Acta Biotheor (2010) 58:65–79
DOI 10.1007/s10441-009-9094-9
REGULAR ARTICLE
Multiple Explanations in Darwinian Evolutionary
Theory
Walter J. Bock
Received: 1 November 2009 / Accepted: 1 November 2009 / Published online: 21 November 2009
Springer Science+Business Media B.V. 2009
Abstract Variational evolutionary theory as advocated by Darwin is not a single
theory, but a bundle of related but independent theories, namely: (a) variational
evolution; (b) gradualism rather than large leaps; (c) processes of phyletic evolution
and of speciation; (d) causes for the formation of varying individuals in populations
and for the action of selective agents; and (e) all organisms evolved from a common
ancestor. The first four are nomological-deductive explanations and the fifth is
historical-narrative. Therefore evolutionary theory must be divided into nomological and historical theories which are both testable against objective empirical
observations. To be scientific, historical evolutionary theories must be based on well
corroborated nomological theories, both evolutionary and functional. Nomological
and general historical evolutionary theories are well tested and must be considered
as strongly corroborated scientific theories. Opponents of evolutionary theory are
concerned only with historical evolutionary theories, having little interest in
nomological theory. Yet given a well corroborated nomological evolutionary theory, historical evolutionary theories follow automatically. If understood correctly,
both forms of evolutionary theories stand on their own as corroborated scientific
theories and should not be labeled as facts.
Keywords
Evolution Explanations Nomological theory Historical theory
This paper is based on a lecture presented on 21 September 2009 in a series of seminars organized by the
Columbia University’s Departments of Biological Sciences and of Ecology, Evolution and
Environmental Biology in celebration of the 200th anniversary of Charles Darwin’s birth and the 150th
anniversary of the publication of On the origin of Species.
W. J. Bock (&)
Department of Biological Sciences, Columbia University, 1212 Amsterdam Ave Mail Box 2428,
New York, NY 10027, USA
e-mail: [email protected]
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1 Introduction
In 2009, the 200th anniversary of the birth of Charles Darwin and the 150th
anniversary of the publication of his On the Origin of Species, considerable
divergence still exists on whether a single theory or a bundle of evolution theories
exist and on the exact nature of these diverse theories. In this paper, I would like to
inquire into these questions and to show that a bundle of interrelated evolutionary
theories exists, that these theories are of quite different explanatory types, and the
mode of their testing differs greatly.
The following statements serve as a focus for the themes of this presentation,
namely: (a) ‘‘evolution is a metaphysical research program, but not [nomologically]
scientific.’’—Karl Popper (1957, 1974:133–143; see also Hull 1999); and (b)
‘‘evolutionary biology is a historical science’’—Ernst Mayr (2004:24). Popper later
recanted, but it may have been in the spirit of Galileo in the early 1600s.
Major topics to consider are: (a) evolutionary theory (‘‘mechanisms’’) is
nomological-deductive and scientific; (b) evolutionary theory is also historicalnarrative (not just historical) and scientific; (c) it is necessary to distinguish
nomological evolutionary and historical evolutionary theories; (d) historical
evolutionary theory must be based on nomological evolutionary theory; and (e)
evolutionary theories, either nomological or historical, are neither facts or true, but
rather strongly corroborated scientific theories.
2 Types of Evolution
The verb ‘‘to evolve’’ and the noun ‘‘evolution’’ have the meaning of gradual change
and are so used in several sciences as well as in general use. Darwin (1859)
generally used a tern such as ‘‘change’’, ‘‘modify’’ or ‘‘modification’’ in discussing
transformation from one form to another; he used transmutation only once (see
Barrett et al. 1981). Curiously, his only use of ‘‘to evolve’’ is as the final word in his
book, namely in the sentence: ‘‘There is grandeur in this view of life, with its several
powers, having been originally breathed into a few forms or into one; and that,
whilst this planet has gone cycling on according to fixed law of gravity, from so
simple a beginning endless forms most beautiful and most wonderful have been and
are being evolved.’’ (Darwin 1859:420). For Darwin and most other biologists of his
time, this change of organisms was discussed under the ‘‘transmutation theory.’’ The
term ‘‘evolution’’ was first used in biology for the unfolding of attributes of an
organism during embryological development and subsequently used for changes in
organisms over time (Bowler 1975; see also Richards 1992 who differed with some
of Bowler’s conclusions). The first use of evolution to cover Darwin’s ideas of
transmutation of organisms (Bowler 1975: 106) appears to be by Spencer (1852) in
his essay on ‘‘The development hypothesis’’ in which he writes: ‘‘Those who
cavalierly reject the Theory of Evolution as not being supported by facts…’’
Spencer also used evolution for the embryological development of organisms.
