Neo-Darwinism and - IA de Investigación especializada en el MIT

Neo-Darwinism and
Evo-Devo: An Argument
for Theoretical Pluralism
in Evolutionary Biology

Lindsay R. Craig
Temple University

There is an ongoing debate over the relationship between so-called neo-Darwinism
and evolutionary developmental biology (evo-devo) that is motivated in part
by the possibility of a theoretical synthesis of the two (p.ej., Amundson 2005;
Brigandt and Love 2010; Laubichler 2010; Minelli 2010; Pigliucci and
Müller 2010). Through analysis of the terms and arguments employed in this
debate, I argue that an alternative line of argument has been missed. Específicamente,
I use the terms of this debate to argue that a relative signiﬁcance issue (Beatty
1995, 1997) exists and reﬂects a theoretical pluralism that is likely to remain.

Introducción

1.
The relatively new ﬁeld of evolutionary developmental biology (evo-devo)
continues to attract considerable attention from biologists, philosophers,
and historians, en parte, because work in this ﬁeld demonstrates that impor-
tant changes are underway within biology (p.ej., Gilbert, Opitz and Raff
1996; Amar 2003; Amundson 2005; Burian 2005a; Müller and Newman
2005; Laubichler 2007, 2010; Müller 2007; Pigliucci 2007, 2009; Minelli
2010). Though studies of development and evolution were closely connected
during the 19th century, continued work in genetics fostered a general split
between the two during the ﬁrst decades of the twentieth century (p.ej.,
allen 1978; Gilbert 1978; Mayr and Provine 1980; Gilbert, Opitz and Raff
1996). Como consecuencia, embryology and developmental biology did not play a
signiﬁcant role in the development of so-called neo-Darwinism1 during the

Thanks to Richard Burian, Michael Dietrich, and Robert Richardson for comments on earlier
versions of this paper.

1. The term neo-Darwinism is problematic; its contemporary usage is prone to ambiguity
and confusion. Aquí, I use the term and its derivatives in order to remain consistent with
the language of the debate that is my current focus. I attempt to specify the usage of the
term in this debate in section 2.1 abajo.

Perspectives on Science 2015, volumen. 23, No. 3
©2015 by The Massachusetts Institute of Technology

doi:10.1162/POSC_a_00167

243

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244

Neo-Darwinism and Evo-Devo

Modern Synthesis of the mid-twentieth century (p.ej., allen 1978; Mayr and
Provine 1980; Hamburger 1988; Maienschein 1991; Gottlieb 1992; Gilbert
1994; Gilbert, Opitz and Raff 1996). Evo-devo, which emerged as a ﬁeld of
study in the 1980s and continues to grow well into the current millennium,
focuses on the intersection of individual development and evolutionary
change to explain evolutionary phenomena such as the origin of novel mor-
phological structures, the evolution of developmental systems and their
componentes, and morphological diversity within and between taxonomic
grupos. By investigating evolutionary phenomena that are causally related
to developmental processes, evo-devo casts development in a staring role
in the study of evolution.

En efecto, the relationship between neo-Darwinism and evo-devo has fos-
tered much debate in recent years (p.ej., Amundson 2005; Müller 2007;
Pigliucci 2009; Brigandt and Love 2010; Craig 2010; Laubichler 2010;
Minelli 2010). A strong motivation, though not the only motivation, para
discussing the relationship is the possibility of a theoretical synthesis of
neo-Darwinism and evo-devo that results in, or at least does much to pave
the way toward, a synthetic theory of evolution applicable to all evolutionary
phenomena (p.ej., Amundson 2005; Müller 2007; Pigliucci 2009; Brigandt
y amor 2010; Laubichler 2010; Minelli 2010). Whether such a synthesis is
possible depends on the relation between the two frameworks. Eso es, if the
two fundamentally conﬂict or contradict, a theoretical synthesis of them is less
likely, or at least will take more theoretical, conceptual, and empirical work,
than if the two are compatible or complementary. So, to answer whether
a synthesis of neo-Darwinism and evo-devo is possible, many have taken a
necessary step back to address the relationship between the frameworks.

In The Changing Role of the Embryo in Evolutionary Thought (2005), Ron
Amundson provides a comprehensive narrative of the relationship between
development and evolution from pre-Darwinian thought through the start
of the twenty-ﬁrst century. He ends his account with discussion of recent de-
bates related to neo-Darwinism and evo-devo, including the debate regarding
a synthesis of the two. At the start of his ﬁnal section titled “A Newer
Synthesis?,” he insists that “[t]he ﬁeld of evo-devo is changing so fast that
predictions about its future relations with neo-Darwinism are foolhardy”
(pag. 250). Para él, the two currently conﬂict in serious ways, but despite
his skepticism, Amundson very cautiously concludes that with the continued
success of both, they may be shown to be consistent and a synthetic theory
may be possible (2005, pag. 257). Similarmente, Alessandro Minelli (2010) argues
that though a synthesis of neo-Darwinism and evo-devo has proved difﬁcult,
they are complementary nonetheless and a “natural integration” is possible
(pag. 224). Massimo Pigliucci and Gerd Müller (2010) argue that evo-devo
is part of the extension of neo-Darwinism (pag. 12). On the other side of the

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Perspectives on Science

245

debate are those who believe that there are serious insurmountable conﬂicts be-
tween neo-Darwinism and evo-devo. Por ejemplo, Manfred Laubichler (2010)
claims that evo-devo conﬂicts with neo-Darwinism to the extent that evo-devo
represents a Kuhnian paradigm shift within evolutionary biology (pag. 200).

My view is that this debate misses an important line of argument in favor
of theoretical pluralism—the accommodation and pursuit of more than one
explanatory framework—in evolutionary biology. The terms and existing
arguments of this debate stipulate that neo-Darwinism and evo-devo explain
different evolutionary phenomena by way of different explanatory frame-
works that are well supported by the available evidence. In what follows,
I use the terms and arguments set forth by these authors to argue that a rel-
ative signiﬁcance issue (Beatty 1995, 1997), which concerns the extent of
applicability of two different explanatory frameworks, currently exists be-
tween neo-Darwinism and evo-devo. Eso es, Actualmente, both neo-Darwinism
and evo-devo explain or account for some evolutionary phenomena, cual
raises the question of the signiﬁcance of these explanatory frameworks relative
to one another. Like Amundson, I believe that there is an element of foolish-
ness in making too strong claims about the future relations between neo-
Darwinism and evo-devo precisely because continued experimental and
explanatory successes will drive those relations in directions with unforesee-
able details. But a look at the current state of things allows for mediated
claims about what may come to be the case. Rather than argue that a synthe-
sis is or is not possible, claims that may indeed be too strong at this point, I
use the current relative signiﬁcance issue to argue further that to continue to
account for different evolutionary phenomena, more than one explanatory
framework may obtain instead. Theoretical pluralism may prevail in evolu-
tionary biology. That neo-Darwinism and evo-devo, two very conceptually
different explanatory frameworks, explain different kinds of evolutionary
phenomena suggests that a relative signiﬁcance issue currently exists between
the two, and this issue of relative signiﬁcance suggests that both will continue
to develop as relatively independent and distinct frameworks.

To be clear, I am not concerned with resolving the relative signiﬁcance
issue between neo-Darwinism and evo-devo. De hecho, I am not convinced that
it is possible to answer which of these frameworks correctly accounts for the
largest proportion of evolutionary phenomena, the underlying question of all
relative signiﬁcance disputes. At the very least, there are a large number of
experimental, epistemological, and metaphysical tangles to be combed out
before such an answer could be conﬁdently proposed. My concern here is
to contribute to the debate over the relation between and synthesis of
neo-Darwinism and evo-devo. I plan to do this by making clear and expand-
ing upon what has been previously missed by the debate’s participants,
a saber, the relative signiﬁcance issue that suggests that neo-Darwinism

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246

Neo-Darwinism and Evo-Devo

and evo-devo will remain unsynthesized, individual explanatory frameworks.
Además, I take this to be a more moderate claim than those espoused in the
debate up to this point. En particular, the following argument does not ad-
dress whether a synthesis is possible because, as Amundson points out, semejante
a possibility is at least partially dependent upon more immediate develop-
mentos. Instead of staking a claim on the possibility question, I contend that
the current debate has missed something important, the relative signiﬁcance
issue between neo-Darwinism and evo-devo, and this issue is important
to this debate because it presently indicates that the two will continue to
develop as individuals rather than participate in a theoretical synthesis.

To support my view, and to avoid confusion, the following section is de-
voted to clariﬁcation of the two major terms of this debate, neo-Darwinism
(sección 2.1) and evo-devo (sección 2.2), and review of the arguments pro-
vided by Amundson (2005), Minelli (2010), Pigliucci and Müller (2010),
and Laubichler (2010) (sección 2.3). In section three, I use the terms
and arguments of the current debate to illustrate that neo-Darwinism
(sección 3.1) and evo-devo (sección 3.2) explain different evolutionary
phenomena, a considerable aspect of all relative signiﬁcance issues. Secciones
two and three lay the groundwork for my argument in section four that the
relative signiﬁcance controversy between neo-Darwinism and evo-devo indi-
cates that the two will survive as individual frameworks. Finalmente, section ﬁve
includes concluding remarks.

2. Neo-Darwinism and Evo-Devo: The Current Debate
Those engaged in the ongoing debate over the relationship between neo-
Darwinism and evo-devo deﬁne neo-Darwinism and evo-devo in importantly
similar ways. Analysis of this debate and my argument that there is a rel-
ative signiﬁcance issue in the midst require a close look at how these terms
are used by these authors. Once these terms are generally deﬁned within
the context of the debate, the different arguments concerning the relation-
ship between the two offered by Amundson, Minelli, Pigliucci and Müller,
and Laubichler will be examined as well.

