Smith\\
  (\citeyear*{MaynardSmith:StatusOfNeoDarwinism} pp.~82--83, emphasis added)

\end{quote}

\tcrpar
I consider that \problem{d} is the central, perhaps even the
defining, problem of evolutionary biology, and is the problem
Darwin hoped to solve with his theory of \emph{Natural
Selection}.\footnote{To this extent, the title of Darwin's book, 
  \emph{The Origin of Species} may be slightly misleading---it directs
  attention specifically at the phenomenon of \emph{speciation}, rather
  than at the growth of adaptive complexity.  While speciation is
  certainly an important issue we can say nonetheless that it is of
  secondary importance compared to the question of adaptive complexity.
  Diversity of species as such would be of relatively little interest if
  all species were equally rudimentary; conversely, even if there were
  only one species which displayed adaptive complexity, this one species
  would be of overwhelming interest. This is not, of course, to argue
  that speciation and the growth of adaptive complexity are 
  \emph{independent\/} phenomena, but 
  merely that I shall concentrate on the
  latter.}

\tcrpar
Before attempting to solve \problem{d} we must be clear as to how
\problem{d} goes beyond the basic problems of the hierarchical
relationships of similarity and geological ordering exhibited by
biological organisms; that is, in what respect(s) the theory of
common descent fails to address (much less solve) \problem{d}.

\tcrpar Briefly, while the theory of common descent
asserts the existence of a unique phylogenetic tree,
\problem{d} goes on to ask: why does the phylogenetic
tree has the particular structure that it has? Why,
above all else, does it display at least some cases of
increasing adaptive complexity?

\tcrpar
Note that the claim here is not that \emph{all\/} evolutionary
lineages have involved increasing adaptive complexity, but merely
that at least \emph{some\/} have. Similarly, even for those
evolutionary lineages where there has been a net increase of
adaptive complexity, there is no claim that this increase has
occurred at a steady rate, or that it has been monotonic, or (most
especially) that it will continue into the future.

\section{A Solution: Organismic Darwinism}

\tcrpar
It should not, perhaps, be necessary to burden the world with yet
another presentation of Darwinian theory.  Yet, insofar as the substance
of this article is concerned with alleged misunderstandings of this theory
it will be as well for me to present my own version---not least
because it may transpire, through criticism, that it is actually \emph{my}
version that is mistaken!

\tcrpar
Perhaps more importantly, I have spent some years struggling with
Darwinian theory, trying to ensure that I have grasped it fully.  I am
still not at all sure that I have succeeded; but I am satisfied that it
is a more complex, and subtle, theory that is generally admitted,
especially in the popular literature. This, in itself, persuades me to
attempt a fresh presentation.

\tcrpar 
I take the theory of \emph{Organismic\footnote{Attempts have, of course,
  been made to apply \tcrquotes{Darwinian} theory to a vast range of domains; I
  use the \tcrquotes{organismic} qualifier here simply to emphasise that I am
  talking about the application of Darwinism in its original context of
  the evolution of biological organisms. This usage is loosely related
  to the \emph{Organismic Evolution\/} of
  \citeasnoun{Beurton:OrganismicEvolution}, and the \emph{Organismic
  Selection\/} of \citeasnoun{Wright:GenicAndOrganismic}.}
Darwinism}, denoted \theory{d}, to involve a number of separate
theses, which I shall now describe in detail.


\subsection{Reproduction} 

\tcrpar
Individual organisms are typically capable of
reproduction, and in this way give rise to organism \emph{lineages}.

\subsection{Inheritance} 
\tcrpar Reproduction exhibits recurring patterns of
similarity (heritability) between parents and offspring. Certain
(sub-)lineages can thus be distinguished by reference to characteristics
which are preserved or propagated by inheritance within these
(sub-)lineages.

\tcrpar
Perhaps the best way of describing this notion of a lineage
distinguished by inheritance is as an example of a
\emph{self-producing} system: it is an instantiation of a set of
components collectively having just the property that they can
regenerate that same set.

\tcrpar
I shall refer to these special, inheritance-based, self-producing,
lineages as \emph{similarity-lineages} or \emph{S-lineages}.

\tcrpar
Note that, in general, lineages can, of course, be delimited in ways
\emph{other} than by reference to inherited characteristics---but
only the latter particular kind of lineage, namely S-lineages, will be
in question here. Note also that any given offspring of a parent
organism may or may not inherit any specified characteristics, and thus
may or may not belong to specific S-lineage(s) which the parent belongs
to.

\subsection{Selection} 

\tcrpar
Organism populations belonging to distinct,
inheritance-based, S-lineages can interact in a manner giving rise to a
\emph{quasi-deterministic selection dynamics}.  That is, an S-lineage
population can consistently grow, at the expense of one or more other
S-lineage populations, eventually displacing the latter completely.  An
S-lineage can thus be spontaneously and naturally \emph{selected} over
one or more other lineages.  I shall call this a \emph{(natural)
selection process}.

\tcrpar
Of course, lineages in general, and S-lineages in particular, may
participate in a very wide range of diverse ecological processes, most
of which do \emph{not} involve the quasi-deterministic elimination of one
or more or them.  Selection processes are, in this sense, only one
special case of a much more general phenomenon.  Nonetheless, selection
processes play a peculiarly important role in the Darwinian explanatory
schema, and must therefore be clearly separated out from all other
possible ecological interactions.

\tcrpar
Note carefully that the conditions under which such a selection process
will arise are highly variable, and difficult to characterise in
general.  Note, in particular, that not all lineages---not even all
S-lineages ---will necessarily be capable of participating in such a
selection process; and whether such a process arises will depend both
on the specific S-lineages present, and the extra-organismic
(\tcrquotes{environmental}) situation.

\tcrpar
It is worth noting in passing here that the observation that the entities
which get selected in Organismic Darwinism selection are a special kind of
\emph{lineage} (as opposed to individual organisms) is a major insight that
was only fully or properly recognised within the last 40
years. \citeasnoun[p.~ix]{Dawkins:NewSelfishGene} provides a brief
review of the genesis of this insight. It was originally formulated as the
theory of \tcrquotes{kin selection}, but has been more recently popularised by
Dawkins under the banner of the \tcrquotes{selfish gene}.\footnote{I find 
the latter term to be seriously confusing.  This is discussed 
at length in \cite{McMullin:GenicAndOrganismic}.}

\tcrpar
In circumstances where a selection process \emph{will} occur it is
generally possible to identify a numerical parameter, which can, in
principle, be \emph{independently} evaluated for each S-lineage involved,
such that the relative values of this parameter are predictive of the
ultimate outcome of selection (and, indeed, of the rate at which the
selective displacement will proceed).  The parameter will typically be a
function of expected fecundity and mortality in the given
conditions.

\tcrpar This numerical parameter is commonly referred to as
\emph{fitness}; however, like \tcrquotes{adaptation},
\tcrquotes{fitness} is a term which has had a variety of
ambiguous and conflicting meanings in the Darwinian literature,
so, for the moment at least, I would prefer to avoid it.  Instead
I shall adopt the relatively neutral term \emph{selective-value},
or \emph{S-value}.\footnote{The common \tcrquotes{S} prefixes in
  S-lineage and S-value are co-incidental, since they denote
  \tcrquotes{similarity} and \tcrquotes{selection} respectively;
  but since only S-lineages can have S-values, it is a convenient
  co-incidence; I did not intend it, but I am happy to allow it
  stand.}

\tcrpar
Note that S-value is not a property of an S-lineage as such: it is a
property of an S-lineage \emph{relative} to a particular selection
process---that is, relative to a particular set of other
S-lineages, with which it would interact, and relative to a particular
set of common environmental conditions.  The \emph{same} S-lineage could
be characterised by utterly different S-values relative to different
selection processes; and S-value would be literally \emph{undefined} on
sets of S-lineages which do not collectively generate selection
processes.\footnote{S-value is not even necessarily transitive. One
  could formulate S-lineages $A$, $B$, $C$, with properties such that
  all three distinct pairs would give rise to selection processes, where
  $A$ would reliably displace $B$, $B$ would reliably displace $C$, yet
  $C$ would reliably displace $A$!}
The common metaphor of Darwinian evolution as a process of hill-climbing
on a \tcrquotes{fitness landscape} is thus, at best, a highly dubious one.

\subsection{Variation} 

\tcrpar
New S-lineages are spontaneously formed, on an
ongoing basis, as \tcrquotes{variations} on pre-existing S-lineages.  In this
way, new selection processes arise, and episodes of selective
displacement occur, on an ongoing basis.