Bowler concluded (pp. 100, 106) that it is probable that Spencer derived the two
applications of evolution from his reading of W. B. Carpenter’s 1851 volume
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‘‘Principles of Physiology, general and comparative. 3rd edition. Spencer earliest
use during the 1850s of ‘‘Theory of Evolution’’ was with reference to embryological
development (Bowler 1975:107) and only denoted evolution in its current meaning
as the history of life in the early 1860s in his First Principles of a New Philosophy
(1860–1862) and in his Principles of Biology (Spencer 1864). Hence the use of
evolution for Darwin’s history of life predated by a couple of years Haeckel’s
(1866) coining of phylogeny for the same concept. General use of evolution for
Darwin’s transmutation began in the last years of the 1860s and the first years of the
1870s; Darwin’s evolutionary history of life and Haeckel’s phylogeny denote the
same historical evolutionary theory (see Mayr and Bock 2002:175) although many
workers still believe that these two terms describe different ordering systems for
living organisms.
The term evolution continued to be used for change of organisms during
ontogenetic development and for transmutation with the latter gradually becoming
dominate and the ontogenetic meaning disappearing well before the end of the
nineteenth century. And little attention was paid to the change of the original
meaning of the Latin evolutio being a rolling out or unfolding of preexisting parts to
change over time. An unfolding of the existing parts of the embryo was the early
concept of evolution in embryology in which the developing organism was an
expansion of preformed or concentrated parts in the fertilized egg. Subsequently
embryological development and transmutation were regarded as some form of
‘‘progressive’’ change with the rejection of the idea of preformation in ontogeny and
increased belief in advances in evolutionary change. Moreover, most biologists and
philosophers from the time of Darwin until the present have considered both forms
of biological evolution, embryological and transmutational, as variants of the same
fundamental process. But this is not so as ontogenetic and evolutionary changes in
organisms are basically different from one another.
Only in the ninth decade of the twentieth century was the important distinction
shown between the two types of processes covered by the term evolution. In an
unfortunately little known, but important, paper, Lewontin (1983) distinguished
between transformational and variational (= populational) evolution (see also, Mayr
1988:15–16; 1997:176). Transformational evolution is change observed in the
attributes of the same object over time, such as the evolution of the earth or the
ontogenetic development of an individual organism.
Variational (or populational) evolution is change observed in the attributes
present in organisms of successive generations; the usual meaning of the term
biological evolution, whether Darwinian or not. Variational evolution is what
Darwin meant when he proposed his idea of transmutational change (sometime also
called populational evolution; see Mayr 1991:43–44, 2001:76–77). Observed
changes in variational evolution are between different objects (individual organisms
of different generations) and are based on populational thinking. Variational
evolution can be defined simply as change observed between organisms over time
(= of different generations) with the minimum time period being one generation
(Bock 2007:92). Variational evolution includes change in attributes existing in
parental and in future offspring generations, i.e., between ancestors and descendants, with a minimum time period of one generation. Any other minimum time
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would be artificial although longer periods are generally considered in discussions
of variational evolution. Variational evolutionary change depends on information
(genetic, learning, etc.) being transmitted from one individual organism to another,
usually from one generation to the next (Bock 2007:95). Variational evolution does
not have to be genetic or heritable as many evolutionary changes are not inherited
genetically and evolution should not be so defined as it is almost always done.
Because of the state of knowledge about inheritance in the 1859s, Darwin was quite
rightly concerned about heritable variation and change in when presenting his ideas
about biological evolution, but sequential work showed that variational evolution
can have nonheritable modes of information transfer from individual to individual.
Transformational and variational evolution observed in living organisms are
completely distinct types of changes and cannot be considered as subcategories of
the same general process of modification over time. Changes in the attributes of the
same individual organism over time (= ontogenetic development) are transformational and are different from variational evolution. ‘‘Ontogeny recapitulates
phylogeny’’ makes no sense; the first is transformational evolution and the second
is variational. They cannot be compared in any meaningful way.
The insistence on including genetics or heredity in definitions of variational
evolution stems from the strong belief that such modifications have to be permanent;
this was the core topic of the manuscript Wallace sent to Darwin in 1958 (Bock
2009b). But permanent change is an artificial and unnecessary restriction for the
definition of variational evolution, both for phenotypic and genotypic change,
although strongly implied by evolutionists whose core work is in genetics (e.g.,
Dobzhansky 1959). In Darwin’s time when ideas on the ‘‘transmutational theory’’
were in their infancy, the ideas that individual phenotypic variation had to be, at
least in part, inherited to result in natural selection, considering natural selection as a
result rather than a cause (Bock 1993: 13–14). For the early Darwinists, the idea that
variational evolution has to be permanent was reasonable because this concept was
new and still little understood. During the past 150 years, a reasonably firm
understanding about causes of variation, both genetical and phenotypical, was
acquired so that variational evolution does not have to be restricted to heritable
changes and does not need be permanent. If differences in attributes of individual
organisms in a population and its descendent population exist, then evolutionary
change has taken place regardless of the basis for the observed difference. Observed
variational [phyletic] evolution can change back and forth from generation to
generation depending on the mode of information transfer between individuals of
successive generations. Moreover, speciation does not have to be permanent as the
intrinsic isolating mechanism (e.g., ecological differences) presently maintaining
two species can break down in the future.
