## 1. Background



The notion of replication arose as a concern in the period immediately
after the Second World War (see
 Figure 1),
 with the rise of information theory, communication theory,
cybernetics, and Erwin Schrodinger's 1944 book *What is
Life?* Biologists immediately began to consider the
informational aspect of life, in each of these theoretical frameworks,
in areas ranging from neurology to molecular biology, but especially
the latter (Brookes 1956; Eigen & de Maeyer 1966; Gatlin 1972;
Johnson 1970; Linschitz 1953; Margalef 1957 [1958]; Quastler 1953;
Rashevsky 1955). It was only after the development of communications
theory by Shannon (1948) and cybernetics by Wiener (1948) after
it that inheritance in biology took on a specifically
informational tint (Griffiths & Stotz 2007). This is the case in
particular of the work of Watson and Crick on the double helix
structure of DNA (Watson & Crick 1953), as well as Crick's
Central Dogma, which states that information cannot flow from protein
to DNA. The Central Dogma (Crick 1958) was initially cast in terms of
structural information (Sustar 2007;
 Figure 2) and
 later recast by Crick as a more cybernetic or computational kind of
information (Crick 1970). [See Eugene V. Koonin 2012 & 2015 for
discussion of the nature of the Central Dogma in current biology.]



![a graph with a y axis ranging from 0% to 0.000160% and an x axis from 1800 to 2000; line stays below 0.000020% until 1960 at which point it rapidly rises to hit 0.000130% at 2000](Ngram_replication.png)

Figure 1. Yearly frequency of count for
the word "replication" in Google text's English
corpus from 1800-2000 with smoothing = 3. Data obtained from
Google Ngram Viewer (see
 Other Internet Resources).




Structural information is effectively based on the transfer of
molecular primary sequences (linear sequence) in the synthesis of
polypeptides; that is, it is the literal sequence of basic groups
(amino acids), before the protein folds into secondary and higher
conformations. This is a physical and causal account of information:
the new molecule has its sequence because it was templated in some way
by the "information"-imparting molecule (in this case, DNA
to proteins). Griffiths and Stotz (see below) call this, accordingly,
"Crick information".



However, in the late 1950s, after the structure of DNA had become more
widely understood, chemist Homer Jacobson proposed a
*cybernetic* model of reproduction (Jacobson 1958), going so
far as to make a literal model out of train sets and electronic
circuits. Later, von Neumann proposed a theory of self-reproducing
automata (Neumann 1966), which has become a parallel but influential
research program to the issue in biology (Mitchell 2009). Jacob (1973)
cemented the logical description of heredity, but the ultimate
classical source of the notion that genes are information comes from
Williams' classic 1966 book *Adaptation and Natural
Selection*, in which he referred to genes as "cybernetic
abstractions" (1966: 33).



The cybernetic notion of reproduction (and, later, replication) rested
on the notion that genes were *controllers* of phenotypes;
later, this came to be identified (e.g., by Gatlin) as synonymous with
the "communication" conception of information that Shannon
proposed. In biology, genes came to be seen as "programs"
for phenotypes [*senders*] that passed themselves on to progeny
[*receivers*], around 1961 (Peluffo 2015).



Williams' book was one inspiration for Dawkins'
*Selfish Gene* (1976), and much of what Dawkins proposed about
replicators is an extension of Williams' views, in conjunction
with those of William D. Hamilton (1964) and various ethological
ideas. This view is now known as the gene's eye view (for
discussions see Okasha 2006, Chapter 5; Agren 2021).



Williams introduced the notion of a gene as a substrate neutral
entity:



> 
> 
> I use the term 'gene' to mean that which separates and
> recombines with appreciable frequency, (1966: 20)
> 
> 
> 



and he further defined an *evolutionary* gene (that is, one
that is selectively important):



> 
> 
> [A] gene could be defined as any hereditary information for which
> there is a favorable or unfavorable selection bias equal to several or
> many times its rate of endogenous change. (1966: 25)
> 
> 
> 



His answer to the question of what a gene is, is that a gene is
evolutionary just insofar as it is something heritable that is subject
to rates of selection that exceed the mutation rate. This is a
definition, not a discovery. If it is favorably or unfavorably
selected and heritable, it is an evolutionary gene. According to this
definition, items that are not made of DNA can be classed as
evolutionary genes so long as they match Williams' definition
(Lu & Bourrat 2018).