2.1 Neo-Darwinism Deﬁned
Amundson, a philosopher and “self-styled” historian of biology (2005, pag. 2),
devotes four out of eleven chapters of his book to the Evolutionary Syn-
thesis2, an episode in twentieth century history of biology during which
pivotal theoretical, conceptual, and experimental strides were made in evo-
lutionary biology. In these chapters, which follow Amundson’s detailed
account of the relationship between development and evolution prior to

2. The Evolutionary Synthesis is also known as the Modern Synthesis.

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Perspectives on Science

247

the Synthesis, he describes the nature of the Synthesis, reactions to it, y
ongoing debates that have sprung from it. The section immediately pre-
ceding his characterization of the Synthesis acknowledges that there are a
number of difﬁculties associated with a deﬁnitive description of this com-
plicated period, and despite numerous attempts to develop such a descrip-
ción, “the Synthesis as a scientiﬁc and historical entity remains elusive”
(pag. 162). Of particular interest to Amundson, and what he describes as
the inspiration for his book, is the somewhat contentious claim that devel-
opmental biology played no role in the Synthesis (pag. 162). Analysis of this
claim requires a description of the Synthesis, and it is from this description
that the reader receives a more detailed understanding of Amundson’s take
on neo-Darwinism.

For Amundson, the Evolutionary Synthesis, which he places between the
1930s and 1940s, led to the “mainstream of evolutionary biology” (pag. 1), o
neo-Darwinism. Curiosamente, on the second page of his introductory chap-
ter, Amundson states that his interest is not in the theoretical and method-
ological debates between scientiﬁc theories but is instead in those debates
between “scientiﬁc views” (pag. 2). Qué, exactly, Amundson takes to be
the differences between scientiﬁc theories, Por un lado, and scientiﬁc
puntos de vista, en el otro, is somewhat unclear, but his account of the Synthesis
and neo-Darwinism sheds some light on the matter. In contrast to a descrip-
tion of neo-Darwinism as a concrete and identiﬁable theory of evolution
that epitomizes a contemporary research program, Amundson characterizes3
neo-Darwinism more generally as a way of thinking about and explaining
evolution, an “approach” (p.ej., pag. 236), “perspective” (p.ej., pag. 237), o
“viewpoint” (p.ej., pag. 237) for understanding the components and processes
of evolutionary change. En efecto, part of what typiﬁes neo-Darwinism on his
account is what he refers to as “population thinking,” or thinking of evolu-
tionary change in terms of organismal populations with particular genetic
makeups that are maintained and reﬁned over time. This way of thinking
about evolution is fostered by population genetics, cual, he argues, es
genuinely inconsistent with developmental or “typological thinking”—
thinking of evolutionary change in terms of developmental processes and
componentes, morphological traits, and how they change over time—
contemporarily demonstrated by evo-devo practitioners (pag. 225). I believe
that Amundson takes neo-Darwinism to be more general than a speciﬁc,
discrete theory of evolution. Para él, contemporary neo-Darwinism is best

3. Amundson also refers to neo-Darwinian theory throughout the book. Given his character-
ization of both neo-Darwinism and evo-devo, sin embargo, I suspect that his use of theory is the result
of convention, of how we speak about certain scientiﬁc entities, and does not indicate a particular
commitment to neo-Darwinism as such. I say more about this in the following pages.

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248

Neo-Darwinism and Evo-Devo

characterized as a pervasive view of evolution with a particular—though
muddy—history, conceptual commitments, and related implications rather
than as an axiomatization, or semantic, hierarchical, or structural model of
the principles, laws, and relations relevant to evolutionary processes, com-
ponents, and outcomes. Amundson’s introductory statement that he is inter-
ested in scientiﬁc views rather than scientiﬁc theories is indicative of what
neo-Darwinism represents in the larger debate; as I argue in the rest of this
sección, each of the authors involved provide descriptions of neo-Darwinism
that are similarly general.

Contemporary neo-Darwinian commitments, according to Amundson,
can be traced back, en parte, to population genetics, which demonstrates
the compatibility of Mendelian inheritance and Darwinian natural selection.
He describes population genetics as part of the “early core” of the Evolution-
ary Synthesis from which neo-Darwinism resulted. Another part of the “early
core” of the Synthesis is the Mendelian-chromosomal theory of heredity
(pag. 163), which claims that chromosomes are the basis for genetic inheri-
tance since chromosomes are sequences of Mendelian “factors” or “particles,"
later referred to as “genes,” at particular loci associated with adult characters
or traits. A third component of this core is the demonstrated consistence of
population genetics with variation in wild populations by way of ﬁeld stud-
es (pag. 163). More generally, Amundson says that the “core of the Synthesis
was the formal description of populations that was enabled by population
genetics” (pag. 163). His discussion of the core of the Synthesis illustrates that
Amundson’s take on “neo-Darwinian thinking”, a phrase he uses through-
afuera, is partially characterized by a population approach, or population think-
En g, to understanding and explaining evolution.

Also at the foundation of neo-Darwinian thinking are the views that
natural selection is the primary mechanism of evolution (pag. 131) y eso
macroevolutionary change is the result of microevolutionary processes.
Amundson points out that other areas of study within biology reexamined
their specialized theories “in ways that were consistent with this core”
(pag. 163). Amundson is somewhat vague about which specializations were
involved in this reinterpretation, though he does argue that “ontogenetic
development of individual organisms had no place in this framework” (pag. 1).
So, developmental insights, on Amundson’s account, did not signiﬁcantly
impact neo-Darwinian thinking. This is largely because neo-Darwinism,
with its population genetics foundation, identiﬁes genes by tracking associ-
ated phenotypes through generations, which allows for explanations of gener-
ational gene sorting (pag. 7) and renders ontogenetic causal processes irrelevant
(pag. 161). The ontogenetic relationship between genes and phenotypes is
black-boxed within neo-Darwinism (pag. 212); eso es, the ontogenetic causal
processes that are the causal bridges between genes and phenotypes are taken

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Perspectives on Science

249

as unimportant to patterns of gene transmission over generational time
according to Amundson’s account.

In his characterization of the Synthesis and neo-Darwinism, Amundson
appeals to Wolf-Ernst Reif, Thomas Junker, and Uwe Hoßfeld’s analysis of
the so-called Synthetic Theory of Evolution (2000). Aquí, también, is evidence
that Amundson’s description of neo-Darwinism is of a mainstream way of
thinking or a predominant approach to understanding evolution rather than
a more concrete scientiﬁc theory. Reif and his colleagues take aim at tradi-
tional analyses of the Evolutionary Synthesis and its result, the Synthetic
Teoría (Reif et al., pag. 42), which they argue is different from neo-Darwinism
(Reif et al., pag. 43). They claim that while neo-Darwinism refers to the view
that evolutionary change is caused exclusively by natural selection, el
Synthetic Theory “includes modern genetics, population genetics, systemat-
circuitos integrados, and theories of speciation and macroevolution (based on paleontology,
comparative morphology, and developmental biology)", as well as factors
other than selection, including isolation, drift, and population size (Reif
et al., páginas. 43–44). On their account, both the Synthetic Theory and neo-
Darwinism are stages in the historical development of evolutionary theory,
and the Synthesis is different from its result, the Synthetic Theory. Neo-
Darwinism, coined in 1895 by George Romanes, predates the Synthetic
Teoría, which originated in the early 1930s (Reif et al., pag. 43).

Amundson’s portrayal of neo-Darwinism does not coincide with the
Romanesian description from Reif et al., though Amundson does emphasize
the role of adaptationism and natural selection in neo-Darwinian thinking
(Por ejemplo, pag. 164). But perhaps more important for the present purpose
of ﬂeshing out Amundson’s take on neo-Darwinism as a general way of think-
ing about evolution instead of as a more concrete theory, Amundson does
not mention Reif et al.’s discussions of potential identifying criteria of a con-
temporary synthetic evolutionary theory, difﬁculties associated with these
criteria, or their proposal of a structuralistic concept of the Synthetic Theory
and its advantages (Reif et al., páginas. 56–58). Reif et al. provide an argument for
a way to understand the result of the Synthesis as a kind of scientiﬁc theory,
and Amundson does not mention it. This is important because Amundson
does rely upon the authors’ discussion of what they refer to as “the essential
ﬁve components of the Synthetic Theory” (Reif et al. pag. 58, énfasis añadido),
the “relevant components [eso] follow naturally from this basic structure”
(Reif et al., pag. 59), and what “the Synthetic Theory rejects” (pag. 59, emphasis
added). Sin embargo, Amundson uses this part of Reif et al.’s argument to
elucidate what he believes are aspects and commitments of the Synthesis
sí mismo. Reif et al. are clear that they believe there is a difference between
the Synthesis, the resulting Synthetic Theory, and neo-Darwinism, pero
Amundson describes Synthesis commitments, and ultimately neo-Darwinian

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250

Neo-Darwinism and Evo-Devo

thinking, by co-opting their discussion of the Synthetic Theory. So, no
only do Amundson and Reif et al. deﬁne neo-Darwinism differently, pero
Amundson avoids all talk of Reif et al.’s conception of the Synthetic Theory
of Evolution in favor of a less restricted, broader-ranging account of neo-
Darwinian thinking that is, nonetheless, based on Reif et al.’s description
of a particular way of understanding what they take to be the Synthetic
Teoría.