Information associated with evolutionary change is transmitted from organism to
organism (usually between different generations) via several routes (Bock 2007:
95). Clearly the most important is by genetic means, either by the transmission of
DNA or RNA. However, there are several methods of epigenetic transmission.
These include cultural informational transfer which is usually by younger
individuals learning from other individuals, generally but not always, from
members of the same species. Cultural exchange of information is not limited to
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humans but is possible and possibly common in all organisms possessing the ability
to learn such as many species of birds and mammals. Acquiring the species specific
song in young males of song birds (the Oscines; Passeriformes) is almost always by
learning from conspecific adult, or a substitute source. Epigenetic information can
also be passed from generation to generation by chemical particles present in the
cytoplasm of gametes (see Jablonka and Raz, 2009). This means of passing
information from generation to generation may be rather common, but its role in
evolutionary change is insufficiently understood at present. Lastly is what can be
termed template information (Jennings 1937) in which the phenotypical attributes of
the parental generation are used as the basis (= template) for the ontogenetic
development of characteristics of attributes present in the previous generation; this
method is apparently quite rare.
3 Darwinian Evolution
Darwinian evolution is any variational evolutionary change in which selective
agents are one of the nomological causes. And conversely, non-Darwinian
evolution is any variational evolutionary change in which selective agents are not
one of the nomological causes. These non-Darwinian causes could be differential
rates of reproduction of individuals in the population or genetic drift resulting
from chance-based events in determining the breeding population for the next
generation, especially when the actual parental (= breeding) population is a small
segment of the original population. Although many workers have discussed nonDarwinian evolution resulting from genetic drift, its importance in the evolutionary origin of phenotypic features and their further specialization is still under
considerable debate. Basically, it is doubtful that non-Darwinian evolution has
much importance for the evolution of phenotypic features because opposing
selective agents will rather rapidly overwhelm changes brought about by genetic
drift (Hahn 2008) or by differential reproduction rates. Considerable doubt has
been raised on the validity of one of the classic examples of genetic drift—the
evolution of flower color of two forms of Linanthus parryae (Schemske and
Bierzychudek 2001, 2007); this evolutionary change can be well explained by the
action of selective agents.
Two questions about Darwinian evolutionary theory are: (a) Is genetics the core
of evolutionary theory?; and (b) Are all causes for evolutionary change internal to
the organism? The answers to both are strong nos. Genetics was considered by many
workers as the core of evolutionary theory in the belief that heredity is the only
method for transmitting information needed for variational evolution from
individual to individual; this is not the case. Further it is necessary to include
always the essential role of the external environment at several levels in the
interactions between the organism and the external environment (Bock 2002:65,
2003:280). These include the external environment acting as a mutating agent on the
genotype, as a paragenetic agent on the formation of the phenotype during
ontogenetic development and further modifications of the phenotype after development is completed, and as a selective agent on the phenotype.
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4 Evolutionary Processes
Biological evolution consists of two different processes; phyletic evolution which
does not require speciation, and speciation which requires phyletic evolution in at
least one lineage (see Mayr 1959 for good historical analysis of these two
processes). Phyletic evolutionary change (anagenesis) results in modifications in a
species (or clone in asexually reproducing organisms), not in the origin of new
species. It requires the dual evolutionary causes for (1) the formation of new
individual phenotypical variation in the population, and (2) the action of selective
agents arising from the external environment. Genetic drift (see above) will be
excluded for the remainder of this analysis which will consider only the evolution
of phenotypic attributes for which genetic drift apparently plays a very rare role.
Speciation (cladogenesis) results in the evolution of two or more species from a
single ancestral one and requires phyletic evolution in at least one of the separate
lineages plus the additional boundary condition of an external barrier separating
portions of the ancestral species for a sufficient time period to permit the
evolution of intrinsic isolating mechanisms in the separated segments of the
original species. No additional special causes exist for speciation—only those
acting in phyletic evolution, but a distinct boundary condition must exist in the
form of an external barrier which separates two parts of the original species
during the initial period of the speciation process in which they could still
exchange genetic information.
The process of phyletic evolution (anagenesis) is a two-step one, involving (a)
the formation of individual phenotypic variation in the population which is
accidental with respect to current and future selective agents acting on that
population, and (b) the action of selective agents arising from the external
environment on the phenotypic individual organisms which are non-accidental with
respect to the current and future selective agents. The second set of causes have
been designated as ‘‘design’’ in contrast to ‘‘accidental’’ (Mayr 1962) but the term
design is inappropriate for evolutionary analyses (Bock 2009a). One of the goals
before Darwin when he published his theory of transmutation (= evolution) was to
provide a scientific explanation for the apparent design in biology as advocated by
Paley (1802, and most workers previous to 1859); he did this successfully by
showing that these design features of organisms are the result of evolution through
the action of selective agents. Rather than using the terms ‘‘design’’ we should use
the term for this cause and process advocated by Darwin, namely ‘‘adaptation by
natural selection.’’ Although there is no difficulties with the term ‘‘accident’’, I
would propose using ‘‘paradaptation’’ (= besides adaptation; see Bock 1967, 2009a)
in contrast to adaptation for these two evolutionary causes of phyletic evolution, as
these are equivalent to the notions of accidental versus design.