\tcrpar
Furthermore, the mechanisms of S-lineage variation are 
\emph{unjustified}---they are not mediated by knowledge or prediction of
the properties such variant S-lineages would exhibit. More specifically:
the S-value of a variant relative to any other S-lineages with which the
variant might interact in a selection process has no influence on
whether or not that variant will be generated in the first
place.\footnote{This thesis is commonly expressed by saying that
  variation is \tcrquotes{random}; but that term is very vague 
  and ambiguous.}\par

\subsection{Growth of Adaptive Complexity} 

\tcrpar Finally: in those phylogenetic lineages which have
exhibited significant growth of adaptive complexity, this has
arisen through sustained or repeated correlation between adaptive
complexity and S-value of S-lineages making up these phylogenetic
lineages. More specifically, where adaptive complexity has
grown, the increments in adaptive complexity have arisen as
unjustified variations in the properties of S-lineages, which
variant S-lineages have selectively displaced competing lineages
of less adaptive complexity, by virtue of their \emph{also}
having relatively greater S-value.  All long term growth of
adaptive complexity is composed of such events of unjustified
variation and selective retention.

\tcrpar
It is crucial to note here that this final thesis does \emph{not\/}
entail that adaptive complexity be \emph{always\/} correlated with
S-value, or (therefore) that adaptive complexity should 
\emph{necessarily\/} grow. Maynard Smith makes the point thus:
\begin{quote}

  There is nothing in neo-Darwinism which enables us to predict a
  long-term increase in complexity.  All one can say is that
  since the first living organisms were presumably very simple,
  then if any large change in complexity has occurred in any
  evolutionary lineage, it must have been in the direction of
  increasing complexity; as Thomas Hood might have said, `Nowhere
  to go but up'.  But why should there have been any striking
  change in complexity?  It is conceivable that the first living
  thing, although simple, was more complex than was strictly
  necessary to survive in the primitive soup, and that evolution
  of greater fitness meant the evolution of still simpler forms.

  \citeasnoun[pp.~88--89]{MaynardSmith:StatusOfNeoDarwinism}
\end{quote}

\tcrpar
That is, this theory solves \problem{d} only in the special sense that it
\emph{permits\/} a spontaneous growth of adaptive complexity; it
does not compel or predict such growth.

\tcrpar
This is an absolutely crucial point which is very rarely made explicit.
Instead it is commonly assumed, implicitly, that increased adaptive
complexity will just obviously or naturally involve increased S-value
(and will therefore be selected).  This is utterly mistaken, and leads
directly to the various tautology fallacies surrounding Darwinian
theory.

\subsection{Testing?}

\tcrpar I hope it is clear that each of these theses, which are
collectively claimed to compose \theory{d}, makes empirical
claims that are potentially testable: each of them could,
potentially, be mistaken.  Of course, actually carrying out
severe tests is difficult (to put it mildly). Popper put the
situation thus:

\begin{quote}
  \ldots Darwin's own most important contribution to the theory
  of evolution, his theory of natural selection, is difficult to
  test.  There are some tests, even some experimental tests; and
  in some cases, such as the famous phenomenon known as
  \tcrquotes{industrial melanism}, we can observe natural selection
  happening under our very eyes, as it were.  Nevertheless,
  really severe tests of the theory of natural selection are hard
  to come by, much more so than tests of otherwise comparable
  theories in physics or chemistry.

  \citeasnoun[p.~344]{Popper:EmergenceOfMind}
\end{quote}

\tcrpar
Nonetheless, for the purposes of \emph{this} article, I am concerned only
to show that the theory \emph{has} empirical content, and does---if
accepted---solve its problem (\problem{d}).  Thus, as with the theory of
common descent, I shall now (tentatively) adopt \theory{d}, the theory
of Organismic Darwinism, as \emph{true}.

\section{The Status of Organismic Darwinism}

\tcrpar
I have presented and analysed Organismic Darwinism as an essentially
straightforward theory---whose scientific status is not problematic.
However, this has not been a universally accepted position---and
this brings me to the central topic for this article.

\tcrpar
In fact, the status of Organismic Darwinism is a very vexing
question, which has received considerable attention in both the
biological and philosophical literature; the debate has
been positively acrimonious on occasion.

\tcrpar
I shall consider two closely related questions: whether Darwinism may be
a mere \emph{tautology}, or, failing that, whether it may be 
\emph{irrefutable\/} 
(and thus \emph{metaphysical\/}).  These two issues are
commonly conflated---for example by
\citeasnoun{MaynardSmith:StatusOfNeoDarwinism}. It is of course true that
all tautologies are untestable and therefore (in a trivial sense)
metaphysical, but the converse does not hold---theories may well be
metaphysical yet not tautologous. Thus, given that Darwinism is {\em
not\/} actually tautological then its testability becomes entirely moot,
and should be considered in its own right.

\subsection{Tautology\ldots}
\begin{quote}
  My dear Darwin,---I have been so repeatedly struck by the utter
  inability of numbers of intelligent persons to see clearly, or
  at all, the self-acting and necessary effects of Natural
  Selection, that I am led to conclude that the term itself, and
  your mode of illustrating it, however clear and beautiful to
  many of us, are yet not the best adapted to impress it on the
  general naturalist public \ldots{} I wish, therefore, to suggest
  to you the possibility of entirely avoiding this source of
  misconception in your great work (if not now too late), and
  also in any future editions of the `Origin', and I think it may
  be done without difficulty and very effectually by adopting
  Spencer's term (which he generally uses in preference to
  Natural Selection), viz. `Survival of the Fittest'.

  \citeasnoun{Wallace:Letter1866}\\{}
  [Quoted by Dawkins \citeyear{Dawkins:ExtendedPhenotype}, pp.~179--180]
\end{quote}

\tcrpar
I believe that the charge of tautology leveled against
Organismic Darwinism is quite mistaken.  However, contrary to,
for example,
\citeasnoun[pp.~180--181]{Dawkins:ExtendedPhenotype}, I also consider
that the confusion is deep seated and subtle.  In particular, I
believe that there are (at least) three quite different 
\emph{kinds\/} of misconception involved.

\tcrpar
There are a number of more or less authoritative replies to the
tautology charge already available in the literature (some of
which I shall comment upon below); but these have, in general,
only recognised one or another of the various possible
misconceptions. I am not aware of any previous discussion which
has clearly distinguished all three kinds of misconception which
I identify here.  I suggest that this may explain why this debate
has sometimes appeared interminable: the participants have
frequently been talking at cross purposes. In itself, this would
justify the somewhat lengthy discussion given here; but the
discussion is also justifiable in its own terms for it
illuminates some quite important aspects of Darwinian theory
which might not otherwise be explicitly dealt with.

\tcrpar
The discussion will (not surprisingly) be quite complex and
potentially confusing.  Therefore let me outline the general
structure in advance.

\tcrpar The arguments all revolve around Spencer's
unfortunate phrase \tcrquotes{the survival of the
  fittest}. I shall initially show how the phrase can
be interpreted as an (approximately) correct,
non-tautologous, (albeit \emph{partial}) statement of
\theory{d}---which is, presumably, the interpretation
Spencer intended. The first misconception which I
consider is such that the phrase is still
\tcrquotes{correctly} interpreted, but, in a certain
peculiar and austere sense, is labeled as tautologous
\emph{anyway}. Under the second misconception, there
are two distinct ways in which the phrase can more or
less correctly be interpreted as a \emph{definition\/}
of \tcrquotes{fitness}; both of these interpretations
are, of course, tautologous, but they are not
statements of \theory{d} and do not impinge upon its
status. Under the third (and final) misconception,
there is an interpretation of the phrase which is not
strictly tautologous, but is not equivalent to
\theory{d} (and is, in fact, mistaken). This last error
does involve an element of circular reasoning, and
might therefore be still said to \tcrquotes{smack} of
tautology; in many ways it is the most pernicious
misconception of all.

\tcrpar
In presenting this analysis I do not claim that my taxonomy is complete
or unique.  In practice, various combinations and permutations of the
errors identified below may well be simultaneously present in any single
author's treatment; and, of course, there may be new errors which I am
unwittingly originating, in carrying out this very analysis.

\subsubsection{On \tcrquotes{survival}}

\tcrpar
To analyse the arguments effectively, it is first necessary to
distinguish two quite separate notions of \tcrquotes{survival}:

\begin{itemize}
\item \textbf{\isurvival{}:} The survival of individual organisms.
\item \textbf{\lsurvival{}:} The survival of organism lineages (in
particular, S-lineages).
\end{itemize}

\tcrpar \isurvival{} obviously does not refer to
survival in any absolute sense: individual organisms
are essentially mortal, and have a finite lifetime---it
is hardly meaningful to speak of individual organisms
\tcrquotes{surviving} without
qualification.\footnote{Admittedly, it is a moot point
  whether this is true of \emph{unicellular} organisms;
  but I shall not pursue that further here.} However,
some organisms do survive \emph{longer\/} relative to
others.  More generally, there is potentially a valid
notion of \tcrquotes{mean \isurvival{}}---i.e.\fsp that a
certain \tcrquotes{kind} of organism may, in given
conditions, show a consistent distribution of values
for \isurvival{}. Furthermore, if (and only if) there
exist \emph{heritable\/} characteristic(s)
distinguishing such different \tcrquotes{kinds} then
they can serve to differentiate S-lineages. In that
case coherent S-lineages, exhibiting distinctive
(statistical) distributions of \isurvival{}, can be
formed. This distribution of \isurvival{} would be a
characteristic of an S-lineage. In fact, (mean)
\isurvival{} can then be thought of as a crude or
partial measure of S-value (crude because the latter
depends, at least, on fecundity as well as mortality);
in particular it will generally be true that the
greater the value of (mean) \isurvival{} then the
greater the S-value of the corresponding S-lineage.