Amundson’s use and discussion of Reif et al., I believe, serves as further
evidence that his description of neo-Darwinism is of a way of thinking about
or an approach to understanding evolution, not a particular kind of scientiﬁc
theory. I do not mean to suggest that Amundson unfairly uses Reif et al. o
that he mischaracterizes their claims; I do not think that is the case. Más
accurately, Amundson characterizes neo-Darwinism, en parte, by way of Reif
et al.’s discussion of what they refer to as the Synthetic Theory of Evolution
while at the same time avoiding reference to an evolutionary theory himself.
More simply, Amundson agrees with Reif et al.’s description of the results
of the Synthesis but does not describe these results as comprising a speciﬁc
evolutionary theory. En cambio, Amundson depicts the concepts, implications,
and rejections that were, according to Reif et al., the results of the Evolu-
tionary Synthesis as comprising a general neo-Darwinian view of evolution.
Using Reif et al., Amundson claims that ﬁve central concepts of the
Synthesis and the neo-Darwinian view are: 1) “mutations (random with
respect to adaptation); 2) “selection as the primary directional force (y
largely restricted to the individual level)"; 3) “recombination in sexually
reproducing populations”; 4) “isolation (various mechanisms preventing
gene ﬂow)"; y 5) “drift (the importance of which depends on effective
population size)" (pag. 165). Again following Reif et al., Amundson states that
the implications that follow from these concepts and are important for
understanding the Synthesis are: 1) “Speciation is predominantly allopatric
or parapatric”; 2) “Evolution is gradual but can have a wide range of
velocities”; y 3) “‘Developmental, historical and constructional constraints
limit the opportunism of evolution to a certain degree, but do not lead
to non-adaptive evolution’” (165). The Synthesis forbids, according to
Amundson via Reif et. Alabama., that “genetic factors are macromutations (ver,
p.ej., Goldschmidt 1940) and Lamarckian inheritance” and ‘“Baupläne’ or
types as actors in evolution” (Amundson p. 166).

Preceding this characterization of the Synthesis, Amundson devotes a
chapter to various responses to the Synthesis from more developmentally
inclined biologists. Amundson is careful, and correct, to point out that
there was some interest in developmental studies around and during the
time of the Synthesis. Aquí, Amundson cites T. h. Morgan’s eventually
abandoned symbolism that was developed in order to keep track of those

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Perspectives on Science

251

genes that were thought to “developmentally inﬂuence a trait” (pag. 189).
Sewall Wright, recognized as a member of the inaugural generation of
population geneticists and as a pivotal contributor to the Synthesis, era
also considerably interested in development. Amundson discusses Wright’s
interest in the inﬂuence of cytological factors on heredity (Wright 1941),
but Wright’s focus on pleiotropy, which stemmed from his work in both
population genetics and physiological genetics, is also noteworthy. Para
ejemplo, in Evolution and the Genetics of Populations (1968), Wright fol-
lows a section titled “The Developmental Process” with the claim that
the “netlike relationship between genome and complex characters” leads
to the generalizations that most character variations are affected by multiple
loci and that a gene replacement can affect multiple characters (páginas. 59–60).
Wright refers to these generalizations as the multiple factor hypoth-
esis and the principle of universal pleiotropy, respectivamente. Sin embargo,
Amundson argues that the developmental interests of those active during
this time did not affect the insigniﬁcant role of development during the
Synthesis (pag. 191).

Minelli (2010), an active evo-devo researcher, characterizes neo-Darwinism
in much the same way as Amundson. Minelli notes that the term originally
referred to the view that natural selection was the sole cause of evolutionary
cambiar, but because of the changes and advances that took place during
the Modern Synthesis, neo-Darwinism no longer refers to this view. Su
2010 paper begins with the statement that “There are brands of scientists
who should ﬁnd it intrinsically difﬁcult to identify their views, or those of
their colleagues, with a frozen set of tenets. These scientists specialize in the
study of change […]" (pag. 213). Before his more detailed description of neo-
Darwinism, Minelli states

In the context of the debate about the challenge evolutionary
developmental biology may offer to the neo-Darwinian view of
evolution, the problem cannot be seriously attacked by limiting the
comparison to sets of speciﬁc statements expressed by individual
científicos, in either camp at some speciﬁed time, along the evolution
of their personal thought. En efecto, it would be dangerously restrictive
even to extract deﬁnitive sets of principles from mainstream
textbooks or current research practice to be aseptically compared.
Específicamente, it can be seriously doubted whether the history of the
disciplines relevant to our discussion can really offer evidence for
neatly deﬁned alternative paradigms and neatly deﬁned revolutions.
(2010, pag. 214)

Like Amundson, Minelli does not explain neo-Darwinism as a kind of
scientific theory with an identifiable theoretic structure. En efecto, Minelli goes

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252

Neo-Darwinism and Evo-Devo

so far as to say that attempting such an explanation would be “dangerously
restrictive”. The language that he uses to define neo-Darwinism is much
the same as Amundson’s; Minelli describes neo-Darwinism as a kind of
“view of evolution”, a “framework” (p.ej., pag. 220), “tradition” (p.ej., pag. 221),
and “approach” (p.ej., pag. 222) to explaining and understanding evolutionary
phenomena.

Minelli claims that neo-Darwinism is a view that grew increasingly
focused on the adaptive results of natural selection acting on heritable var-
iations, a reductionist view further entrenched by geneticist Theodosius
Dobzhansky’s widely inﬂuential 1937 claim that evolution is change in
the genetic compositions of populations (pag. 216). Neo-Darwinian thinking,
for Minelli, explains adaptive change by way of the statistical models of
population genetics, which became the explanatory foundation of neo-
Darwinism. Despite the “broad absence” of development from neo-
Darwinism, Minelli correctly argues that some neo-Darwinists, particularly
j. B. S. Haldane, Julian Huxley, and Gavin R. de Beer, were very much
interested in the intersection of development and evolution (páginas. 214–215).
Others, including Amundson as discussed above, have argued similarly that
development was not completely absent from neo-Darwinist thinking (p.ej.,
Burian, Gayon, and Zallen 1991; allen 2007; Dietrich 2011).

Pigliucci and Müller (2010), sin embargo, present a different take on neo-
Darwinism. Pigliucci, who has Ph.D.s in both biology and philosophy,
and Müller, an evo-devo practitioner, make it clear that, on their view,
neo-Darwinism helped set the intellectual stage for the Modern Synthesis
of the twentieth century (pag. 6). For these authors, neo-Darwinism refers
to the resurgence of the Darwinian view that natural selection is the pri-
mary cause of evolutionary change and is “not to be confused, as it so
often is, with the Modern Synthesis” (pag. 5). They explain that Romanes
coined the term neo-Darwinism to mock Alfred Russel Wallace’s and August
Weismann’s pan-selectionist responses to various evolutionary alternatives
to Darwinian natural selection promoted after the publication of On the
Origin of Species in 1859. They explain further that into the twentieth cen-
tury, this brand of neo-Darwinism was thought to conﬂict with Mendelism,
the view that Mendel’s recently rediscovered transmission work ruled out
gradual selection of small variations, and it was this perceived conﬂict be-
tween neo-Darwinism and Mendelism that led to the Modern Synthesis
(páginas. 5–6).

The Modern Synthesis, according to Pigliucci and Müller, is “the concep-
tual framework that has deﬁned evolutionary theory since the 1940s” (pag. 3)
that resulted from the dismantling of the Mendelian/neo-Darwinian conﬂict
by population genetics and the “understanding and acceptance of population
genetics by the majority of practicing evolutionary biologists” that followed

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(pag. 6). They ﬂesh out what they refer to as the Modern Synthesis “conceptual
framework” with Douglas Futuyma’s (1986) summary.

Perspectives on Science

253

The major tenets of the evolutionary synthesis, entonces, were that
populations contain genetic variation that arises by random
(es decir., not adaptively directed) mutation and recombination; eso
populations evolve by changes in gene frequencies brought about by
random genetic drift, gene ﬂow, and especially natural selection;
that most adaptive genetic variants have individually slight
phenotypic effects so that phenotypic changes are gradual (a pesar de
some alleles with discrete effects may be advantageous, as in
certain color polymorphisms); that diversiﬁcation comes about by
speciation, which normally entails the gradual evolution of
reproductive isolation among populations; and that these processes,
continued for sufﬁciently long, give rise to changes of such great
magnitude as to warrant the designation of higher taxonomic
niveles (genera, familias, Etcétera). (From Pigliucci and
Müller 2010, pag. 9)

Pigliucci and Müller claim that the Modern Synthesis framework is restricted
by the assumption of population genetics models that genetic variation is
continuous and small (gradualism) (pag. 13). The framework is further re-
stricted by its commitment to externalism, or the view that the external
process of natural selection is primary (pag. 13), and gene centrism, the view
that the gene is the only source of heritable variation (pag. 14).

How does Pigliucci and Müller’s view compare to those of Amundson
and Minelli? Amundson and Minelli agree that the neo-Darwinian frame-
trabajar 1) is founded on population genetic models of the maintenance and
reﬁnement of gene frequencies in populations through generations; 2)
recognizes natural selection as the primary cause of evolutionary change;
y 3) does not include developmental input. And though Piglucci and
Müller’s description of neo-Darwinism differs from those of Amundson
and Minelli, Pigliucci and Müller’s account of the framework developed
during the Modern Synthesis is very much like Amundson’s and Minelli’s
accounts of neo-Darwinism. So, for present purposes, I replace Pigliucci
and Müller’s take on neo-Darwinism with their account of the Modern
Synthesis framework; nonetheless, it should be noted that Pigliucci and
Müller adopt Romanes’ original concept of neo-Darwinism and are clear
that it ought not be confused with the Modern Synthesis.

Laubichler’s description of neo-Darwinism is a departure from each of the
accounts discussed so far. Unlike other participants in the debate of interest
aquí, Laubichler claims that as a conceptual framework, neo-Darwinism is
a gene-centered Kuhnian paradigm (páginas. 199–200). He does not expand on

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254

Neo-Darwinism and Evo-Devo

the nature of a Kuhnian paradigm, a notoriously problematic concept (p.ej.,
Lakatos and Musgrave 1970; Masterman 1970; Laudan 1984), but he does
argue that evo-devo represents what he refers to as a counter-revolutionary
paradigm shift away from the neo-Darwinian paradigm that is roughly
Kuhnian in nature (pag. 200). What makes this so-called counter-revolution
different from a Kuhnian revolution is the return to a more Darwinian broad
understanding of phenotypic evolution.