If a process (e.g., anagenesis) involves accidental causes (only one is needed),
then that process and the resulting outcome are also accidental; in this case
accidental with respect to current and future selective agents. Hence since all
characteristics of organisms are the result of phyletic evolution, they are accidental
with respect to the current and future environmental demands and the selective
agents acting on them.
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5 Natural Selection
The term natural selection was used by Darwin (1858, 1859) both as a cause and as
an outcome (Bock 1993, 2009b). His clearest definition was that of an outcome
(Darwin 1859:61) although his major use (1858, 1859) was as a cause. Wallace
(1858) did not use the term natural selection.
The generally accepted modern definition of natural selection is an outcome
(stemming from Fisher 1930) and is: ‘‘nonrandom (differential) reproduction of
genotypes’’ (e.g., Ehrlich and Holm 1963:326); or ‘‘nonrandom differential survival
or reproduction of classes of phenotypically different entities.’’ (Futuyma 1986:555).
Natural selection is used by most biologists (e.g., Lerner 1959; Dobzhansky
1959) quite interchangeably as a cause, a process and an outcome resulting in
massive confusion. Nomological causes act only on individuals, although nomological processes and outcomes (= results) can apply to individuals or groups.
The dual use of natural selection used has led to the development of a hierarchal
theory of evolution with ill-defined notions such as group selection and species
selection which cannot act as nomological causes because groups of individual
organisms and species are not individuals (Bock 2000). These ideas are at best
defined as outcomes and are even doubtful as nomological outcomes; they are
certainly not nomological causes. At best group selection and species selection
might represent generalized observations and it is questionable whether they have
any real value in evolutionary theory.
Natural selection should be restricted to its outcome definition, and should not
used as a cause; if used in both senses, major confusion results as is the present
situation in evolutionary theory. For the cause, the best term is ‘‘selective agent’’
(Bock 1993:15, 2009b: 5) which arises from the interaction between the organism
and the external environment (Bock 1980:218), acts on the phenotype of individual
organisms and is clearly nomological. Selective agents act to eliminate the unsuited
(unfit or least fit) individuals; they do not favor the fittest individuals, only the fit.
‘‘Natural selection is not survival of the fittest’’ (Mayr 2001:118) contrary to
Spencer’s slogan which was accepted by Darwin, and is still widely accepted today
by biologists and the lay public alike. Natural selection is better treated as either
survival of the fit, or as elimination of the unfit.
6 Explanations in Science
A central topic in the philosophy of science is the nature of scientific explanations
(see Simpson 1959: 320 footnote for an early system of explanations in biology;
1963). The typical explanation covered by almost all philosophers is nomologicaldeductive because most of these workers have been interested in physics and other
non-historical sciences. Historical-narrative explanations are almost always avoided
by philosophers of science because they, quite correctly, wish to use law-like
statements in their explanations and do not accept ‘‘historical laws’’ in the erroneous
belief that historical explanations require historical laws. Yet historical-narrative
explanations are most important in any science having a partial historical aspect,
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such as biology and geology. In biology this includes the full explanation of
attributes of organisms which require a historical evolutionary basis. Associated is
the question of full verus partial explanations in biology and has been expressed by
Dobzhansky (1973) as ‘‘Nothing makes sense in biology except in the light of
evolution.’’ This saying, much beloved by evolutionary biologists, is a serious
overstatement as numerous non-evolutionary explanations in biology make great
sense, are most important, and are all that can be achieved and/or desired in most
cases. Most biologists, both scientific and practical (doctors, horticulturists, etc.),
deal mainly or entirely with partial explanations which generally make great sense.
In 2001, after I experienced a strong spasm in my back, started to breathe deeply
and perspire, and subsequently had a CAT scan, I was told that I suffered an aortic
dissection in my descending aorta resulting in an aneurysm. This explanation made
great sense to me although it was only partial without any reference to evolution.
The aneurysm was subsequently repaired.
For any phenotypic attribute, a full explanation includes resolving: (a) Their
existing physical–chemical properties (form, function, biological role, etc.; nomological); (b) Their ontogenetic developments resulting from interactions between the
genotype and the environment (nomological); (c) Their interactions with the
physical external environment (including the adaptiveness of features and the fitness
of individuals; nomological); and, (d) Their historical evolution which is the most
difficult part of full explanations (historical). Full biological explanations are major
tasks in biology with the analysis of the historical evolution of the attributes being
the most difficult part.
Nomological-deductive explanations involve a set of law-like statements,
basically nomological causes, and a set of initial and boundary conditions (Hempel
1965) from which deductions about the particular phenomenon are reached and then
checked against objective empirical observations. Mayr (1961) showed that all
characteristics of living organisms are dependent on a dual set of causes; namely:
(a) functional (or proximal—Mayr’s term) causes are typical nomological-deductive
causes and are sufficient for partial explanations; and (b) evolutionary (or
ultimate—Mayr’s term) causes which are dependent on information passed from
one individual to another and, together with the functional causes, are required for
full explanations in biology.