\tcrpar I emphasize that (mean) \isurvival{} (as with
S-value proper) is defined as an objective
characteristic of an S-lineage in given conditions,
which can (in principle) be evaluated independently of
any prior knowledge of the \emph{outcome} of any
associated selection process.

\tcrpar \lsurvival{} \emph{does\/} (potentially) refer
to \tcrquotes{absolute} survival---in the sense that
organism lineages can (apparently) survive indefinitely
long.

\tcrpar
\lsurvival{} may also be related to S-value, but not in the relatively
direct way which holds for \isurvival{}. Let us suppose that, for 
\emph{independent\/} 
reasons, we believe that two S-lineages will give rise to
a selection process in specified conditions. Then we can infer that
whichever S-lineage is the eventual \lsurvivor{} must have the greater
value of S-value.  Note carefully that this inference is valid if and
only if we \emph{already\/} know that we are dealing with a selection
process.

\tcrpar
It should be clear that \isurvival{} and \lsurvival{} are not the same
thing.  While they \emph{may\/} be related this relationship is a
contingent one; it would not hold if, for example, among the organisms
being studied, there were no inheritable characteristics which were well
correlated with \isurvival{}; or if the S-lineages distinguished by
different values of (mean) \isurvival{} were not actually in competition
with each other etc.

\subsubsection{What Spencer Meant To Say?}

\tcrpar I suggest that the only correct interpretation
of Spencer's phrase (which is not \emph{necessarily\/}
the interpretation Spencer himself intended) is the
following: we interpret \tcrquotes{survival} as
\lsurvival{} (i.e.\fsp survival of \mbox{(S-)lineages);}
we interpret \tcrquotes{fitness} as \emph{S-value};
\tcrquotes{the survival of the fittest} is then at once
the assertion that:
\begin{itemize}
  
\item There exist lineages which may be distinguished
  by inheritable characteristics (S-lineages).\par

\item At least some of these S-lineages interact with
  each other in such a way as to give rise to a
  selection process.\par

\item The eventual outcome (\lsurvival{}) of this
  process is then quasi-deterministically related to
  the relative S-values (\tcrquotes{fitness}) of the
  participating S-lineages: hence \tcrquotes{survival
    of the fittest}.

\end{itemize}

\tcrpar As it stands this is essentially just a claim
that processes of natural selection do, in fact, take
place in the biological world. As such, it encompasses
just the \emph{inheritance} and \emph{selection} theses
of my \theory{d}.  It is then a correct, although very
incomplete, statement of \theory{d}. It is certainly
\emph{not} tautological.

\tcrpar
Again, it must be emphasized that this non-tautologous formulation
relies on the fact that S-value (fitness) is not \emph{defined\/} by
S-lineage \tcrquotes{survival}---rather it is, in principle, something that
can be assessed of an S-lineage isolated from the selection process, but
which is then \emph{predictive} of the outcome of that process.

\tcrpar
However, confusion might arise in cases where, for \emph{independent\/}
reasons, one \emph{already\/} believes that the displacement of one
S-lineage by another is, in fact, a case of selection: in that scenario
one can validly, and non-tautologically, infer that the surviving
S-lineage must have had the greater S-value.

\tcrpar
Essentially this (correct) interpretation has been commonly identified
in the literature---for example by Medawar (see
Moorhead \citeyear*{Moorhead:WistarSymposium}, p.~12), and
\citeasnoun[p.~58]{Hodge:DarwinsTheorizing}.

\subsubsection{Misconception 1: Logic}

\tcrpar
As detailed in the previous section, once the premises for
natural selection are granted (and this is an empirical question)
then the outcome---\tcrquotes{the survival of the fittest}---is assured.
That is, if we adopt these premises as \emph{axioms}, in the sense
of a formal logical system (i.e.\fsp they are taken to be \tcrquotes{true} by
definition), then \tcrquotes{the survival of the fittest} becomes a
theorem of the system, which is to say, in the strict terminology
of formal logic, a \emph{tautology}.

\tcrpar This is, of course, a technically valid point;
but it can hardly be called a \emph{criticism}. It
amounts to interpreting Spencer's phrase \emph{only\/}
as the (necessarily \tcrquotes{tautological})
conclusion of a certain deduction---rather than as an
implicit assertion of the truth of the premises which
lead to that conclusion. This is at best pedantic, at
worst misleading. It is equivalent to saying that
$E=mc^2$ (say) is a tautology---given the relevant
properties of $E$, $m$ and $c$. As Maynard Smith has
put it,
\begin{quote}
  Of course Darwinism contains tautological features: any
  scientific theory containing two lines of algebra does so\ldots

  \citeasnoun[p.~85]{MaynardSmith:StatusOfNeoDarwinism}
\end{quote}

\tcrpar
This is such a peculiar misconception that it seems difficult to
believe that it should genuinely arise. In practise I suggest
that it does not normally arise in isolation, but may be
combined with one of the other distinct misconceptions yet to be
described.  Having said that, there \emph{is\/} at least one case
where this misconception seems to have been uniquely involved:
\begin{quote}
  The notion of natural selection depends on the empirically
  verifiable observation that offspring on the average resemble
  their parents more closely than they do the other members of
  the population, that individuals are not all the same; that all
  environments are not the same.  Concepts such as natural
  selection by the survival of the fittest are tautologous; that
  is, they simply restate the fact that only the properties of
  organisms which survive to produce offspring, or to produce
  more offspring than their cohorts, will appear in succeeding
  generations.

  \citeasnoun[p.~5]{Eden:Inadequacies}
\end{quote}

Eden does seem to use the correct
interpretation of Spencer's phrase (notwithstanding the
fact that he immediately goes on to use
\tcrquotes{survive} in the sense of \isurvival{} rather
than \lsurvival{}); but insofar as he describes it as a
tautology he merely seems to mean that \emph{any\/}
valid deduction (\tcrquotes{restatement}) from true
premises is a \tcrquotes{tautology}.  While formally
correct, the observation does not add anything except,
possibly, confusion.

\tcrpar
Consider also, the following comment from Dawkins:
\begin{quote}
  Biologists thought they needed a word for that hypothetical
  quantity that tends to be maximized as a result of natural
  selection.  They could have chosen `selective potential', or
  `survivability', or `W' but in fact they lit upon `fitness'.
  They did the equivalent of recognizing that the definition they
  were seeking must be `whatever it takes to make the survival of
  the fittest into a tautology'.  They redefined fitness
  accordingly.

  \citeasnoun[pp.~181--182]{Dawkins:ExtendedPhenotype}
\end{quote}

I suggest that what Dawkins means here is that
fitness can be (indeed has been) defined as whatever it
takes to make \tcrquotes{the \lsurvival{} of the
  fittest} into a logical consequence of the existence
of heritable fitness variations and competition. I
should emphasize that, in context, Dawkins is
\emph{not\/} suggesting that this \tcrquotes{tautology}
can be translated into any \emph{criticism\/} of
Darwinism; but, as with Eden's version, I still find
the reference to \tcrquotes{tautology} to be confusing
and gratuitous.

\subsubsection{Misconception 2: Words\label{misconception2}}

\tcrpar Spencer's phrase does reduce strictly to a tautology if
\tcrquotes{fitness} is equated with \tcrquotes{survival}; that
is, the phrase is read as a \emph{definition\/} of fitness (and
definitions are, of course, a paradigmatic case of
tautology). This formulation of the tautology argument is the
most common; a good example would be that of
\citeasnoun[pp.~241--242]{Popper:CloudsAndClocks}.\footnote{However
note that Popper later repudiated this analysis, as I 
discuss in section~\ref{metaphysics}.}  As
Dawkins puts it, this kind of argument is \tcrquotes{a remarkable
example of the elevation of words above their station}
\cite[p.~181]{Dawkins:ExtendedPhenotype}.