On Laubichler’s view, neo-Darwinism treats phenotypes more narrowly,
as epiphenomenal results of interactions between genes and populations,
which are fundamental within the neo-Darwinian framework. The statis-
tical models of population genetics are fundamental to neo-Darwinism as
well since they model the dynamic effects of various conditions and pop-
ulation structures on genes. According to Laubichler, neo-Darwinism does
not include a mechanistic account of the relations between genotypes and
phenotypes because such an account requires developmental input; neo-
Darwinism considers development as something that is irrelevant to the
dynamic interactions that affect genetic maintenance and reﬁnement in
populations and, entonces, is unable to mechanistically explain phenotypic evo-
lution (pag. 201). Like the others, aunque, Laubichler acknowledges that
some neo-Darwinists included development in their studies of evolution
(pag. 202). Asimismo, Laubichler acknowledges the successes of neo-Darwinism.
In particular for him, the mathematical models of population genetics
boosted evolutionary biology to the ranks of an exact science, and neo-
Darwinism has provided fruitful insights into genetic variation, speciation,
and population dynamics (pag. 200).

There are good reasons to ignore Laubichler’s appeal to Kuhnian para-
digms. Primero, he does not elaborate on the concept despite the many well-
known criticisms of Kuhn’s discussion of paradigms in The Structure of Scientiﬁc
Revolutions ([1962] 2012). En efecto, Margaret Masterman identiﬁed twenty-
one different uses of paradigm by Kuhn in Structure (Masterman 1970). Kuhn
subsequently acknowledged his ambiguous use of the term and continued
to rework the concept of a scientiﬁc paradigm late into his career. Para el
claim that neo-Darwinism is a Kuhnian paradigm to be taken seriously in
light of well-known and arguably devastating criticisms, the concept of a
Kuhnian paradigm must be clariﬁed. That Laubichler did not do this indi-
cates, most charitably, that the claim can be ignored for the present purpose
of ﬂeshing out neo-Darwinism.

A second reason to ignore Laubichler’s appeal to Kuhnian paradigms is
that he weakens his thesis that evo-devo represents a Kuhnian-like “counter-
revolution” in relation to neo-Darwinism by pointing to the successes of neo-
Darwinism. He claims that neo-Darwinism, with its abstraction of phenotypes
and genes, led to conceptual innovations that “were a major theoretical

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Perspectives on Science

255

breakthrough” (pag. 200). He goes on to say that the combination of mathemat-
ical population genetics models with empirical studies “was no small accom-
plishment” because it allowed for both the theoretical and empirical study of
parts of the evolutionary process. This “ﬁrmly established evolutionary biology
as an exact science” (pag. 200) and was supported further by the insights of
molecular biology regarding the population genetics concepts of gene, allele,
and mutation (pag. 201). Laubichler’s own description of the successes of neo-
Darwinism indicates that evo-devo does not represent anything like a Kuhnian
revolution since a Kuhnian revolution is the wholesale replacement of one
paradigm by another. Since Laubichler acknowledges that evo-devo does not
replace neo-Darwinism, neo-Darwinism need not be described as a Kuhnian
paradigma, not even for argumentative purposes.

Based on the accounts of the participants of the current debate, entonces, neo-

Darwinism is, apenas, como sigue:

Neo-Darwinism: An explanatory framework, way of thinking
acerca de, or approach to understanding and explaining evolution
that is founded on the mathematical models of population genetics
that model the dynamic effects of mutation, migration, drift,
and natural selection on gene frequencies in populations over
generational time and include abstract and limited concepts of
genes and phenotypes; natural selection is understood to be the
primary cause of adaptive evolutionary change narrowly deﬁned
as change in gene frequencies in populations; changes above the
species level are the results of the processes modeled by population
genetics over a sufﬁciently long time span; ontogenetic processes
that bridge genotypes and phenotypes are set aside as irrelevant
to explanations of evolutionary change.

Part of the difficulty of assessing whether neo-Darwinian thinking and evo-
devo are compatible and, further, whether the two can be successfully merged
into a synthetic theory of evolution is defining neo-Darwinism. The term has
its own historical lineage that dates back to the late 19th century, to the days
of Romanes, Wallace, and Weismann, y qué, exactly, the term refers to
has been muddied by more than 100 years of intellectual efforts in evolu-
tionary biology. Neo-Darwinism has become closely associated with the
Modern Synthesis, but the Modern Synthesis is itself a fuzzy target that
many different authors have described in many different ways. My goal,
sin embargo, is to investigate and strengthen the current debate, not to pro-
vide a deﬁnitive account of neo-Darwinism. Toward this end, I have pro-
vided analysis of the term as it is used by Amundson, Minelli, Pigliucci
and Müller, and Laubichler, and I believe that I have provided a deﬁnition
of neo-Darwinism that generally ﬁts the ways in which the term is used in

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256

Neo-Darwinism and Evo-Devo

this debate. The question of whether neo-Darwinism so-deﬁned accurately
reﬂects current evolutionary biology is a different, albeit important and
interesante, pregunta.

2.2 Evo-Devo Deﬁned
Fortunately, less work is required to ﬁnd consensus among these authors on
the nature of evo-devo. Amundson is clear that while the dramatic growth
of molecular biology, speciﬁcally molecular developmental genetics during
the 1990s, transformed interest in the connection between ontogeny and
phylogeny, the interest itself is not new (pag. 1). De hecho, interest in the relation-
ship between development and evolution precedes Darwin. Pero, descubrimientos
of highly evolutionarily-conserved Hox genes and other genetic homologies
in very distantly related species renewed this interest with an unprecedented
molecular perspective. Hox genes, que contienen un 180 base pair sequence
called a homeobox, play important causal roles during development. El
homeobox codes for a 60 amino acid protein sequence, the homeodomain,
that binds with speciﬁc DNA sequences to regulate gene expression during
the course of embryogenesis and are causally efﬁcacious in the production
of identiﬁable phenotypic units (Burian 2005b, pag. 215). Differently put,
Hox genes encode proteins that help regulate when and where speciﬁc
morphologically important proteins are synthesized during development
of the embryo. Through protein sequencing and molecular comparisons, él
was conﬁrmed that incredibly morphologically diverse organisms, como
Drosophila, or fruit ﬂies, and humans, have Hox genes with stunningly similar
homeoboxes. Despite our dramatic morphological differences, Hox genes
serve as evidence of our evolutionary relatedness with Drosophila (pag. 5).
Evo-devo explains away the initial paradox by way of a complex gene regu-
latory network. Phenotypic evolution proceeds, en parte, by way of changes
in the regulation of gene expression during development.

With the insights from molecular developmental genetics, Amundson
claims that the contemporary ﬁeld of evo-devo aims to explain “evolution
as the modiﬁcation of developmental processes” (pag. 247) that involve
interactions between genes that work as a kind of network within a develop-
mental system; evolutionary change takes place when the network is modi-
ﬁed, resulting in changes in form (pag. 7). In contrast with neo-Darwinism,
“[mi]vo-devo advocates merely believe that additional mechanisms, mecha-
nisms involved with ontogeny rather than population genetics, must con-
tribute to a full understanding of evolution” (pag. 3). For Amundson, entre
the explanatory themes of evo-devo that are not part of neo-Darwinism are
innovation (pag. 245), homology (pag. 241), modularity (pag. 244), and evolvability
(pag. 244). The emphasis on these concepts illustrates that evo-devo breathes

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Perspectives on Science

257

new life into the long-standing problems tied to the crossroads of develop-
ment and evolution.

Similarmente, Minelli claims that a deﬁning feature of evo-devo is its focus
on the ability (or inability) of a system to generate alternative heritable
fenotipos, or the evolvability of a trait. He states, “In fact, evo-devo pro-
vides its unique contribution to understanding the evolutionary process by
a description and analysis of developmental constraint and its elements”
(pag. 218). For Minelli, evo-devo is a research ﬁeld separate from develop-
mental biology and evolutionary biology, but it remains related to those
ﬁelds through investigation of questions, like evolvability, that are of in-
terest to both and through use of investigative tools from both (pag. 220).
Pigliucci and Müller largely agree with Amundson and Minelli. Ellos
claim that evo-devo has developed as a ﬁeld in its own right since the
1980s because of questions concerning phenotypic evolution that remained
unanswered by the Modern Synthesis framework (pag. 4). They argue that
evolutionary theory needs this growing ﬁeld because embryology and devel-
opmental biology did not play a role in the Modern Synthesis, y, entonces, el
resulting explanatory framework cannot explain some evolutionary phenom-
ena. More speciﬁcally, evo-devo eases the restriction of the framework’s
commitment to externalism by providing insights into the role of develop-
mental processes and systems on phenotype speciﬁcity (pag. 13). That evo-devo
needs to be included in evolutionary theory because of evolutionary theory’s
explanatory restriction is, para ellos, “obvious and largely undisputed” (pag. 8).
If we overlook Laubichler’s Kuhnian language once again, his account of
evo-devo is consistent with those of Amundson, Minelli, and Pigliucci and
Müller. On Laubichler’s account, evo-devo is comprised of multiple research
programs and explanatory structures united in their pursuit of a mechanistic
theory of phenotypic evolution (pag. 201). De nuevo, Laubichler argues that the
phenotype concept of evo-devo is importantly different from the narrow con-
cept of the phenotype emphasized by neo-Darwinism. He contends that
phenotypic evolution and innovation, the core of evo-devo, rest upon an
understanding of the phenotype that incorporates a broad range of causal
mechanisms, including gene regulation, from various levels of biological
organization and temporal scales (pag. 203). Eso es, the phenotype of evo-
devo is the dynamic result of a host of molecular, developmental, physiological,
and environmental causal mechanisms across developmental, generational,
and geologic time. A mechanistic theory of phenotypic evolution, entonces, requires
much more than what is offered by the statistical models of population
genetics, y, according to Laubichler, it is likely that evo-devo has the tools
to provide such a theory.

En efecto, within the current debate, there is little disagreement over the
nature of evo-devo. All agree that evo-devo provides unique explanations

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258

Neo-Darwinism and Evo-Devo

of evolutionary phenomena that are left unaddressed by the neo-Darwinian
acercarse. The consensus is that the phenotype concept foundational to
evo-devo is broader and less abstract than that of neo-Darwinism. En cambio
of thinking of phenotypes merely as gene products and black-boxing the
descansar, evo-devo conceives of phenotypes as the results of complex arrays of
developmental processes that involve very speciﬁc entities and interactions
at multiple levels of biological organization. Evo-devo aims to explain the
evolution of phenotypes so deﬁned, unlike neo-Darwinism, cual, accord-
ing to these authors, generally aims to explain changes in the genetic com-
positions of populations. These authors also agree that evo-devo is partially
deﬁned by the emphasis placed on the explanatory role of concepts such
as evolvability, innovation, modularity, and regulation. Arguably, estos
concepts have little or no role in the neo-Darwinian approach because of
the insigniﬁcant role of embryology and developmental biology during the
Modern Synthesis.