Nomological-deductive explanations deal with general explanations for a class of
phenomena (or objects) asking how has each observed phenomenon has occurred.
They answer the question how has a particular phenomenon occurred, apply to
universals (all members of a particular class independently of space and time), do
not depend on the past history of the phenomena being explained, and their premises
(the nomological statements) are assumed to be always true. The deduction is then
compared with objective empirical observations of the phenomenon. If the
observations agree with the deduction, the explanation is accepted. If the deduction
disagrees with the observations, the N-D E has been falsified and the reasons for the
falsification must be ascertained; the failure need not be because the nomological
causal statement is wrong; the initial and boundary conditions could be incorrect, or
the objective empirical observations could be at fault.
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Contrary to the beliefs of most philosophers, not all science is nomological; a
diversity of explanations may exist with historical-narrative explanations being
important in some sciences, e. g. biology and geology, which are partly to largely
historical so that an important portion of their explanations are historical-narrative.
The two modes of explanations, nomological and historical, differ in the many ways
of how they are expressed, tested, and used to test other theoretical statements.
Historical explanations provide an understanding of the existing attributes of a
particular set of phenomena (a singular) at a specified place and a definite point in
time; these explanations absolutely depend on the past history of these phenomena
and are scientific only if they are based on pertinent nomological-deductive
explanations.
Explanations of historical events must be based on pertinent, well corroborated
nomological-deductive explanations to be scientific. Historical-narrative explanations are stated on a non-deductive, probabilistic basis with the hope of reaching the
most reasonable explanation for the phenomena studied. Tests of historical-narrative
explanations use objective, empirical observations, but are largely inductive, not
deductive, as these explanations are for singular phenomena or events. Science is
not just deductive as claimed by a number of philosophers, but many explanations in
some sciences are inductive. Mr. Sherlock Holmes solved his famous cases by
induction rather than by deduction as he claimed often to Mr. James Watson.
Historical-narrative explanations are historical in character, which means that
earlier events provide the initial conditions for explaining later events. Great care
must be given to formulating the analysis with the presumed correct chronological
order of events and changes, such as the sequence of events in the evolution of avian
flight or of the mammalian jaw articulation.
Aspects of historical-narrative explanations are: (a) to be scientific, they must be
based on pertinent, well tested N-D Es; (b) they must be tested against objective,
empirical observations including the underlying N-D Es and the objective, empirical
observations used to test them; (c) acceptance of a particular H–N E is always given
on a probability basis because these explanations often employ a number of often
conflicting N-D Es and because of the usual considerable uncertainty over the initial
and boundary conditions involved in the explanation; (d) they are not universal in
that a successful H–N E for one phenomenon (avian homoiothermy) need not hold
for a similar phenomenon (mammalian homoiothermy) even if some of the N-D Es
included in both H–N Es are the same; (e) because of their complexity, the possible
confusion between competing explanations and the difficulty in identifying valid
confirming or falsifying tests, H–N Es must be stated clearly and in the proper
chronological order to insure meaningful tests or appraisal of rival H–N Es; (f)
generally the more precisely a H–N E is stated, the more difficult it is to test and
support. That humans had evolved from a chimpanzee-like ancestor is much more
difficult to support than humans had evolved from an anthropoid ancestor which is
more difficult to support than humans had evolved from a primate ancestor, and etc.;
and, (g) a H–N E is for single events and hence a H–N E cannot be used to test any
N-D Es or any other H–N Es, be they general or special.
Historical-narrative explanations in biology include the historical evolution (=
phylogeny) and classification of organisms and the evolutionary history of their
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attributes—that is, anything related to the history of life, such as classification,
phylogeny and historical biogeography. The ‘‘tree of life’’ is a historical
explanation. All full explanations in biology include H–N Es which is why they
are so difficult to formulate and test. Because they deal with singular events,
particular historical scientific theories cannot be used to test any other scientific
theories, be they nomological or historical. Both N-D Es and H–N Es are scientific
under the criterion of demarcation for scientific explanations advocated by most
philosophers of science in that they are both available for testing against objective,
empirical observations.
The accuracy of many valid tests of H–N Es may be weak (non-robust), and a
distinction must be made between valid tests and robust tests. Simply because an
empirical test does not always provide the correct answer (= non-robust), as can be
common in historical explanations, does not mean that it is an invalid test.
7 Evolutionary Theories
Darwin always spoke about my theory—in the singular. But he actually presented
five distinct theories as pointed out by Mayr (1985) although Darwinian
evolutionary theory is generally still discussed today as a single theory. The first
four evolutionary theories are well corroborated nomological-deductive explanations (but not facts) having been tested with many, many objective empirical
observations. These four theories are: (a) evolution, as such, is the theory that states
that all populations of organisms change over time, with the minimum time period
being one generation; (b) evolutionary change is gradualistic in that it takes place in
steps of the magnitude seen between parents and offspring and never in large sudden
saltations or jumps; (c) evolutionary change includes at least two processes, namely
phyletic transformation (anagenesis) and speciation (cladogenesis) although Darwin
(1859) did not discuss the latter in any detail. Multiplication of species comprises
splitting of phylogenetic lineages as well as phyletic change within, at least, one of
the lineages; and (d) evolutionary change takes place as the result of a small number
of causes, of which the most important are the origin of phenotypically varying
individuals in the population and sorting of these varying individuals by selective
agents arising from the external environment.