\tcrpar
This misconception leads to tautology regardless of whether we
take \tcrquotes{survival} to mean \isurvival{} or \lsurvival{}.
Both cases are conceptually possible, although they have quite
different flavours.  In general, writers suffering from this
misconception are not clear about which sense they intend. In
fact, the most likely scenario may be a failure to distinguish
that there \emph{are\/} two possible, but distinct, strictly
tautologous interpretations---for if that fact is once
recognised, the possibility of a non-tautologous (and correct)
interpretation more or less immediately presents
itself.\footnote{There may be a lingering misconception that all
  tautologies are equivalent, so that the
  possibility of \tcrquotes{distinct} tautologies cannot arise; this is
  not the case. All tautologies have the same \emph{truth\/} value
  (namely, unconditionally \tcrquotes{true}), so that they are 
  \emph{logically\/} equivalent---but this is not at all the same
  thing. \tcrquotes{Cats are a kind of domesticated feline} 
  and \tcrquotes{$\pi$
  is the ratio of the circumference to the diameter of a circle}
  are ({\it qua\/} definitions) two \emph{different\/}
  tautologies.}

\tcrpar
The first distinct case of this misconception is this:

\begin{quote}
\textbf{Case 1:} \emph{the \isurvival{} of the \isurvivors{}}
\end{quote}

This amounts to defining fitness as (mean) \isurvival{}.

\tcrpar Now this interpretation is not
\tcrquotes{incorrect}. As already discussed above,
\isurvival{} is indeed a possible, though extremely
crude, measure of S-value; and \tcrquotes{fitness} can
be (and commonly is) interpreted as synonymous with
S-value.  So it is not entirely unreasonable to define
fitness as (mean) \isurvival{} (other things,
particularly fecundity, being equal).

\tcrpar
But of course, under this interpretation, the phrase is no longer
an expression of (the theory of) natural selection---it
is merely a preliminary definition.  Pointing out its
tautologous nature cannot impinge at all on the status of
\theory{d}.

\tcrpar The remaining variant on this misconception is:

\begin{quote}
\textbf{Case 2:} \emph{the \lsurvival{} of the \lsurvivors{}}
\end{quote}

This amounts to defining fitness as \lsurvival{}.

\tcrpar Unlike case~1, this is hardly even a coherent
definition.  Since \lsurvival{} is (at any given time)
a binary valued quantity, it is at least peculiar to
equate it with \tcrquotes{fitness} which, on any common
sense interpretation, should be continuous valued.

\tcrpar But let us stretch this point, for the time
being. We \emph{could\/} consider the phrase as
equating fitness with \lsurvival{}, \emph{regardless of
  whether natural selection is known to be
  operational}. But, as far as I am aware, this would
be a usage of \tcrquotes{fitness} which has never been
seriously proposed, is counterintuitive, and would be
of no apparent utility.

\tcrpar
This leaves only the possibility that we consider the phrase as a
definition of fitness \emph{only in cases where we have prior,
independent, knowledge of the operation of natural selection.}

\tcrpar Well, in this case we cannot say it is
positively incorrect---the operation of selection
guarantees precisely that \lsurvival{} \emph{will\/} be
related to S-value (the \tcrquotes{normal} meaning of
fitness), as already discussed for the correct,
non-tautologous, interpretation of Spencer's phrase.
At this point we are back to a similar situation to
that obtaining with Case~1: the interpretation can
\tcrquotes{reasonably} be adopted, but it is no longer
an expression of (the theory of) natural selection---it
is merely a preliminary definition (and a rather
confusing one at that).  Adopting this definition, we
would then have to introduce some additional term other
than fitness (S-value perhaps?), whose definition would
\emph{not\/} be already contingent on the outcome of
selection, before we could even formulate \theory{d}
properly.  But, in any case, we again conclude that
pointing out the tautologous nature of this
interpretation cannot impinge at all on the status of
\theory{d}.

\newpage
\subsubsection{Misconception 3: Adaptation\label{misconception3}}

\tcrpar The final misconception which arises does not
strictly involve a tautology, and is only incidentally
inspired or supported by Spencer's phrase.  However, it
does involve a degree of \tcrquotes{circular}
reasoning, is sometimes \emph{said\/} to be
tautologous, and is commonly associated with the
strictly tautologous misconception(s) of the previous
section.  It is therefore appropriate to consider it
here.

\tcrpar I consider this misconception to be the most
significant and pernicious of all, and will discuss it
in some detail.

\tcrpar I shall present the \tcrquotes{argument} in
what I consider to be its plainest form, but caution
that it is rarely if ever expressed in such explicit
terms.

\begin{itemize}
\item \theory{d} is proposed as a solution of
\problem{d}---i.e.\fsp as an explanation for the growth of
adaptive complexity in the phylogenetic tree.\par

\item For \theory{d} to successfully solve \problem{d} would require
that it \emph{predict\/} (stochastically or otherwise) the growth
of adaptive complexity.\par

\item At best, the only thing that \theory{d} actually predicts is a
growth of S-value in certain lineages.\par

\item Thus \theory{d} can be said to solve
\problem{d} only by \mbox{(re-)defining} adaptive
complexity to be the same as S-value (fitness).  This
effectively uses a circular definition, which is just
such that the problem to be solved (originally
\problem{d}) becomes simply \tcrquotes{whatever problem
  \emph{can\/} be solved (by \theory{d})}.
\end{itemize}

\tcrpar 
Arguments of this sort are tacitly involved
whenever there is a debate about the relationship
between \tcrquotes{fitness} and \tcrquotes{adaptation}.
Darwinism is first taken to be a theory of the growth
of \tcrquotes{adaptation} (informally conceived of in
terms of adaptive \emph{complexity}, or
\tcrquotes{fit} between organism and
environment---which is to say \emph{knowledge}); but it
is then noticed that Darwinism {\it per se\/} can
actually only explain the growth of \tcrquotes{fitness}
(in the sense of S-value); so it seems that it can work
as an explanation only if adaptation is
\emph{defined\/} as equivalent to fitness (and we
forget our original informal notion of adaptive
complexity, or adaptation to an environment).  This
does not turn Darwinism into a tautology in any strict
sense (though it does involve a kind of circularity);
but if this step is taken then Darwinism loses its
ability to solve the kind of problem we were originally
interested in---for the terms of the problem no longer
appear in the theory. It is thus greatly diminished in
scope and significance.

\tcrpar
Popper raised essentially this problem in what was (as far as I
am aware) his earliest consideration of the status of Organismic
Darwinism---his Herbert Spencer lecture, \emph{Evolution and the
Tree of Knowledge\/}:
\begin{quote}
  \ldots{} survival, or success in the sense of an increase in
  numbers, may be due to either of two distinguishable
  circumstances.  A species may succeed or prosper because it has
  managed, say, to improve its speed, or its teeth, or its skill,
  or its intelligence; or it may succeed or prosper merely
  because it has managed to increase its fecundity.  It is clear
  that a sufficient increase in fecundity depending fundamentally
  on genetical factors, or a shortening of the period of
  immaturity, may have the same survival value as, or even a
  greater survival value than, say, an increase in skill or in
  intelligence.

  \ldots{} But be this as it may, it should be possible, I think,
  to [measure] the \textit{success in the adaptation of the
  individual organisms\/} of a species \ldots

  Without some distinction such as this \ldots{} we are liable to
  lose sight of the original problems of Lamarck and Darwin, and
  especially of the explanatory power of Darwin's theory \ldots

  \citeasnoun[pp.~271--272]{Popper:TreeOfKnowledge}
\end{quote}

\tcrpar Popper is essentially pointing out that the temptation to
equate adaptation (or adaptive complexity) with fitness (or
S-value) must be resisted at all costs, for otherwise we lose
contact with the problems we wish to
solve. \citeasnoun{Lewontin:Adaptation} has discussed this
problem in very similar terms. Hull has also recently made much
the same point, concluding that the requirement to identify
adaptive complexity (which he actually calls
\tcrquotes{fitness}!) independently of S-value (which he terms
\tcrquotes{differential perpetuation}) cannot be circumvented
\tcrquotes{without evolutionary theory degenerating into an
empirically empty formalism}
\cite[pp.~318--319]{Hull:IndividualityAndSelection}.

\tcrpar
Now I have, indeed, been careful not to define adaptive
complexity in terms of S-value (or fitness).  Granted, I have not
attempted any formal or detailed definition of adaptive
complexity; and I have particularly eschewed any attempt to
establish a metric for it. But, as already discussed in
section~\ref{dprob}, this vagueness is not untypical in the
field; and I would argue that my general formulation in terms of
\emph{inborn knowledge\/}
\cite[pp.~258--259]{Popper:TreeOfKnowledge}
is still a more definite ontological commitment than is usual.