So, evo-devo, as a term in the current debate, is generally understood in

the following way:

Evo-devo: A scientiﬁc ﬁeld of study that emerged during the
last decades of the twentieth century to explain evolutionary
phenomena not explained by neo-Darwinism because of the
lack of embryological and developmental input during the
Modern Synthesis; evo-devo aims to explain phenotypic evolution,
where phenotypes are understood to be the effects of complex,
multi-level causal processes, and these explanations incorporate
the biological concepts of evolvability, innovation, modularity,
regulación, y otros.

2.3 The Arguments
There are two prominent, if general, camps in the current debate. On one
side are those who claim that neo-Darwinism and evo-devo are compatible
y, entonces, some kind of synthesis is possible. Minelli and Pigliucci and Müller
most clearly fall into this camp. Minelli argues that evo-devo’s unique focus
on evolvability does not conﬂict with the neo-Darwinian framework since
evolvability is “amenable to” or at least partially deﬁned by neo-Darwinian
conceptos (pag. 218). Evolvability understood as “the ability of a genetic system
to produce and maintain potentially adaptive genetic variants” (pag. 219)
importantly involves heritable genetic variation and selection, the two
major components of neo-Darwinian thought. Evo-devo expands the neo-
Darwinian framework by including the developmental processes that lie
between genotypes and phenotypes as objects of investigation relevant to
evolvability (pag. 220). He explains that the “evo-devo perspective” constitutes

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Perspectives on Science

259

a “conceptual advance” in that it examines phenotypes and genes from the
joint perspective of development and evolution. Minelli states, “By focusing
on evolvability, evo-devo does not disrupt the neo-Darwinian view of evolu-
ción, as a process of change based on variation and selection (plus drift).
Bastante, it shows what can be gained by avoiding the myopic identiﬁca-
tion of variation with allelic differences only” (pag. 220). En efecto, for Minelli,
the unique perspectives and explanations offered by evo-devo “may well be
described as extending or complementing” the neo-Darwinian view.

Both Pigliucci (2007, 2009) and Müller (2007) have argued indepen-
dently that the concepts emphasized by evo-devo research (p.ej., evolvability,
phenotypic plasticity, emergence, epigenetic traits, and organization) en
pursuit of a mechanistic explanation of phenotypic evolution do not con-
tradict or challenge traditional evolutionary theory. En cambio, these concepts
and related research work to explain previously unexplained evolutionary
phenomena, thereby extending the explanatory framework developed during
the Modern Synthesis.4 Their collaboration, Evolución: The Extended Synthesis
(2010), is devoted to what they refer to as the ongoing Extended Synthesis
of evolutionary biology, the offspring of the Modern Synthesis. Aquí, ellos
claim that insights from molecular genetics and genomics, así como el
concepts of epigenetics, plasticity, environmental factors, and innovation,
were not part of the Modern Synthesis (pag. 12). As these ﬁndings and con-
cepts continue to gain more attention, what is currently taking place,
according to them, is a shift away from statistical population dynamics
toward a causal-mechanistic account of evolution that takes organismal pheno-
typic change out of the black box in which it was previously placed. Este
shift, Pigliucci and Müller claim, “brings with it a signiﬁcantly expanded
explanatory capacity of evolutionary theory” (pag. 12).

Amundson straddles the two camps in the contemporary debate. Él
claims that evo-devo, which is fundamentally concerned with evolutionary
changes in morphologies or developmental types, and neo-Darwinism,
which is fundamentally concerned with evolutionary changes in genes
in populations, are “deeply inconsistent” (pag. 225). Para él, the ontologies
and explanatory aims of evo-devo and neo-Darwinism are severely at odds

4. In direct response to Pigliucci and Müller, I have argued elsewhere (2010, 2011) eso
it is incorrect to describe the ongoing changes as an extension of the Modern Synthesis
estructura. The Extended Synthesis view offered by Pigliucci and Müller and endorsed,
perhaps weakly, by Minelli is incorrect in large part because the concepts highlighted by
evo-devo research pose serious conceptual challenges to the foundation of the Modern Syn-
thesis framework, population genetics. While it is certainly true that previously unan-
swered questions about the origination of novel phenotypes and the evolution of
morphological diversity can now be addressed, Pigliucci and Müller fail to adequately de-
scribe the current episode of change as an extension of the Modern Synthesis framework
given that framework’s population genetics foundation.

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with one another. Amundson argues that if a synthesis of the two is possible,
either the population thinking of neo-Darwinism must weaken in order to
allow room for developmental types, or the developmental types of evo-devo
must be redeﬁned in a way that makes them applicable to population think-
En g (páginas. 256–7). Despite this, Amundson is (muy) cautiously optimistic in
his conclusion. He admits that it is probably the case that there is a more
moderate path between these two options, though he does not see a clear
way to dismantle the dichotomous conﬂicts between evo-devo and neo-
Darwinism. Still, Amundson is hopeful that the continued success of both will
illuminate their compatibility and the path toward a new synthesis (pag. 257).
Laubichler represents the opposing camp by arguing that evo-devo
signiﬁcantly challenges neo-Darwinian thinking on conceptual grounds.
This conceptual challenge is two-fold: 1) at the core of evo-devo is a more
inclusive concept of the phenotype than that of neo-Darwinism; y 2)
alongside the broader phenotype concept are concepts that are either
original to or crucially transformed by evo-devo’s organism-based approach.
The latter include regulatory networks and their evolution, modularity,
plasticity, and innovation (pag. 204). Evo-devo’s conceptual challenge to neo-
Darwinism, entonces, takes the form of a causally complex mechanistic approach
to phenotypic evolution grounded in concepts that are integral to organismal
developmental processes rather than the “conceptual abstractions of ‘gene’
and ‘population’” (pag. 209) of gene-centric neo-Darwinism.

In terms of this debate, there is at least one thing upon which all of the
participants agree: both neo-Darwinism and evo-devo, two different, evi-
dentially supported explanatory apparatuses, explain or account for different
evolutionary phenomena. Eso es, both explanatory frameworks, with their
different concepts and focuses, are applicable to the study and explanation
of evolutionary changes. In what remains, I argue that this indicates that
there is a relative signiﬁcance issue between neo-Darwinism and evo-devo.
Differently put, I contend that the applicability of these two different ex-
planatory frameworks to different evolutionary phenomena demonstrates
that there is a relative signiﬁcance issue here, which suggests further that
both neo-Darwinism and evo-devo will continue to develop as different
frameworks rather than participate in a theoretical synthesis. Though it has
been overlooked until now, this line of argument is supported by the terms
and arguments of this debate as they have been developed by these authors.
Primero, in section three, I expand upon the claim that neo-Darwinism and
evo-devo explain different evolutionary phenomena.

3. Different Phenomena Explained
A closer look at what is uncontroversially agreed upon, at least by those
involved in the current debate, to be the foundation of the neo-Darwinian

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Perspectives on Science

261

estructura, the models of population genetics, and evo-devo helps to show
that they explain different things. In section four below, I use this and the
work of John Beatty (1995, 1997) to argue that a relative signiﬁcance issue
exists between neo-Darwinism and evo-devo.

3.1 The Population Genetics Foundation of Neo-Darwinism
Between 1918 y 1932, population geneticists Ronald Fisher, Sewell
Wright, y j. B. S. Haldane developed the statistical models needed to
explain the dynamic effects of mutation, migration, drift, and natural selec-
tion on gene frequencies of actual populations over generational time, thereby
demonstrating the compatibility of Mendelian inheritance and Darwinian
natural selection (p.ej., Provine 1971; Lewontin 1980; Beatty 1986; Ridley
2004; Millstein and Skipper 2007). Simplemente pon, these statistical models, accord-
ing to William Provine, demonstrated how mutation, migration, drift, y
natural selection could account for evolution (1980, pag. 55). En efecto, Provine
(1971) claims that Fisher, Wright, and Haldane did more than develop
theoretical population genetics—they were the architects of the Modern
Synthesis, during which they succeeded in quantitatively synthesizing
Mendelian heredity, Darwinian selection, and statistical methods through
the development of population genetics models (139–140). Sin embargo,
Provine later admitted that his initial description of the Modern Synthesis
was inaccurate, y, in response, he argues that the Modern Synthesis
is more accurately described as an “evolutionary constriction” (1989, pag. 165).
Provine (1989) claims that the Modern Synthesis was a time during which
biologists from various ﬁelds winnowed down non-Darwinian alternatives
(pag. 176) because the mathematical and theoretical works of Fisher, Wright,
and Haldane clearly showed that evolution could be explained with rela-
tively few variables, far fewer variables than biologists had ever anticipated.
It was during the Modern Synthesis that constriction based on the tools of
population genetics spread throughout the study of evolution, and popula-
tion genetics resulted in “a new way of seeing evolutionary biology” (pag. 177).
Fisher’s most detailed explication of his general theory of evolution,
which I refer to as his Genetical Theory of Natural Selection (GTNS)5, es
found in his book of the same name, The Genetical Theory of Natural Selection
([1930b] 1958a). Aquí, Fisher relies on an analogy with statistical mechanics
to demonstrate the relationship between Darwinian natural selection and
Mendelian inheritance. Fisher’s particular aim was to explain how natural
selection affects evolutionary change in populations given the principles of
Mendelian inheritance (Pescador 1930; Skipper 2002, pag. 343). The details of
Fisher’s GTNS remain a topic of debate over 80 years after the publication

5. This abbreviation comes from Skipper (2002, pag. 342).

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Neo-Darwinism and Evo-Devo

of the ﬁrst edition of his treatise. Por ejemplo, papers by George Price
(1972), Warren Ewens (1989), Anthony Edwards (1994), Anya Plutynski
(2006), and Robert Skipper (2007) each argue for a particular interpreta-
tion of Fisher’s “Fundamental Theorem of Natural Selection,” which Fisher
discusses in chapter two of The Genetical Theory of Natural Selection.