The fifth evolutionary theory of Mayr is a well corroborated historical-narrative
explanation (but not a fact); namely: (e) evolutionary change is common descent
which implies that all species or populations of organisms have descended with
modification from common ancestors; this descent includes both phyletic modification and phyletic branching.
Darwinian common descent is equivalent to Ernst Haeckel’s phylogeny (1866) as
the term evolution was not commonly used in this sense until the early 1870s,
although Spencer (1864) used evolution in the sense of Darwin’s fifth theory
slightly prior to Haeckel’s original proposal of phylogeny (see Bowler 1975).
Because of the differing nature between the first four of these theories and the
fifth, evolutionary theory should be subdivided into nomological evolutionary
theory and historical evolutionary theory with the latter depending completely on
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the former to be scientific. Darwin clearly realized that he had to provide a
convincing set of nomological causes supporting his concept of historical evolution
of organisms which he did successfully with his proposal of natural selection.
Almost everyone accepting the idea of variational evolution after 1859 were only
interested in historical evolution with the central core of Darwinian nomological
evolutionary theory—natural selection—being ever increasingly disregarded during
the remaining decades of the18th century and considered dead by the early1900s by
many workers such as Rádl and Nordenskiöld (Bowler 1989: 246). Nordenskiöld
(1928: 616) in a confusing penultimate paragraph in his book wrote: ‘‘First of all,
selection: that it does not operate in the form imagined by Darwin must certainly be
taken as proven, but does it exist at all?’’ The widespread failure of many, or most
evolutionary biologists, to understand Darwinian natural selection was due to their
lack of understanding the critical role of organism-environment interactions, a
problem that continues to the present.
Nomological evolutionary theories are primary and historical evolutionary theory
secondary; they must be considered and discussed in that order. It is incorrect to
speak first of the pattern of evolutionary change (= historical theory) and, based on
this pattern, the process of evolutionary change (= nomological theory). Classification and phylogeny are historical and must be based on nomological evolutionary
theory. The fifth of Darwin’s theories—that of common descent—is a general
historical theory and has been tested successfully against a large number of
objective empirical observations, namely: (a) groups of related organisms are found
non-stochastically over the surface of the earth depending on their degree of
evolutionary relationship and their abilities to disperse over barriers; (b) the first
occurrence of groups of organisms is found earliest chronologically in the fossil
record depending on their ancestral-descendent relationships and the goodness of
the fossil record; and, (c) vestigial structures are found in descendent groups with
the same structure being well developed and functional in ancestral groups.
In addition to the general historical theory of evolution, endless special theories
exist which deal with the evolutionary history and classification of all groups of
organisms at all hierarchal levels from subspecies to kingdoms. Special historical
evolutionary theories include such questions as whether: (a) are rodents and rabbits
closely related to one another within the true mammals forming the taxon Glires?;
(b) do the Pinnipedia (seals and other aquatic carnivores) have a single or a double
origin from the terrestrial carnivores?; and, (c) did birds descend from some early
group within the archosaurian reptiles or from a later and more specialized group
within the theropod dinosaurs? The evolutionary history of individual traits, such as
flight in bats, or obligatory homeothermy in birds, are also special historical
evolutionary theories. Special historical evolutionary theories deal with singular
events and each must be tested independently against objective, empirical
observations, which generally include an argument chain of well tested nomological
theories and the empirical observations supporting them. To be scientific, historical
evolutionary theories, both the general and the numerous special, must also be tested
against relevant, well corroborated nomological evolutionary theory. Even if the
general historical evolutionary theory is well tested and corroborated, it cannot be
used to test any special historical evolutionary theory. Any historical evolutionary
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W. J. Bock
theory must also be tested using other well corroborated non-evolutionary
nomological theories, such as nomological theories about functional properties of
muscle-bone systems, ecological relationships, etc.
A historical evolutionary theory on the origin of avian flight must also be tested
against nomological aerodynamic theories as well as those concerning functional
properties of vertebrate muscle-bone systems, metabolism, respiration, and etc. If a
well tested and convincing historical theory has been reached to explain the
evolution of avian flight, that historical theory serves for birds only and cannot be
applied to explain the evolution of flight in bats or in pterosaurs, each of which is a
different singular event. Being historical in nature, all such explanations in
evolutionary biology, including classifications and phylogenies, cannot be based on
ideas of deductive explanations in science as advocated by Popper (1959), Hempel
(1965), Nagel (1961) contrary to the claims of many workers (e.g., Platnick and
Gaffney 1978; see Bock 2004).