\tcrpar
It must be repeated that misconception~3 does not strictly
involve a tautology.  It is in this light that we must read
\possessivecite[p.~58]{Hodge:DarwinsTheorizing} claim that it is
\tcrquotes{a mistake to defend natural selection against the tautology
objection by proposing criteria of fitness independent of
reproductive success}.  I suggest that Hodge is here referring
only to the \emph{strictly\/} tautologous arguments already
discussed (particularly the two cases of misconception~2), and
\emph{not\/} to misconception~3, which has quite a separate
character. \citeasnoun[p.~10]{Dunbar:Tautology}, on the other
hand, \emph{rejects\/} the argument that \theory{d} cannot be
tautological because it is empirically testable (i.e.\fsp the kind
of argument offered by Hodge), saying that \tcrquotes{this claim misses
the point entirely}. I contend that Dunbar is effectively taking
up a position precisely complementary to that of Hodge, confining
his attention exclusively to misconception~3 and ignoring or
dismissing misconceptions~1 and/or~2. My position is that,
despite the apparent contradiction between Hodge and Dunbar, they
are actually both correct, so far as they go---but they are
discussing different problems (I consider Dunbar's analysis
in more detail in paragraph~\ref{dunbar}).

\tcrpar
At this point my argument is that misconception~3 is mistaken in
concluding that adaptation or adaptive complexity should, or
must, be defined in terms of S-value (fitness). I therefore
insist on retaining essentially independent definitions of
adaptive complexity and fitness (and thus retain \problem{d} in its
interesting form). What then are we to make of the original
criticism---that \theory{d} cannot actually solve this problem, for
it does not predict the growth of adaptive complexity
(so-defined)?

\tcrpar This brings us to the nub of the problem, which is to ask
how much we can sensibly ask of a proposed solution of
\problem{d}.  It seems to me that the error lies precisely in
supposing that a solution must (or even can) take the form of
some general theory which predicts a growth in adaptive
complexity. This derives in part from a fundamental
misunderstanding of what \problem{d} actually says.  \problem{d}
recognises that there has been a sustained growth in adaptive
complexity, in at least some evolutionary lineages, and asks for
an explanation of how this could be (preferably one which does
not assume the pre-existence of an even more complex creator). It
does \emph{not\/} say that growth in adaptive complexity
\emph{must\/} occur (in general or in particular lineages); or
that it had to occur in the particular way which it did; or that
it must continue occurring.  \emph{But only the latter kinds of
problem would call for a solution which incorporates a general
prediction of growth of adaptive complexity.}

\tcrpar We might characterise the general difficulty here as a
supposition that \problem{d} entails some kind of guaranteed,
monotonic, \tcrquotes{progress} (in adaptive complexity). It is a
harking back to the \tcrquotes{great chain of being}.  As Gould
puts it: \tcrquotes{The familiar iconographies of evolution are
all directed---sometimes crudely, sometimes subtly---toward
reinforcing a comfortable view of human inevitability and
superiority} \cite[p.~28]{Gould:WonderfulLife}. The idea of
necessary progress in evolution is so deeply entrenched that it
is very difficult to free oneself of it. Not even Darwin himself
was completely immune.  Although he explicitly emphasized that
the \emph{absence\/} of \tcrquotes{perfection} in biological
organisms should be interpreted as positive evidence in favour of
the operation of natural selection (at least as compared with a
theistic theory), we still find him remarking, in the concluding
pages of \emph{The Origin}, that \tcrquotes{\ldots{} as natural
selection works solely by and for the good of each being,
\emph{all corporeal and mental endowments will tend to progress
towards perfection\/}} \cite[Chapter~XIV, emphasis
added]{Darwin:TheOriginOfSpecies}.\footnote{See
\cite[Essay~4]{Gould:EverSinceDarwin} for a more detailed
discussion of whether Darwin \tcrquotes{really} endorsed the idea
of necessary progress in evolution.}

\tcrpar Once, however, we free ourselves from the
preconception that organismic evolution is a story of
necessary or inevitable \tcrquotes{progress}---and
excise this idea from \problem{d}---then the way is
open to consider \theory{d} as offering at least a
partial solution.

\tcrpar Briefly, as has been commented upon several
times, \theory{d} cannot and does not predict the
growth of adaptive complexity.  However, given that
adaptive complexity \emph{has\/} grown, \theory{d} can
retrospectively offer a generalised explanation for
it---namely that the growth of adaptive complexity
\tcrquotes{happens} to have been correlated with the
growth of S-value---and, crucially, \theory{d} can do
this without postulating the existence of any
\tcrquotes{designer} (prior knowledge) directing the
overall course of evolution.

\tcrpar \theory{d} in itself, does not explain why
adaptive complexity should be correlated with S-value
either in general, or in any particular case; not does
it explain how (heritable) adaptive complexity can
increase at all, in general or in any particular case.
In addressing \problem{d} it \emph{does\/} entail that
some (heritable) increases in adaptive complexity have
occurred, and that, of these, at least some have been
correlated with S-value; but it specifically
\emph{denies} that such increases in adaptive
complexity have been \tcrquotes{designed} or
\tcrquotes{anticipated}, or that they have been
\emph{universally\/} correlated with S-value.

\tcrpar Now, of course, \theory{d} \emph{does\/}
predict more or less monotonic \tcrquotes{progress} in
one very specialised sense: increase in S-value (within
some lineages).  But that much is true of all systems
where (S-lineage) selection processes arise, and does
not impinge at all on the central problem of the growth
of adaptive complexity.  No doubt we can conduct a
certain amount of evolutionary theorizing without ever
referring to adaptive complexity: but we can certainly
never solve \problem{d}. The crucial extra step, which
is rarely made explicit is to say that, given
\theory{d}, adaptive complexity can grow in
evolutionary lineages if and only if at least some
(\tcrquotes{unjustified}) increases in adaptive
complexity occur, and, of these, at least some are
correlated with a net increase in S-value (i.e.\fsp are
selectively retained).

\newpage
\tcrpar Of course, the reasoning given here only works
at all if it is accepted that an increase in adaptive
complexity \emph{might\/} be correlated with greater
S-value.  If I had defined adaptive complexity in some
(strange) way which was intrinsically opposed to
S-value (say, necessarily involving unconditional
altruism on the part of the S-lineage) then the
argument could not go through.  But my actual
definition---which corresponds to something like
\tcrquotes{inate knowledge}---does precisely have the
characteristic that, {\it ceteris paribus}, it may be
expected to be correlated with higher S-values.  But
the {\it ceteris paribus\/} clause is absolutely
crucial here; to ignore or omit it would effectively
mean a reversion to equating adaptive complexity with
S-value, and thus defining away the real problem.

\tcrpar None of this is to say that the growth of
adaptive complexity cannot be explained (or even
predicted); it simply claims that there cannot be any
\emph{general\/} theory of it (as always, this is just
another way of denying the existence of a logic of
induction).  \theory{d} asserts precisely that, for all
\emph{particular\/} historical cases of an increase in
adaptive complexity, there is a \emph{particular\/}
explanation, involving an \tcrquotes{unjustified}
variation in adaptive complexity (which happened to be
an increase) which was selectively favoured. It may or
may not be possible to organise these particular,
historical, explanations into a smaller number of more
general cases: but I take the view that it will not be
possible to translate these particular explanations,
nor generalisations of them, into predictions for
continuing growth of adaptive complexity into the
future. The aggregation of all the particular cases (if
such could be individually established) would then be
the complete (historical) \tcrquotes{explanation} of
all growth of adaptive complexity in the biological
world. But \theory{d} does not assert that such growth
had to occur, nor that it will continue into the
future, nor even that it would necessarily recur on
another \tcrquotes{similar} planet.

\tcrpar The confusions and misconceptions discussed here have
centred on the distinction between \tcrquotes{adaptation} and
\tcrquotes{fitness}.  For this reason I have tried to avoid these
terms in my own general presentation of Darwinism: the only
lingering remnant is the \tcrquotes{adaptive} in
\tcrquotes{adaptive complexity}. I have retained this in
deference to the existing biological literature, but I suggest
that it might actually be better to eliminate even this
concession.  In speaking of the \tcrquotes{adaptation} of
biological organisms it seems almost impossible not to think in
terms specifically relating to their success in living and
procreating---which is to positively invite a reversion to the
relatively sterile concept of S-value.

\tcrpar \label{dunbar} A particularly \tcrquotes{good} example of this is
Dunbar's analysis \cite{Dunbar:Tautology}. He is very clear about
the \emph{need\/} to distinguish \tcrquotes{adaptation} and
\tcrquotes{fitness}.  Furthermore, he seems to adopt much the
same kind of distinction as I have suggested above, interpreting
adaptation in terms of \tcrquotes{problem-solving}
\cite[p.~11]{Dunbar:Tautology} (following Lewontin
\citeyear*{Lewontin:Adaptation}, among others).  He seems to
recognise the essential \emph{independence\/} of the two concepts
when he cites Dobzhansky (apparently favourably) as saying that
\tcrquotes{we cannot draw inferences about fitness from a
knowledge of adaptation, nor of adaptation from a knowledge of
fitness} \cite[p.~14]{Dunbar:Tautology}. However, he then goes on
to explicitly deal with the alleged circularity of Darwinian
explanations, in the following terms:
\begin{quote}
  The relationship between the concepts of adaptation and fitness
  might seem to confirm the worst fears of the anti-Darwinians.
  Each appears to depend on the other in a way which makes them
  virtually inseparable.  It is, however, crucial to appreciate
  that they are not {\it definitionally\/} interdependent:
  adaptation is not {\it defined\/} in terms of fitness, nor vice
  versa.  Adaptation (and hence reproductive success) is defined
  with reference to {\it individuals}, whereas fitness is defined
  with reference to genes and is thus a characteristic of
  populations.