Generally, Fisher’s GTNS is understood as follows:

GTNS: Evolution occurs in large, randomly mating or panmictic
populations and is driven primarily by natural selection, or mass
selección, at low levels acting on the average effects of single allele
cambios (of weak effect) at single loci independent of all other loci
(Skipper 2002, pag. 343).6

As the GTNS illustrates, Fisher believed evolutionary phenomena take place
in large populations where mating is random. All evolutionary change is
primarily the result of natural selection, which acts upon allelic variation
supplied by mutation.

Wright’s earliest presentations of what he referred to as the Shifting
Balance Theory (SBT) are his highly mathematical long paper of 1931
and its non-technical 1932 complement (Wright 1931, 1932; Skipper and
Dietrich 2012, pag. 16). In his four-volume Evolution and the Genetics of Popula-
ciones (1968, 1969, 1977, 1978), Wright further develops his SBT. Through-
out the course of his work, Wright describes the goal of his SBT in various
maneras. En 1931 y 1932, Wright claimed the goal of the SBT was to explain
the ideal conditions needed for evolutionary change. Por 1978, sin embargo,
Wright strengthened this claim, stating that the SBT explained the “prin-
cipal process by which cumulative evolutionary change occurred in nature”
(Skipper 2002, 344). Wright readopted his statement from the 1931 y
1932 documentos, once again claiming the goal of his SBT was to explain the ideal
conditions required for evolution to take place (Skipper 2002; Skipper and
Dietrich 2012).

To illustrate the three phase shifting balance process through which Wright
believed evolution proceeded, he graphically depicted a two-dimensional
metaphorical adaptive landscape that has become one of the most inﬂuential
diagrams in evolutionary biology (Dietrich and Skipper 2012; Skipper and
Dietrich 2012; for Wright’s adaptive landscape ﬁgures, ver figura 1 en el
end of this article). The diagram represents possible gene combinations along
with their adaptive values. The contour lines of the diagram depict the “hilly”

6. As Skipper (2002) points out, this summary of the GTNS “has remained essentially
unchanged for the last 70 years” (pag. 344). While some of the details of Fisher’s GTNS, semejante
as the Fundamental Theorem, still foster debate over the correct interpretation, this summary
of the GTNS is fairly uncontroversial.

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Figure1. Wright’s adaptive landscape ﬁgures (Wright 1932: 358, 361).
1A represents possible gene combinations and their respective adaptive values. 1B
represents evolution on the landscape of 1A under different conditions. In A–E,
the intensity of selection (s) and rate of mutation (tu) vary, as does population
tamaño (norte, nm). The view that Wright explains in the SBT is represented by F.

264

Neo-Darwinism and Evo-Devo

surface of the landscape due to the epistatic relations between genes. El
adaptive “peaks” of the landscape, designated by “+”, represent possible gene
combinations with high adaptive value. The adaptive “valleys”, designated by
“−”, represent possible gene combinations with low adaptive value. Wright
was clear that due to the number of possible gene combinations, the actual
population genetics of how evolution proceeds would require a diagram de-
picting several thousand dimensions (Wright 1932; Skipper 2002, pag. 344;
Dietrich and Skipper 2012).

Wright used his adaptive landscape to describe what he believed were the
ideal conditions for a population to reach the optimal adaptive peak. Idealmente,
peak shifts take place in three stages or phases, according to Wright. Primero,
genetic drift, typically maladaptive, moves semi-isolated subpopulations
into adaptive valleys. In this ﬁrst phase, drift changes the gene frequency
distribution of subpopulations in such a way that subpopulations lose ﬁtness,
thus landing them in adaptive valleys. Segundo, within the subpopulations,
mass selection acts to move subpopulations to adaptive peaks and out of
adaptive valleys. In this second phase, mass selection changes the gene fre-
quency distributions of subpopulations in such a way that the ﬁtnesses of
those subpopulations is raised, thus pushing them from adaptive valleys
to adaptive peaks. Tercero, differential dispersion, or the migration of some
members of more ﬁt subpopulations to less ﬁt subpopulations, drives inter-
demic selection, or selection between subpopulations, which pulls the global
population up its optimal peak. In this third phase, interdemic selection
changes the gene frequency distribution of the global population in such
a way that the ﬁtness of the entire population is raised.

As the foundation of neo-Darwinism, Fisher’s GTNS and Wright’s SBT
illustrate the kinds of evolutionary phenomena explained by the framework.
Fisher and Wright both provided mathematical models that attempt to
explain how dynamic microevolutionary processes and population size and
structure cause evolutionary change where evolutionary change is deﬁned as
change in the genetic compositions of populations. The models of population
genetics provided the theoretical and statistical tools needed to investigate the
possible causes of evolutionary change in different kinds of actual populations.

3.2 Evo-Devo Research
Evo-devo is partially comprised of several areas of research, many of which
superposición. Müller (2007) provides an introduction to predominant areas of
research within the ﬁeld. A quick look at these research areas sheds light
on the phenomena explained by evo-devo.

One predominant area of research within the ﬁeld of evo-devo integrates
comparative embryology, morfología, and genetics to focus on similarities
and differences at multiple levels of biological organization, from the genetic,

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molecular, and cellular levels up, in order to understand how the ontogenies
and morphologies of species have changed over time. Fossilized embryos
and other evidence from paleontology allows for comparison of the morpho-
genetic and embryological differences between primitive and extant species
(Müller 2007, pag. 943). Comparative genomics compares sequences, expres-
sion patterns, and gene products and interactions, which allows for compar-
ison of developmental sequences (Laubichler 2007, pag. 349). The comparative
approach provides evidence of signiﬁcant changes in developmental pathways
and morphologies in species over geologic time and provides evidence of
phylogenetic relationships. This particular area of research utilizes compara-
tive techniques to determine how aspects of development changed over
tiempo. Concepts and methodologies from paleontology, comparative em-
briología, comparative morphology, comparative genomics, and systematics
are integrated to better understand the evolution of developmental processes
and outcomes.

A second area of research within evo-devo focuses on the components
and interactions of both genetically determined and non-genetically de-
termined properties of developmental systems. What is of interest here
are the properties of development that are not controlled directly by genes,
such as self-organization, cell-cell signaling, and developmental timing,
and how these epigenetic factors inﬂuence evolutionary changes. Changes
in cell number or developmental timing can produce phenotypes found in
ancestral organisms (Alberch and Gale 1985). The aim of this research is
twofold. One goal is to better understand and explain the complex dy-
namics of development, as well as the effects of environmental inﬂuences
on developmental systems and resulting morphologies. A second goal of
this research is to understand and explain how particular changes to de-
velopmental systems can affect evolutionary change. Such research is closely
related to experimental embryology (Laubichler 2007, pag. 349), y por lo tanto
borrows methodologies and concepts from its predecessor. Also integrated
in this research are aspects of developmental genetics, systems biology,
epigenetics, and ecology.7

7. Laubichler (2007, pag. 349) and Müller (2007, pag. 943) distinguish this area of research
from what they both refer to as the evolutionary developmental genetics program. Both pro-
grams focus on components and interactions that comprise developmental processes; the only
difference I see is that Laubichler and Müller’s evolutionary developmental genetics program
does not include epigenetic or environmental factors. Fundamentally, sin embargo, I see no reason
to describe these as two different areas of research because the general focus of both is devel-
opmental systems. The researcher who focuses on developmental genes and the researcher who
focuses on epigenetic and environmental factors still share a common object of interest—
developmental systems. At any rate, nothing much hangs on Laubichler and Müller’s separa-
tion of these research areas.

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Another evo-devo area of research uses computational modeling and
simulation to relate changes at the genetic level to changes at the cellular
and tissue levels (Müller 2007, 943). Exciting results of this research
include the computational ability to reconstruct gene expression during
embryonic development in three-dimensions and the development of
a quantitative approach to model the trajectories of ontogenetic shapes
(Müller 2007, pag. 943). Müller claims that the theoretical tools utilized
in this research “help to localize the ontogenetic components of pheno-
typic change, assist in the organization of data and link evo-devo with
quantitative genetics and with the study of morphological integration”
(páginas. 943–4).

3.3 Explanatory Differences
The areas of research within evo-devo explain morphological, or phenotypic,
change within and across taxonomic levels over a range of time spans. Ex-
planations of this kind include the origin of novel morphologies and changes
in gene regulation, ontogenetic processes, and the diverse causally-relevant
components of those processes, p.ej., genes, molecular and environmental
signals, transcription factors. Each of the aforementioned areas of research
involve investigations of entities, activities, and the organization of those
entities and activities at multiple levels of biological organization, incluido,
al menos, the genetic, molecular, cellular, tejido, and organismal levels. No
particular level is privileged in evo-devo’s multi-level approach to mechanis-
tically explaining phenotypic change.

As characterized by the current debate, neo-Darwinism, en el otro
mano, explains the effects of microevolutionary processes, most particularly
natural selection, and population structures on the genetic makeup of organ-
ismal populations where phenotypes are narrowly thought of as a means of
tracking genes. Such explanations pay no signiﬁcant attention to the entities
and processes involved in individual development, and the general explana-
tory focuses are the genetic and populational levels. Perhaps most indicative
of the explanatory differences between neo-Darwinism and evo-devo are the
different ways in which the two treat the relations between genes and phe-
notypes. According to the debate of interest here, neo-Darwinism places the
causally complex processes of development that are the physiological links
between genes and phenotypes into a black box and sets that box aside as
explanatorily irrelevant while evo-devo takes the contents of the black box
and attempts a multifaceted explanation of its origin and subsequent evolu-
ción. More simply, evo-devo explains phenomena that are seemingly explan-
atorily irrelevant within the neo-Darwinian framework as that framework is
depicted by the current debate. The neo-Darwinian framework, absent sig-
niﬁcant embryological and developmental inﬂuence, explains populational

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Perspectives on Science

267

changes using a phenotype concept that allows for gene tracking through
generaciones.