8 Anti-evolutionary Objections
Objections to evolution are basically restricted to disagreeing with historical
evolutionary theory, with almost no interest in nomological evolutionary theory;
these objections arise almost entirely with whether humans have evolved from some
other organism or were created separately from other organisms. It is not possible to
exclude humans from any general historical evolutionary theory that organisms
evolved from common ancestors; hence all theories about historical evolution, both
general and special, have to be rejected if one accepts the origin of humans as
special creation. Hence, acceptance or rejection of nomological evolutionary theory
does not matter as the significant issue is rejection of historical evolutionary
theories.
Distinguishing between nomological and historical evolutionary theories permits
independent testing of both theories. The testing of nomological evolutionary theory
has been most extensive so that this theory can be considered as exceedingly well
corroborated in the sense of Popper (1959). The objective empirical observations
serving as these tests include: (a) overwhelming observations of the origin of
genetic and other individual variation in populations; (b) numerous observations of
the action of selective agents both natural and artificial; (c) directly observed cases
of phyletic evolution, both experimental (e.g., animal and plant breeding) and
natural, including the development of resistance by numerous species of insects to
insecticides and of numerous bacteria to antibiotics); and, (d) directly observed
cases of speciation, mostly in animal and plant breeding. It should be noted that the
extreme size breeds of dogs such as chihuahuas and Irish wolfhounds would
represent distinct species in nature, being separated by mechanical intrinsic isolating
mechanisms because of their size differences. In addition botanists have reproduced
many natural allotetraploid species of plants which have evolved naturally by
hybridization followed by doubling of the chromosomes in the hybrid organism as
well as creating new allotetraploid species such as such as Raphanobrassica from
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77
the domestic cabbage and radish (e.g., Ehrlich and Holm 1963:190–191, Grant
1981:248).
9 Conclusions
A number of major conclusions may be reached, namely: (a) Analysis of
evolutionary theories must be those understood today, not that published by
Darwin one hundred and fifty years ago; considerable progress has been made since
1859. (b) A single evolutionary theory as considered by Darwin does not exist, but
several evolutionary theories occur with clear distinctions made between nomological and historical evolutionary theories, the latter being separated into a general
and numerous special theories. (c) Although evolutionary theories still suffer from
poor definition of many terms, such as adaptation and the niche, and/or from
multiple use (pluralism) of the same term for several distinctive concepts, such as
natural selection, both of which result in serious confusion, this does not affect the
overall strong corroboration of both nomological and historical evolutionary theory.
(d) Nomological evolutionary theory and general historical evolutionary theory
have been exceedingly well tested and are strongly corroborated scientific theories.
The testing and corroboration of special historical evolutionary theories varies
greatly from being strong to exceedingly weak, but this range of testing and
corroboration does not affect the strong corroboration of both nomological and
general historical evolutionary theories. (e) Given a well corroborated nomological
evolutionary theory and sufficient time, then historical evolutionary theory follows
automatically just as the historical theory of continental drift follows the
nomological theory of plate tectonics. Acceptance of nomological evolutionary
theory means that historical evolutionary theory must also be accepted; no other
possibility exists. (f) If understood correctly, both nomological and historical
evolution stand on their own as strongly corroborated scientific theories. Neither
have to be further embellished as a fact or as true.
References
Barrett PH, Weinshank DJ, Gottleber TT (1981) A concordance to Darwin’s origin of species, 1st edn.
Cornell University Press, Ithaca, xv ? 834 pp
Bock WJ (1967) The use of adaptive characters in avian classification. In: Snow DW (ed) Proceedings of
the XIV international ornithological congress, pp 61–74. Blackwell, Oxford
Bock WJ (1980) The definition and recognition of biological adaptation. Am Zool 20:217–227
Bock WJ (1993) Selection and fitness; definitions and uses; 1859 and now. Proc Zoolog Soc Calcutta,
Haldane Comm vol, pp 7–26
Bock WJ (2000) Towards a new metaphysics: the need for an enlarged philosophy of science. Biol Philos
15:603–621
Bock WJ (2003) Ecological aspects of the evolutionary processes. Zool Sci 20:279–289
Bock WJ (2004) Explanations in systematics. In: Williams D, Forey PL (eds) Milestones in systematics.