  \cite[p.~16--17]{Dunbar:Tautology}
\end{quote}

Dunbar here seems to suggest that the distinction between
adaptation and fitness is (merely?) a distinction between
properties of organisms and (consequent) properties of
lineages. The best interpretation I can offer of this is as a
somewhat tortuous reference to what I have called misconception~2
above---effectively a failure to distinguish \isurvival{} and
\lsurvival{}. Having thus retreated from the real
issue---misconception~3---Dunbar finds that he must admit that a
significant circularity may still remain in Darwinian theory. It
is perhaps not surprising that he then resorts to the
philosophical relativism of Kuhn and Feyerabend as his final
defence of Darwinism against circularity. I, of course, take the
view that such a conclusion is unsatisfactory and
unnecessary---that the conceptual independence of fitness and
adaptation (S-value and adaptive complexity) can and should be
recognised, and this can be done without depriving Darwinism of
its power as an explanatory schema.  However, it does underline
the point that the terminology of \tcrquotes{fitness} and
\tcrquotes{adaptation} may be critically flawed.  Thus, if one
confines oneself to discussion in terms of (inate)
\emph{knowledge} instead of adaptation or adaptive complexity, it
may be easier to remember that there is no \emph{necessary\/}
connection between these things and their retention or growth
under natural selection.  It should then be clear that any
connection which may exist will have to be individually argued
for in each particular case.

\tcrpar In short, I propose that the term \tcrquotes{adaptation}
(and \tcrquotes{fitness} too, for that matter) be henceforth
considered harmful, and be avoided in formulating and presenting
the theory of Organismic Darwinism.

\subsection{\ldots{} or Metaphysics?\label{metaphysics}}

\tcrpar As with the idea that Darwinism may be tautological, the
assertion that it is essentially metaphysical has been more or
less independently suggested (and criticised) by a number of
different authors.

\tcrpar The criticism of the so-called
\emph{adaptationist programme\/} by Gould and Lewontin
is an example of this kind of argument
\cite[p.~589]{Gould:SpandrelsOfSanMarco}. Indeed,
Lewontin has explicitly claimed that \tcrquotes{the
  adaptationist programme makes of adaptation a
  metaphysical postulate, not only incapable of
  refutation, but necessarily confirmed by every
  observation} (Lewontin
\citeyear*{Lewontin:EncyclopediaEinaudi}, as quoted by
Maynard Smith \citeyear*{MaynardSmith:Optimization},
p.~38).

\tcrpar However, the claim put forward by Gould and
Lewontin is not strictly that Darwinism {\it per se\/}
is metaphysical.  Indeed, they accept the empirical
reality of natural selection; their argument is about
which evolutionary phenomena are explicable in terms of
selection.  The adaptationist programme, which they
criticise, presumes that \emph{all\/} evolutionary
phenomena (or organismic attributes) are a direct
outcome of selection.\footnote{In this respect, the
  term \tcrquotes{adaptationist} is unfortunate, as it
  invites a form of the tautology misconception~3;
  \tcrquotes{selectionist} might be less prejudicial.}
Conversely, it seems clear that Gould and Lewontin
accept that what I have called adaptative complexity,
where it exists, does demand an explanation in terms of
selection; and, while such explanations may,
individually, be almost impossible to test in practise,
they are testable in principle, and are not therefore
metaphysical. Thus, \emph{in terms of the problem of
  adaptative complexity (\problem{d}),\/} Gould and
Lewontin appear to accept that \theory{d} is not
metaphysical, and, indeed, that it is the best theory
currently available.

\tcrpar
Concerns of a similar sort to those raised by Gould and Lewontin
have been independently discussed by various other workers.  For
example, they were prominent in the discussions at the 
\emph{Wistar\/} symposium on \tcrquotes{Mathematical Challenges to the
neo-Darwinian Interpretation of Evolution}
\cite{Moorhead:WistarSymposium}.  Although Popper was not
present at this symposium, he was repeatedly cited (directly or
indirectly) as the source for such concerns.  Thus, for example,
Medawar makes the following comment in introducing the symposium:
\begin{quote}
  Then there are philosophical or methodological objections to
  evolutionary theory.  They have been very well voiced by
  Professor Karl Popper---that the current neo-Darwinian Theory
  has the methodological defect of explaining too much.  It is
  too difficult to imagine or envisage an evolutionary episode
  which could \emph{not\/} be explained by the formulae of
  neo-Darwinism.
\end{quote}

\tcrpar Unfortunately, there are no detailed citations
to original sources, and I am not aware of Popper ever
having published \emph{exactly\/} this criticism of
Darwinism.  In any case, my response to this argument
is essentially as already discussed in the case of
Gould and Lewontin: while \theory{d} is, undoubtedly,
difficult to test in respect of the evolution of
specific complex adaptations, it is still testable in
principle (i.e.\fsp is not metaphysical) and is the best
theory currently available.

\tcrpar However, Popper \emph{has\/} published a
slightly different argument for regarding Darwinism as
metaphysical---or, more precisely, as a
\emph{metaphysical research programme}
\cite[Section~37]{Popper:Autobiography}. This arose (at
least partly) because, as already noted
in section~\ref{misconception2},
Popper's earliest considerations of the status of
Darwinian theory suffered from a form of
misconception~2, and he felt that the theory was
therefore \tcrquotes{almost tautological}; yet he also
felt that, \emph{despite this,} the theory had
considerable explanatory power. Popper seems to have
thought that this apparent contradiction might be
resolved by regarding Darwinism as a metaphysical
research programme.  While I think his interpretation
of Darwinism as tautologous was mistaken, I actually
agree that, in a certain limited sense, it \emph{can\/}
usefully be regarded as metaphysical.

\tcrpar
Firstly, as discussed in \cite{McMullin:DarwinianOntology}, I
consider that it is not unreasonable to describe the 
\emph{abstract\/} form of Darwinian theory, presented in that essay,
as a metaphysical research programme in Popper's sense. It is not a
scientific theory until the primitive entities (especially
D-actors) are given some specific empirical interpretation.  It must be
emphasized that to view this admission (of the metaphysical
nature of the abstract theory) as a \emph{criticism\/} of any
particular interpretation of the theory (such as Organismic
Darwinism) would be to indulge again in a form of the tautology
misconception~1.  This, for example, is the only way in which I
can understand one of Peters' purported criticisms of Organismic
Darwinism \cite[p.~4]{Peters:Tautology}, which is apparently
based on its being a specific interpretation of the axiomatic
Darwinism of \citeasnoun{Williams:ConsequencesOfEvolution}.

\tcrpar
Having said that, it must be recognised that the abstract or
axiomatic form of Darwinism is metaphysical in a deeper or more
profound sense than the conventional abstract theories underlying
all science.  The general kind of problem which abstract
Darwinism seeks to solve is the growth of knowledge; and its
mechanism of solution entails a refusal to make predictions---it
\tcrquotes{works} (in the face of the impossibility of a logic of
induction) precisely by \emph{declining\/} to predict the growth
of knowledge.  This is a quite unique kind of abstract theory.
It follows that, \emph{even\/} when the abstract theory is
interpreted in specific empirical terms (such as in the form of
Organismic Darwinism) it can never predict the \emph{future\/}
growth of knowledge.  We must say that, as long as such a
particular interpretation of Darwinism is viewed as an 
\emph{historical\/} theory of the \emph{past\/} growth of knowledge it
is perfectly testable (in terms of \tcrquotes{retrodictions}) and
scientific; but if it is mistaken for a \tcrquotes{universal law} of the
growth of knowledge, then, since it cannot predict such growth,
it must be treated as metaphysical. The (metaphysical) position
adopted here is, of course, that no \tcrquotes{universal law}
of the growth of knowledge exists.

\tcrpar
It can be seen that this argument for viewing even Organismic
Darwinism (as opposed to Darwinism in the abstract) as metaphysical
hinges on its (in)ability to predict the future growth of
knowledge, or adaptive complexity; thus it is closely related to
what I have labeled tautology misconception~3.  This is brought
out clearly by considering Popper's most substantive
presentation of this viewpoint:
\begin{quote}
  \ldots assume that we find life on Mars consisting of exactly
  three species of bacteria with a genetic outfit similar to that
  of three terrestrial species.  Is [organismic] Darwinism
  refuted?  By no means.  We shall say that these three species
  were the only forms among the many mutants which were
  sufficiently well adjusted to survive.  And we shall say the
  same if there is only one species (or none).  Thus Darwinism
  does not really \emph{predict\/} the evolution of variety.  It
  therefore cannot really \emph{explain\/} it.  At best, it can
  predict the evolution of variety under \tcrquotes{favourable
  conditions}.  But it is hardly possible to describe in general
  terms what favourable conditions are---except that, in their
  presence, a variety of forms will emerge.
  