Sin embargo, the phenomena explained by each are evolutionary phe-
nomena. Changes in and maintenance of the genetic compositions of
populations and heritable changes in morphologies and developmental
processes are ways in which biological entities, understood to include
super-organismic entities such as populations and species, are modiﬁed
in relation to their ancestors over time. Natural selection, mutation,
migration, drift, environmental factors, and heritability all play some role
in both kinds of changes. That neo-Darwinism and evo-devo explain
different evolutionary phenomena shows that evolutionary change is in-
deed heterogeneous. Eso es, not all evolutionary phenomena are the same;
evolution encompasses different phenomena that are explained by different
explanatory frameworks. This heterogeneity is apparent within the current
controversy—all engaged in it acknowledge, if only implicitly, that neo-
Darwinism explains some evolutionary phenomena and evo-devo explains
otros.

As I see it, this heterogeneity and the different explanatory frame-
works that explain different parts of it point to a relative signiﬁcance issue.
Además, I believe that the relative signiﬁcance issue suggests that both
of these explanatory frameworks will survive in evolutionary biology rather
than form a synthetic theory that explains all of the phenomena in the
heterogeneous domain. De nuevo, my claim that the relative signiﬁcance
issue indicates that both frameworks will continue to develop unsyn-
thesized says nothing of the possibility of a synthesis, and my claim need
not be interpreted as staking a claim on whether neo-Darwinism and
evo-devo are compatible. En cambio, my claim, built using the conceptual
tools of the ongoing debate, employs what is agreed upon within the
debate, a saber, that both well-supported frameworks explain different
evolutionary phenomena, to address what I take to be the true under-
lying concern of the debate: the likely direction of neo-Darwinism and
evo-devo.

4. Relative Signiﬁcance and Synthesis
Beatty, who introduced and expanded upon the nature of relative signiﬁ-
cance controversies in the 1990s, argues that a plurality of evidentially sup-
ported explanatory frameworks8 may be required to account for the different
phenomena that comprise heterogeneous scientiﬁc domains. En otras palabras,
it is sometimes the case that the evidence suggests that bodies of related but

8. Beatty uses theory, mechanism (p.ej., 1995, pag. 65), and models (p.ej., 1997, pag. S432) a

refer to those scientiﬁc constructs that account for items in scientiﬁc domains.

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268

Neo-Darwinism and Evo-Devo

different phenomena, or heterogeneous domains9, cannot be accounted for by
a single explanatory framework. In such a case, a relative signiﬁcance issue
may exist. Instead of taking issue with which framework is the ultimately
correct framework in a winner-takes-all scenario, debates over relative signif-
icance concern the signiﬁcance of one well supported framework relative to
the other(s) where signiﬁcance is assessed, apenas, in terms of “the propor-
tion of phenomena within the domain” that is correctly accounted for by
el marco (Beatty 1997, PAG. S432). Put differently, in domains where a
variety of phenomena are accounted for by a number of evidentially supported
frameworks rather than a single framework, the question of a relative sig-
niﬁcance dispute is the extent of applicability of one framework relative to
otro (Beatty 1995, pag. 66).

Beatty contends that relative signiﬁcance controversies are prevalent in
the biological sciences and can be found at all levels of biological investiga-
ción (1997, PAG. S434). De hecho, Beatty claims that “there are reasons to be
a theoretical pluralist with respect to every domain of distinctly biological
phenomena, and reasons to anticipate relative signiﬁcance controversies
within every domain” (1995, pag. 67, italics original). He argues that one
reason for this is the highly contingent nature of evolutionary outcomes10,
an aspect of evolution and biology more generally that distinguishes it from
physics where universal generalizations hold throughout a domain. To say
that evolutionary outcomes are contingent is to say that nature does not
necessitate a particular evolutionary outcome; starting with the same set
of initial conditions, evolution can result in a variety of outcomes that are
contingent upon the details of particular evolutionary histories (1995,
pag. 57). Beatty explains that evolution has produced various gene regula-
tion mechanisms, various reproductive systems, and various speciation

9. Dudley Shapere (1974) provides a detailed discussion of scientiﬁc domains, which he
describes as bodies or areas of related items that are objects of scientiﬁc investigation. Shapere
states that the 1974 paper “will not provide a systematic examination of reasons for associating
items into domains, or for associating domains into still larger domains” (pag. 526), but he is
clear that the generation of domains depends in part on the relationships between items of the
domain being well grounded and signiﬁcant (pag. 526). It is also clear from the preceding quote
and the rest of Shapere’s paper that the scope of any given domain may vary relative to another.
This is consistent with Beatty’s use of the term. Beatty’s domains are of evidentially related
phenomena that are the objects of scientiﬁc explanation.

10. Beatty (1997) is careful to distinguish what he sees as a lack of laws in biology from the
contingent nature of biology in his discussion of the reasons for the prevalence of relative sig-
niﬁcance controversies in biology. He says to attrubute the prevalence of relative signiﬁcance
issues in biology to the lack of biological laws is a restatement of the problem rather than an
explanation of it (1997, pag. S435). Beatty (1995) is clear that his thesis and argument are a
further elaboration and defense of Stephen Jay Gould’s claims about what he refers to as the
“contingent details” of evolution in Sexual Selection (1989).

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Perspectives on Science

269

mechanisms (1997, pag. S436), all of which are the contingent results of
their own distinct evolutionary histories and all of which are accounted
for by different theories and models. He acknowledges that while extreme
phylogenetic conservatism and/or extreme parallel evolution could result in
single accounts of the phenomena within biological domains, evolutionary
outcomes are more often not so constrained or conserved (1997, pag. S436).
So, Beatty concludes that “[t]o the extent that the outcomes of evolution are
not so constrained, entonces, biologists will often be faced with a variety of
alternative mechanisms, described by a variety of alternative theories or
modelos, and they will be forced to deal with issues of relative signiﬁcance”
(pag. S436). Richard Burian (1988) argues similarly that the contingent
nature of evolution suggests that a unifying synthetic theory of evolution
may not be possible despite the widespread and long-running curse of
“physics envy”, which “expresses itself in the desire for a grand unifying theory”
(pag. 257).

Where relative signiﬁcance controversies exist, there is no presumption
of the possibility of a synthetic theory like in physics. En cambio, relative
signiﬁcance controversies are indicative of a kind of theoretical pluralism11
that exists when the evidence supports the accommodation and pursuit
of more than one explanatory framework within a single scientiﬁc domain
(Beatty 1997, pag. S432). Eso es, the theoretical pluralism reﬂected by rela-
tive signiﬁcance controversies is one where a plurality of different explan-
atory theories, modelos, mechanisms, etc.. is well supported by the evidence
relevant to the different phenomena of a heterogeneous domain. Given
empirical support, different models are investigated and expanded. To ﬂesh
out what he means by theoretical pluralism, Beatty provides an example
from molecular genetics of the pursuit of more than one model of gene
regulación, such as models of negative induction, negative repression, posición-
itive induction, positive repression, and attenuation (1997, pag. S433). Allá
is a wealth of evidential support for each of the regulation models, y
molecular geneticists do not question which is the universally correct model
of gene regulation while pursuing individual models. Beatty states, “[t]aquí
is general agreement that each theory accounts for at least some instances of
gene regulation, although the issue remains as to what proportion of cases each

11. Beatty distinguishes what he means by theoretical pluralism from other kinds of theoret-
ical pluralism present in the literature in his 1995 paper, notas 22 y 23 and in the second
section of his 1997 paper. What he has in mind is different from the kind of pluralism described
by Sandra Mitchell (1992) that “refers to the incorporation of multiple, coacting causal agents
within one theory: a developmental theory that includes genetic and environmental factors, un
evolutionary theory that includes selection and drift, etc.” (Beatty 1997, pag. S433). Beatty’s
theoretical pluralism, according to him, is also different from the kind of pluralism advocated
by John Dupré (1993).

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270

Neo-Darwinism and Evo-Devo

theory correctly describes, or in other words, the relative signiﬁcance of each
theory” (1997, pag. S433 italics original).

Beatty provides several examples of relative signiﬁcance controversies
in biology, including debates over the extent of applicability of selection
theories and neutral theories to microevolutionary change, gradualist theo-
ries and punctuated equilibrium theory to macrovevolutionary change, y
a variety of theories of speciation to speciation phenomena (1997, pag. S434).
Following Beatty’s lead, other philosophers of biology have argued for other
cases of relative signiﬁcance issues. Michael Dietrich (2010), Por ejemplo,
recasts the debate over the possibility of distinct macroevolutionary causal
processes—“signiﬁcant causal processes that are found only in evolution
above the species level” (pag. 172)—as one regarding the relative signiﬁcance
of micro- and macroevolutionary processes. Through discussion of both the
emergent character approach and the emergent ﬁtness approach to thinking
about species selection, largely identiﬁed with the works of Elisabeth Vrba
(p.ej., 1984, 1989) and Elisabeth Lloyd (p.ej., 1988) and Stephen Jay Gould
(p.ej., 1993, with Lloyd) respectivamente, Dietrich argues that “[s]pecies selection
represents the best case for a distinct and unique causal process operating
only in macroevolution. Once species selection is recognized, sin embargo, el
question becomes: how frequently does it occur?" (pag. 175). He concludes
that relative to microevolutionary processes, well-established macroevolu-
tionary processes currently “are relatively rare and so are of minor evolution-
ary consequence when the entirety of the domain of evolutionary biology is
considered” (pag. 176). Dietrich explains that more cases of macroevolutionary
processes may be established in the future, and as more cases are established,
the relative signiﬁcance of such processes may increase within the hetero-
geneous domain of evolutionary biology (pag. 176). En efecto, different evolu-
tionary changes, those within populations and species and those above the
species level, can be caused, and thus accounted for, by distinctly different
kinds of processes, and Dietrich draws attention to the relative signiﬁcance
of these different kinds of processes.