London: systematics association special, vol Ser 67. CRC Press, Boca Raton, pp 49–56
Bock WJ (2007) Explanations in evolutionary theory. J Zoolog Syst Evol Res 45:89–103
123
78
W. J. Bock
Bock WJ (2009a) Design—an inappropriate concept in evolutionary theory. J Zool Syst Evol Res
47(1):7–9
Bock WJ (2009b) The Darwin–Wallace myth of 1858. Proc Zool Soc Calcutta 62(1):1–12
Bowler PJ (1975) The changing meaning of ‘‘Evolution’’. J Hist Ideas 36(1):95–114
Bowler PJ (1989) Evolution. The history of an idea. University of California Press, Berkeley (Revised
Edition, xvi ? 432 pp)
Darwin C (1858) On the tendency of species to form varieties; and on the perpetuation of varieties and
species by natural means of selection. J Proc Linn Soc Zool 3:46–52
Darwin C (1859) On the origin of species. London, John Murray; Facsimile of the first edition. Harvard
University Press, Cambridge, ix ? 513 pp
Dobzhansky T (1959) Variation and evolution. Proc Am Philos Soc 103(2):252–263
Ehrlich PR, Holm RW (1963) The process of evolution. McGraw-Hill, New York, xvi ? 347 pp
Fisher RA (1930) The genetic theory of natural selection. Clarendon Press, Oxford (Revised Edition New
York, Dover)
Futuyma DJ (1986) Evolutionary biology, 2nd edn. Sinauer Associates, Sunderland, xii ? 600 pp
Grant V (1981) Plant speciation, 2nd edn. Colunbia University Press, New York, iii ? 563 pp
Hahn MWE (2008) Toward a selection theory of molecular evolution. Evolution 62(2):255–265
Hempel CG (1965) Aspects of scientific explanations. Free Press, New York
Hull D (1999) The use and abuse of sir Karl Popper. Biol Philos 14:481–504
Jablonka E, Raz G (2009) Transgenerational epigenetic inheritance: prevalence, mechanisms, and
implications for the study of heredity and evolution. Q Rev Biol 82(2):131–176
Jennings HS (1937) Formation, inheritance and variation of the teeth in Difflugia corona. A study of the
morphogenic activities of rhizopod protoplasm. J Exp Zool 77:287–336
Lerner IM (1959) The concept of natural selection: a centennial view. Proc Am Philos Soc 103(2):
173–182
Lewontin R (1983) The organism as the subject and object of evolution. Scientia 118:63–82
Mayr E (1959) Isolation as an evolutionary factor. Proc Am Philos Soc 103(2):221–230
Mayr E (1962) Accident or design: the paradox of evolution. In: The evolution of living organisms.
Proceedings of the Darwin Centenary Symposium of the Royal Society of Victoria, Melbourne,
1959. Melbourne University Press, Melbourne, pp 1–14
Mayr E (1988) Toward a new philosophy of biology. Harvard University Press, Cambridge, x ? 564 pp
Mayr E (1991) One long argument. Charles Darwin and the genesis of modern evolutionary thought.
Harvard University Press, Cambridge, xiv ? 195 pp
Mayr E (1997) This is biology. The science of the living world. Harvard University Press, Cambridge,
xv ? 327 pp
Mayr E (2001) What evolution is. Basic Books, New York, xvii ? 318 pp
Mayr E (2004) What makes biology unique? Considerations on the autonomy of a scientific discipline.
Cambridge University Press, New York, xiv ? 232 pp
Mayr E, Bock WJ (2002) Classifications and other ordering systems. Z Zool Syst Evol Forsch 40:1–25
Nagel E (1961) The structure of science: problems in the logic of scientific explanation. Brace and World,
New York
Nordenskiöld E (1928) The history of biology. A survey. Tudor Publishing, New York, xii ? 616 ?v pp
Paley W (1802) Natural theology; or evidences of the existence and attributes of the diety, collected from
the appearances of nature. R. Faulder, London
Platnick NI, Gaffney ES (1978) Systematics and the Popperian paradigm. Syst Zool 27:381–388, 1978b
Popper K (1957) The poverty of historicism. Routledge & Kegen Paul, London (Boston, Ma., Beacon
Press), xiv ? 166 pp
Popper K (1959) The logic of scientific discovery. Hutchinson & Co., London
Popper K (1974) Autobiography of Karl Popper. In: Schilpp PA (ed) The philosophy of Karl Popper. Part
one. Open Court, LaSalle, pp 2–181 xvi ? 670 pp
Richards RJ (1992) The meaning of evolution. University of Chicago Press, Chicago, xv ? 205 pp
Schemske DW, Bierzychudek P (2001) Perspective: evolution of flower color in the desert annual
Linanthus parryae: wright revisited. Evolution 55(7):1269–1282
Schemske DW, Bierzychudek P (2007) Spatial differentiation for flower color in the desert annual
Linanthus parryae: was wright right? Evolution 61(11):2528–2543
Schilpp PA (ed) (1974) The philosophy of Karl Popper. The library of living philosophers, vol XIV, Two
books. Open Court, La Salle
123
Multiple Explanations in Darwinian Evolutionary Theory
79
Simpson GG (1959) Anatomy and morphology; classification and evolution: 1859 and 1959. Proc Am
Philos Soc 103(2):286–306
Simpson GG (1963) Biology and the nature of science. Science 134(3550):81–88
Spencer H (1852) The development hypothesis. Republished in Spencer, 1896. Essays scientific and
political. vol I:1–7. New York (from Bowler, 1975. p 106)
Spencer H (1864) Principles of biology. London (from Bowler, 1975. p 108)
Wallace AR (1858) On the tendency of species to form varieties; and on the perpetuation of varieties and
species by natural means of selection. J Proc Linn Soc Zool 3:53–632
123