  And yet I believe I have taken the theory almost at
  its best---almost in its most testable form.  One
  might say that it \tcrquotes{almost predicts} a great
  variety of forms of life.  In other fields, its
  predictive or explanatory power is still more
  disappointing.  Take \tcrquotes{adaptation}.  At
  first sight natural selection appears to explain it,
  and in a way it does; but hardly in a scientific way.
  To say that a species now living is adapted to its
  environment is, in fact, almost tautological.  Indeed
  we use the terms \tcrquotes{adaptation} and
  \tcrquotes{selection} in such a way that we can say
  that, if a species were not adapted, it would have
  been eliminated by natural selection.  Similarly, if
  a species has been eliminated it must have been ill
  adapted to the conditions.  Adaptation or fitness is
  \emph{defined\/} by modern evolutionists as survival
  value, and can be measured by actual success in
  survival: there is hardly any possibility of testing
  a theory as feeble as this.

  \citeasnoun[pp.~136--137]{Popper:Autobiography}
\end{quote}

\newpage
\tcrpar As already mentioned, Popper had earlier
\cite{Popper:TreeOfKnowledge} recognised the danger of
misconception~3, and the consequent need to keep
adaptation and fitness (selection) clearly separated;
but in this later consideration of the problem he seems
to have decided that such separation cannot be
achieved. Viewed as a putative theory of the growth of
adaptive complexity (i.e.\fsp of the evolution of a
\tcrquotes{rich variety} of more or less
\tcrquotes{well adapted} forms), Darwinism then becomes
irrefutable (metaphysical), for, no matter how little
the variety or adaptation we observe, it \emph{could\/}
still result from Darwinian processes.

\tcrpar Clearly, I agree with the essence of Popper's
argument; the difference is that instead of discarding
Darwinism, I discard the idea that adaptation and
fitness be defined in terms of one another.  Granted,
Darwinism cannot then \tcrquotes{predict} the growth of
adaptation or adaptive complexity.  But, once
adaptation is interpreted in terms of
\emph{knowledge\/} this becomes precisely consistent
with Popper's general evolutionary epistemology, and is
seen as the strongest kind of theory we can expect.
And, as a theory of the \emph{historical\/} growth of
adaptive complexity in the biological world, it is
perfectly scientific.

\tcrpar I have expended some effort in considering
Popper's criticism of the scientific status of
Darwinism because I think it relates to some difficult
and important issues, which are relevant objectives of
this article as a whole. However, it must be added that
Popper himself subsequently modified his views
significantly \cite{Popper:EmergenceOfMind}.
In particular, Popper recognised and corrected
the error implicit in tautology misconception~2, and
accepted that (Organismic) Darwinism can be so
formulated that it is definitely not tautologous.
Unfortunately, he then goes on to say that, in such a
form, it is literally false (has been refuted).  At
first sight this is an even worse accusation than the
original assertion that the theory was (almost)
tautologous and/or metaphysical.  However, Popper's
reformulation is the strong one that \emph{all\/}
aspects of the phylogenetic tree are the outcome of
cumulative natural selection; such a strong claim,
which is essentially equivalent to the adaptationist
programme criticised by Gould and Lewontin, is, indeed,
false. Popper does not explicitly consider the lesser
(but still non-tautologous) claim that all instances of
the growth of adaptive complexity (i.e.\fsp my
\problem{d}) are the outcome of cumulative natural
selection (i.e.\fsp my \theory{d}), and certainly does not
argue that \emph{this\/} formulation has been refuted;
so there is, in fact, no conflict with the views I have
expressed.

\tcrpar In conclusion, let me reiterate that I consider
\theory{d}, viewed as an historical theory of the
growth of adaptive, organismic, complexity, to qualify
as a good scientific theory--- \emph{despite\/} the
fact that actually testing it in specific cases is
enormously difficult. More specifically, \theory{d}
qualifies as scientific according to \emph{Popper's\/}
criteria.  I emphasize this last point because, even
though Popper might be called a \tcrquotes{\naive}
falsificationist with respect to the \emph{logic\/} of
(scientific) theories, he has always been a critical
falsificationist with respect to the
\emph{methodology\/} of actually carrying out
scientific research. This point has, apparently, been
commonly misunderstood or misrepresented (Magee
\citeyear*{Magee:Popper}, pp.~23--24; Popper
\citeyear*{Popper:Replies}, pp.~981--984). The
relevance of the distinction here is that it can be a
perfectly consistent Popperian position to assert that
Darwinism is scientific by virtue of its (logical)
falsifiability, \emph{even\/} if such falsifiability is
\emph{methodologically\/} almost impossible to exploit
(i.e.\fsp tests which could falsify the theory may be
perfectly conceivable, yet wholly impractical).

\section{Epilogue: Artificial Life}

\begin{quote}
  \ldots{} I do not really believe that we shall succeed
  in creating life artificially; but after having
  reached the moon and landed a spaceship or two on
  Mars, I realize that this disbelief of mine means
  very little.  But computers are totally different
  from brains, whose function is not primarily to
  compute but to guide and balance an organism and help
  it to stay alive.  It is for this reason that the
  first step of nature toward an intelligent mind was
  the creation of life, and I think that should we
  artificially create an intelligent mind, we would
  have to follow the same path.

  \citeasnoun{Popper:SelfAndItsBrain}

\end{quote}

\tcrpar My interest in Darwinian theory stems from
attempts to realise something like a spontaneous growth
of knowledge, by Darwinian means, in \emph{artificial}
systems---a problem which is now generally captured
under the rubric of \emph{Artificial Life}
\cite{Langton:ALifeDefinition}. I may note in passing
that, as the quotation above indicates, Popper deserves
to be recognised as at least one of the founders of
this field; indeed, as early as 1961, in his Herbert
Spencer lecture \emph{Evolution and the Tree of Life},
Popper presented a moderately elaborate, if schematic,
discussion of the possible evolutionary growth of
knowledge of a strictly artificial (robotic) system
\cite{Popper:TreeOfKnowledge}.

\tcrpar So, in this epilogue I would like to briefly
wave my hands in the direction of some recent work in
Alife, and the problems considered in the article.

\tcrpar First, let me note that any attempt to realise
the growth of adaptive complexity, via (genuinely)
Darwinian processes, in artificial systems, could, in
itself, represent a further kind of \emph{test} of
\theory{d}.  While such tests could hardly provide a
strong \emph{refutation\/} of \theory{d} (due to the
necessarily limited scale of artificial systems
compared to biological evolution) the
\emph{successful\/} demonstration of significant,
spontaneous, growth in adaptive complexity in
artificial systems, were it to be achieved, might still
represent a significant \emph{corroboration\/} for
\theory{d}.

\tcrpar I hasten to add that I do not consider that the
achievements to date in this direction should be
overrated---but there are some intriguing straws in the
wind, at least.

\tcrpar Among the best known efforts in this direction
are the \emph{BioMorphs} of Richard Dawkins
\citeyear{Dawkins:BlindWatchmaker} and the
\emph{Tierra} system of Tom Ray
\citeyear{Ray:SynthesisOfLife}.  However, the
\emph{BioMorphs} system is limited to static (albeit
very \tcrquotes{lifelike}) \emph{images} of artificial
\tcrquotes{organisms}; and while \emph{Tierra} does
involve \emph{dynamic} entities (fragments of computer
code) their environment is so alien to our normal
experience that it is very difficult to assess whether
\tcrquotes{knowledge}, in anything like its Popperian
sense, is being created or discovered.

\tcrpar In my view then, the most impressive work of
this sort to date is that on evolving
\tcrquotes{virtual creatures} by Karl Sims
\cite{Sims:EvolvingVirtualCreatures,Sims:EvolvingMorphology}.
Sims first constructed a \tcrquotes{virtual}
(computational) environment which reasonably faithfully
models normal, three dimensional, Newtonian
space---optionally including a viscous medium and/or a
uniform gravitational field.  He was able to embed
within this environment virtual or simulated creatures.
These creatures are \tcrquotes{grown} from
\tcrquotes{genetic} \emph{descriptions}. They consist
of roughly cuboid components, of various sizes, jointed
together in various ways, and controlled by a
distributed artificial \tcrquotes{nervous system}.
Starting from randomised descriptions, and using
artificial selection (i.e.\fsp controlled by a
predetermined \tcrquotes{fitness function}) Sims has
been able to demonstrate the spontaneous evolution of
creatures exhibiting swimming, walking, and jumping
behaviours; creatures which can track an environmental
stimulus; and creatures which can compete (in very
stylized combat rituals) for possession of
\tcrquotes{resources}.