Another example of a relative signiﬁcance controversy comes from Robert
Skipper (2002). Aquí, Skipper’s interest is in what he calls the “heated
debates” between Jerry A. Coyne, Nicholas Barton, and Michael Turelli
(1997, 2000) and Michael J. Wade and Charles J. Goodnight (1998,
2000) regarding Fisher’s and Wright’s evolutionary theories described in
sección 3.1 arriba. As Skipper explains, Fisher and Wright debated the de-
tails of their respective theories from 1929 until Fisher’s death in 1962, y
Wright continued to reﬁne his theory until his death in 1988 (pag. 341). El
debate led by Coyne and Wade between 1997 y 2000 “rekindled if not
thoroughly reignited the Fisher-Wright controversy,” thereby demonstrat-
ing the controversy’s persistence according to Skipper (pag. 341). Skipper

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271

conducts a detailed and thorough examination of the argumentative struc-
ture of the Coyne-Wade debate to argue that “the reignited Fisher-Wright
controversy is what Beatty (1995, 1997) calls a ‘relative signiﬁcance contro-
versy’” (pag. 342). Eso es, Skipper claims that the debate between Coyne
et al. and Wade and Goodnight is one over the relative signiﬁcance of
Fisher’s and Wright’s evolutionary theories.12 Their arguments do not
address which theory captures all evolutionary phenomena; en cambio, el nuevo
controversy acknowledges that both theories account for some phenomena
within the heterogeneous domain of evolutionary biology.

I contend that the issue of relative signiﬁcance exists for neo-Darwinian
theory and evo-devo as well. The evidence for such an issue is found within
the conﬁnes of the current debate over the relationship between the two
and the possibility of synthesis. Within this debate, there is no question
that both frameworks are well supported by the available evidence. Como un
grupo, Amundson, Minelli, Pigliucci and Müller, and Laubichler disagree
about the relationship between neo-Darwinism and evo-devo, pero ellos
agree that both are strongly evidentially supported. No one denies that
both frameworks have developed in light of decades of evidence from an
assortment of biological specialties to successfully explain and add to our
understanding of evolutionary phenomena differently conceived. This is not
to suggest that either framework is without anomalies or that the explana-
tions built using these frameworks are free of problems. Neo-Darwinism
and evo-devo are successful in part because they allow for explanations of
evolutionary phenomena that are consistent with observations, predicciones,
and explanatory frameworks from other areas of biology—like paleontology,
genomics, and cell biology, for example—and, at the same time, leave room
for fruitful remodels of and developments to their existing frameworks.

Relacionado, both explanatory frameworks are applicable within the domain
of evolutionary biology—a heterogeneous domain that includes those heri-
table changes that take place over generational and geologic time in organ-
isms and super-organisms—and again, this much is acknowledged by
Amundson, Minelli, Pigliucci and Müller, and Laubichler. Los autores
engaged in this debate agree that both frameworks explain different evolu-
tionary phenomena. As explained in sections two and three above, el

12. More particularly, Skipper argues that Coyne et al.’s conclusion that Wright’s SBT is
not explanatorily adequate is based on their assessment of the generality of scope of the SBT in
population genetics. This assessment strategy conﬂicts with how theories are to be assesed in
relative signiﬁcance controversies where explanatory adequacy is assessed based on the scope of
application and not the generality of scope. So, Coyne et al.’s assessment strategy conﬂicts with
the argumentative structure of the larger relative signiﬁcance controversy in which Coyne et al.
and Wade and Goodnight are engaged, resulting in a controversy dynamic where the partici-
pants “are, to a signiﬁcant extent, talking past each other” (pag. 342).

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272

Neo-Darwinism and Evo-Devo

debate stipulates that evo-devo explains phenomena that are left unexplained
by neo-Darwinism, speciﬁcally the evolution of phenotypes and develop-
mental entities and activities, such as Hox genes, transcription factors, y
the regulation of gene expression. Neo-Darwinism does not explain these
cosas, according to this debate, because it black-boxes the developmental
nexus that connects genes and phenotypes. This black-boxing, junto con
the different ways in which each framework conceives of genes and pheno-
types, demonstrates that neo-Darwinism and evo-devo explain different
evolutionary phenomena. And it is important to note that this debate does
not question which of these frameworks is universally applicable; this debate
does not resemble the kind of debate that is found in, decir, quantum physics
where part of what is at stake in the debate over string theory and loop
quantum gravity theory is which theory explains all of the properties of
quantum gravity, tiempo, and space. Bastante, this debate is built around the
central understanding that both neo-Darwinism and evo-devo account for
or explain some evolutionary phenomena; de lo contrario, there would be no
reason to question whether a synthesis of the two is possible.

There is the question, entonces, of which framework is more signiﬁcant, o
bastante, which accounts for the largest proportion of phenomena within the
heterogeneous domain of evolutionary biology. I take this relative signiﬁ-
cance issue to be evidence of current and future theoretical pluralism in evo-
lutionary biology. To be clear, I have in mind the same kind of theoretical
pluralism as Beatty. So, for my purposes here, theoretical pluralism, a menudo
advanced as an alternative to theoretical synthesis and reductive or elimina-
tive approaches, obtains when more than one explanatory framework is
applicable within a heterogeneous domain. A major component of Beatty’s
account of relative signiﬁcance controversies is that they are indicative of
theoretical pluralism so construed. Because of the contingency of evolution-
ary outcomes on the details of particular evolutionary histories, similar
phenomena, such as speciation events and gene regulation, are the results
of different processes that are explained by different explanatory frameworks.
En tono rimbombante, in cases where theoretical pluralism obtains, theoretical plural-
ism itself is supported by the available evidence—each theory is supported
by the available evidence, so it is not the case that theoretical pluralism
results from insufﬁcient evidence in support of a single synthetic theory
(Beatty 1997, pag. S434).

Embracing the relative signiﬁcance issue facing neo-Darwinism and evo-
devo requires acknowledging that theoretical pluralism obtains for evolu-
tionary biology. En efecto, I believe that this theoretical pluralism will continue
to be the case for some time to come. Regardless of whether a synthesis is
posible, the relative signiﬁcance issue between neo-Darwinism and evo-
devo suggests that, in light of supporting evidence, both will continue to be

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Perspectives on Science

273

pursued and further developed as individual explanatory frameworks within
this heterogeneous domain. As is the case with the relative signiﬁcance issues
discutido anteriormente, when two or more frameworks are applicable and evidentially
supported within a heterogeneous domain, those individual frameworks
continue to develop as relatively distinct frameworks. This point is particularly
clear in Beatty’s examples of reproductive systems, speciation, and gene
regulation models, as well as the example of the “persistent” Fisher/Wright
debate discussed by Skipper. As Beatty claims, a variety of models are pursued
in order to account for the heterogeneous domain of gene regulation, and these
models continue to be pursued in order to ﬂesh out the details and extent of
applicability of each. Asimismo, as illustrated by the exchange between Coyne
et al. and Wade and Goodnight, Fisher’s and Wright’s models continue to
be applied and discussed well after their developers’ deaths. At least within
biology, the kind of theoretical pluralism associated with relative signiﬁcance
issues tends to remain over time rather than give way to synthesis, reducción,
or elimination.

En efecto, I suspect that this will be the case for neo-Darwinism and evo-
devo as well. The current debate over the relationship between the two
frameworks, waged in order to answer whether a synthesis of the two ex-
planatory frameworks is possible, leads us to question their relative sig-
niﬁcance in the domain of evolutionary biology. I believe that this relative
signiﬁcance issue, Sucesivamente, indicates that both neo-Darwinism and evo-devo
will continue to be pursued and developed well into the future.

At the very least, sin embargo, I hope to have illustrated that the current
debate has missed a line of argument in favor of the possibility that theo-
retical pluralism will prevail in evolutionary biology. And it is important
to give this possibility its due consideration. As Beatty claims, generally
speaking, it is in principle possible that a theoretical synthesis may be
the resolution to relative signiﬁcance issues, but “it is by no means clear
that progress lies in the direction of a singular theory for each domain”
(1997, pag. S435). In response to David Hull’s (1987) argument that theo-
retical unity ought to be the aim of biological investigations, Beatty argues
that such an aim should be scientiﬁcally supported. If extreme phyloge-
netic conservatism and/or extreme parallel evolution are unrealistic assump-
tions in biological domains or are not supported themselves, then biologists
may not have good scientiﬁc reason to adopt a scientiﬁc methodology
that includes the stipulation that a unitary account ought to be pursued.
Beatty also brieﬂy discusses the idea that the pursuit of a single theory may
blind investigators to the heterogeneity of their domain of interest and the
idea that such pursuits may lead to oversimpliﬁcations of complex phenom-
ena and restrict new lines of research (1997, pag. S440). To avoid the possi-
bility that the question of synthesis has oversimpliﬁed the current debate or

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Neo-Darwinism and Evo-Devo

blinded it to the alternative of theoretical pluralism prevailing, I offer the
preceding argument.

5. Conclusión
en este documento, I have argued that the current debate over the possibility of a
synthesis of neo-Darwinism and evo-devo waged by Amundson, Minelli,
Pigliucci and Müller, and Laubichler misses the very real possibility that
theoretical pluralism may continue to obtain in evolutionary biology.
Through analysis of the terms and arguments of this debate, I have argued
that a relative signiﬁcance issue exists between neo-Darwinism and evo-devo,
which suggests that these frameworks will continue to develop as unsynthe-
sized individuals. Such is the case with relative signiﬁcance issues—the
theoretical pluralism that they reﬂect tends to persist in light of supporting
evidencia. Perhaps because the debate of focus is at least partially motivated
by the question of synthesis, it has failed to seriously consider theoretical
pluralism as an available alternative to future synthesis. If Beatty is correct
about the highly contingent nature of biology and its implications, y yo
believe he is, then the synthesis debate would be well served by serious
consideration of theoretical pluralism instead of synthesis.

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