\tcrpar Furthermore, in achieving these behaviours,
many of Sims' creatures exhibit morphologies and
organisation that would undoubtedly be called
\tcrquotes{adaptations} if found in biological
organisms.  I suggest that there is at least a {\it
  prima facie\/} case for claiming that these creatures
have spontaneously acquired significant
\emph{knowledge} of their world; that this growth of
knowledge was by fundamentally Darwinian means; and
that this lends some degree of independent
corroboration to conventional, biological, Darwinism.
At the very least, I suggest that this work
demonstrates that there is more to Darwinism than a
tautology!

\tcrpar Having said that, there are also limitations in
this work.  For example, reproduction and development
do not take place within the virtual environment, thus
limiting the opportunities for anything like somatic
time learning.

\tcrpar But, more importantly I think, selection is
driven by a predefined, and externally imposed,
evaluation function. I suggest that, for this reason,
evolution in this system may be effectively limited to
the refinement of what
\citeasnoun[p.~275]{Popper:TreeOfKnowledge} called the
\emph{skill-structure} of the creature.  The higher
level \emph{aim-structure} is effectively determined by
the imposed evaluation function (as \tcrquotes{walk},
or \tcrquotes{swim}, or \tcrquotes{fight} etc.).
Popper conjectured that mutations in the
\emph{aim-structure} might, in the biological world,
explain certain very significant long term phylogenetic
trends.  In my terms, this seems to offer something
like a mechanism for a long term correlation between
knowledge and S-value---which is to say, a potential
explanation for major episodes of Darwinian growth of
knowledge. But it seems to me that, for the moment,
this possibility is effectively closed off in Sims'
system.

\tcrpar The central difficulty in all of this is, of
course, that the empirical phenomena with which
\theory{d} deals are of such a scale in both time and
space that they are very difficult to subject to any
severe test, even via computer simulations.  I remain
convinced that \theory{d} is, in principle, testable;
but I will leave the last word with Popper again:

\begin{quote}
  
  \ldots{} we have to add that the phrase {\it in
    principle\/} is a very important restriction.
  Neither Darwin nor any Darwinian has so far given an
  actual causal explanation of the adaptive evolution
  of any single organism or any single organ.  All that
  has been shown---and this is very much---is that such
  explanations might exist (that is to say, that they
  are logically possible).

\citeasnoun[p.~267]{Popper:TreeOfKnowledge}

\end{quote}

\newpage
\bibliography{v01n04}
\bibliographystyle{tcr}

\newpage
\section*{Acknowledgements\label{acknowledge}}

I am indebted to the School of Electronic Engineering
in DCU (particularly through the agency of its Head,
Charles \mbox{McCorkell}) for continuing encouragement.
All errors remain, of course, my own responsibility.

The article was completed while I was a visiting
researcher (1996/97) with the \hlnk{Swarm Project
  Group}{http://www.santafe.edu/projects/swarm} at the
\hlnk{Santa Fe Institute}{http://www.santafe.edu}.
This visit was made possible by generous support from
\hlnk{Dublin City University}{http://www.dcu.ie} and
the Swarm Project.  Swarm has been supported by Grant
No.~N00014-94-1-G014 from the Department of the Navy,
Naval Research Laboratory, acting in cooperation with
the Advanced Research Projects Agency. Swarm has also
benefited from earlier support from The Carol O'Donnell
Foundation and from Mr.~and Mrs.~Michael Grantham.

%The html version of the article could not have been
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%  HTML}\footnote{\hoturl
%  {http://cbl.leeds.ac.uk/nikos/tex2html/doc/latex2html/latex2html.html}}
%translator developed by Nikos Drakos\footnote{\hoturl
%  {http://cbl.leeds.ac.uk/nikos/personal.html}} and the
%Harvard\footnote{\hoturl
%  {http://www.arch.su.edu.au/\~{}peterw/latex/harvard/}}
%extensions for author/date citations developed by Peter
%Williams\footnote{\hoturl
%  {http://www.arch.su.edu.au/\~{}peterw/index.html}}
%and Thorsten Schnier.

This article is dedicated to the memory of Dr.~John
Kelly, of University College Dublin, who died suddenly
in April 1995. He was my former PhD supervisor, but
more importantly a sincere friend. He is sorely missed.

\section*{Revision History\label{revision}}

Presented at the \emph{Annual Conference on
the Philosophy of Sir Karl Popper}\footnote{\hoturl
{http://www.eeng.dcu.ie/\~{}tkpw/popconf/popconf.html}},
London School of Economics, March 9th, 1996.  The
article title is a somewhat strained allusion to
\cite{Dijkstra:GotoHarmful}---see the relevant entry in
\emph{The Jargon File}\footnote{\hoturl
{http://beast.cc.emory.edu/Jargon30/JARGON\_C/CONSHARM.HTML}}
for more information. This article is derived in part
from material first presented in a much more extensive
technical report \cite{McMullin:Organismic}.

\newpage
\section*{Author Contact Information\label{authors}}

\label{mcmullin}
\hlnk{\textbf{Barry
    McMullin}}{http://www.eeng.dcu.ie/\~{}mcmullin}

\medskip
\noindent\begin{tabular}{ll}
    \multicolumn{2}{l}{\hlnk{Santa Fe Institute}
        {http://www.santafe.edu}}\\
    \multicolumn{2}{l}{\textit{(Visiting Researcher 1996/97)}}\\
    \multicolumn{2}{l}{1399 Hyde Park Road}\\
    \multicolumn{2}{l}{Santa Fe, NM 87501}\\
    \multicolumn{2}{l}{USA}\\[3mm]
    \textbf{Voice:} & \texttt{+1-505-984-8800}\\
    \textbf{Fax:}       & \texttt{+1-505-982-0565}\\
    \textbf{E-mail:}    & \mailto{McMullin@santafe.edu}
\end{tabular}

\bigskip
\noindent\begin{tabular}{ll}
    \multicolumn{2}{l}{\hlnk{School Of Electronic Engineering}
{http://www.eeng.dcu.ie}}\\
    \multicolumn{2}{l}{\hlnk{Dublin City University,}
{http://www.dcu.ie}}\\
    \multicolumn{2}{l}{Dublin 9,}\\
    \multicolumn{2}{l}{IRELAND}\\[3mm]
    \textbf{Voice:}     & \texttt{+353-1-704-5432}\\
    \textbf{Fax:}       & \texttt{+353-1-704-5508}\\
    \textbf{E-mail:}    & \mailto{McMullin@eeng.dcu.ie}\\
    \textbf{Web:}       & \hoturl{http://www.eeng.dcu.ie/\~{}mcmullin}
\end{tabular}
 
\section*{Copyright\label{copyright}}

This article is copyright \copyright~1996 by
\htmlref{Barry McMullin}{mcmullin}.

Permission is hereby granted to private individuals to access,
copy and distribute this work, for purposes of private study
only, provided that the distribution is complete and unmodified,
is accompanied by this copyright notice, and that no charges are
levied; multiple copying for class use in educational
organisations is specifically \emph{permitted}.

The work may \emph{not\/} be accessed or copied, in whole or in part, for
commercial purposes, except with the prior written permission of the
author.

All other rights reserved.

\newpage
\section*{Retrieval\label{retrieval}}

The resources comprising this article are electronically
retrievable, in various formats, via the \hlnk{World Wide Web}
{http://www.w3.org/hypertext/WWW/TheProject}. The base
(directory) URL is:

\begin{quote}
\hoturl{http://www.eeng.dcu.ie/\~{}tkpw/tcr/volume-01/number-04}
\end{quote}

This URL directly accesses the root node of the HTML format
article.  Alternatively, an additional filename may be appended
to this URL, to retrieve one of the other formats, or related
resources, as follows:

\begin{itemize}
\item The complete set of files making up the HTML format of the
article is available in the single compressed archive file
\hoturl{v01n04.html.tar.gz} (53~KByte),
which can be conveniently downloaded for local and/or offline
browsing.
\item  A printable version of the article is available in 
postscript format
as file \hoturl{v01n04.ps} (c.~309~KByte,
42~pages), or in compressed form as 
file \hoturl{v01n04.ps.gz} (c.~105~KByte).
\item The original \LaTeX{} source of the article is available as file
\hoturl{v01n04.tex} (c.~91~KByte), or in compressed form as 
file \hoturl{v01n04.tex.gz} (c.~32~KByte).
\item The \BibTeX{} source for the reference
list is available as file \hoturl{v01n04.bib} 
(c.~16~KByte).
\item Finally, a complete set of all the files just listed
is available as a single compressed 
archive file \hoturl{v01n04.tar.gz}
(c.~228~KByte). 
\end{itemize}

\input{tcrback}

\end{document}