![a rectangle divided into three horizontal regions, the first region has a purple background and is titled 'Replication' and has a diagram with the word 'DNA' and an arrow going from 'DNA' and circling back to it; the second region has a yellow background and is titled 'Transcription' and the diagram continues with an arrow from 'DNA' in the previous region to the word 'RNA' in this region; the third region has a green background and is titled 'Translation' and the diagram continues with an arrow from 'RNA' in the previous region going into this region and ending.](centraldogma.png)

Figure 2. The Central Dogma of genetics
as envisaged by Crick around 1965 (Thieffry & Sarkar 1998).



## 2. Genes and Information



The language of "codes" and "information"
flows easily enough with respect to replication [see the entry
 biological information].
 Transcription, translation, punctuation, redundancy, synonymy,
editing, proofreading, errors, repairing of errors, messages, copies,
and information all sound natural enough. Yet, the literature dealing
with information is both extensive and factious. Several different
formal analyses of information can be found and very little agreement
about which analysis is best for which subjects. On one point, these
scholars tend to agree--cybernetic information and
communication-theoretic information will not do for replication in
biological contexts. Some argue for semantic information
(Godfrey-Smith 2000a; Sarkar 2000; Sterelny 2000b). The trouble is
that no widely accepted version of semantic information exists. Winnie
(2000) distinguishes between Classical and Algorithmic Information
Theory and opts for a revised version of the Algorithmic Theory. But,
once again, the problem is that no such formal analysis currently
exists.



In the face of all this disagreement and unfinished business,
biologists such as Maynard Smith (2000) maintain either that informal
analyses of "information" are good enough or that some
future formal version of information theory will justify the sorts of
inferences that they make. The sense of "information" used
in the Central Dogma of molecular biology is more like a fit of
template, or the primary structure of the protein sequence compared to
the sequence of the DNA base pairs. Attempts have been made in what is
now known as bioinformatics to use Classical Information Theory
(Shannon's theory of communication) to extract functional and
phylogenetic information (Brooks & Wiley 1988; Gatlin 1972;
Maclaurin 1998; Rodrick Wallace & Wallace 1998), but they appear
to have been unsuccessful in the main.



While the most likely conclusion is that no version of information
theory as currently formulated can handle "information" as
it functions in biology (Griffiths 2001), attempts have continued to
be made to formulate just such a version (Bergstrom & Rosvall
2011; Sternberg 2008). However, this undercuts the motivation for
appealing to information theory to elucidate genes in the first
instance. Griffiths & Stotz (2013: 153) have argued for
"Crick" information, which they define as "the
specification of the order of amino acids in a polypeptide
chain". This specificity definition is more chemical than
abstract [see the section below on
 Developmental Systems Theory].



The "informational gene" conception, as James R. Griesemer
(2005) terms it, is a highly abstract concept of a process and the
entities that comprise it. This is intentional, as it permits
Darwinian dynamics to be applied to a range of phenomena, such as
sociocultural, cybernetic, and medical processes. However, this raises
a metaphysical concern, namely that the view that a gene is nothing
but information is a version of Aristotelian hylomorphism [see the
entry
 form versus matter].
 That is, information is a type of form, which can be used to explain
physical processes. Classical hylomorphism was roundly demolished as a
*scientific* hypothesis when Daltonian elements were named and
investigated in the nineteenth century. By 1900, terms like
"substance" (for matter that is propertyless apart from
mass and extension in space) and "form" had taken on a
largely philosophical sense that differed extensively from
Aristotle's own physical views. Griesemer notes:



> 
> 
> We know that the informational genes are tied to matter and structure,
> but if evolutionary theory - to be general enough to cover
> cultural and conceptual change - must be devoid of all reference
> to concrete mechanism, it cannot follow from the theory, for example,
> that genes are inside organisms or are even parts of organisms, as
> Dawkins's language suggests. Strictly, only the correlations
> between replicator and vehicle due to causal connections of a
> completely unspecified sort can be implied by such a theory. Striving
> to get matter and specific structure out of the theory in order to
> make it apply to immaterial realms may thus leave it bankrupt as an
> account of causal connection for the material, biological cases.
> (2005: 79)
> 
> 
> 



And yet, this kind of hylomorphism has remained, even in science.
Biologists have argued that form determined many properties of
organisms in ways that could not be reduced to the actions of their
parts, and this kind of thinking remained and was co-opted by the
molecular biologists and geneticists. Thus, we get the Central Dogma
of molecular biology:



> 
> 
> The Central Dogma
>   
> 
> This states that once 'information' has passed into
> protein *it cannot get out again*. In more detail, the transfer
> of information from nucleic acid to nucleic acid, or from nucleic acid
> to protein may be possible, but transfer from protein to protein, or
> from protein to nucleic acid is impossible. Information means here the
> *precise* determination of sequence, either of bases in the
> nucleic acid or of amino acid residues in the protein. (Crick
> 1958)
> 
> 
> 



Read physically, this means only that the structure of the DNA
molecule is not reproduced from the structure of proteins, a perfectly
reasonable account of the molecular processes. However, because Crick
used the word "information", some scientists, including
Dawkins, took this to mean that genes are informational entities,
which "code" for organismic traits from the molecular
level up to the entire organism and even beyond. This is striking in a
purple passage of *The Blind Watchmaker*, where Dawkins
describes genes as follows:



> 
> 
> It is raining DNA outside. [downy seeds from willow trees] ...
> The cotton wool is mostly made of cellulose, and it dwarfs the tiny
> capsule that contains the DNA, the genetic information. The DNA
> content must be a small proportion of the total, so why did I say that
> it was raining DNA rather than cellulose? The answer is that it is the
> DNA that matters... whose coded characters spell out specific
> instructions for building willow trees... It is raining
> instructions out there, it's raining programs; it's
> raining tree-growing, fluff spreading, algorithms. That is not a
> metaphor, it is the plain truth. It couldn't be any plainer if
> it were raining floppy disks. (1986: 111)
> 
> 
> 



So, we now turn to Dawkins' view of genes as
replicators and the way in which he takes information to be
cybernetic and physical at the same time.


## 3. Dawkins' View



Richard Dawkins introduced the distinction between replicators and
vehicles in *The Selfish Gene* (1976). For his purposes,
Dawkins found the contrast between genes and organisms too restrictive
and specific. Everyone agrees that genes are replicators, but genes
may not be the only replicators. Dawkins also argued that perhaps more
inclusive entities than single genes might also function as
replicators. At the very least, the possibility should not be ignored.
So, Dawkins adopted "replicator" as a more inclusive and
general term than "gene". In *The Extended
Phenotype*, he defined a replicator as "anything in the
universe of which copies are made" (Dawkins 1982b: 83). He also
introduced the term "vehicle" for those entities produced
by replicators that help these replicators increase in numbers by
interacting effectively with their environments. This distinction can
be expressed in terms of either entities or processes. According to
Dawkins, replicators function in replication, while vehicles function
in environmental interaction.


### 3.1 Genes as Replicators



A longstanding dispute in evolutionary biology concerns the levels at
which selection can occur (Bourrat 2015b, 2021; Brandon 1996;
Kerr & Godfrey-Smith 2002; Keller 1999; Lloyd 1988; Okasha 2006,
2016; Sober & Wilson 1998; Williams 1966) [see the entry on
 units and levels of selection].
 Some authors see this dispute as concerning the levels at which
replication can take place. Other authors take the levels of selection
dispute to concern environmental interaction and insist that
environmental interaction can take place at a variety of levels, from
single genes, cells, and organisms to colonies, demes, and possibly
entire species. Organisms certainly interact with their environments
in ways that bias the transmission of their genes, but then so do
entities that are both less inclusive than entire organisms (e.g.,
sperm cells) and more inclusive (e.g., beehives).



Dawkins argued that replication in *biological* evolution
occurs exclusively at the level of the genetic material. The term
"replication" refers first and foremost to copying, and
genes are the self-replicating molecules of biology. Some critics
(e.g., Lewontin 1991: 48) interpreted this to mean that a strand of
DNA placed on a glass slide might start replicating all on its own. Of
course, no biologist has ever held such a view. Genes do replicate
themselves, but only with the aid of highly complicated molecular
machinery. Too often, however, the importance of this machinery has
gone unnoticed. To be sure, when we make copies on a photocopier, we
are interested in the texts, figures, or just scrawls that appear on
these sheets of paper. We are not interested in how the photocopier
works, even if it does *all* the work.



In Dawkins' early writings, replicators and vehicles played
different but complementary and equally important roles in selection;
however, as he honed his view of the evolutionary process, vehicles
became less and less fundamental. Initially, Dawkins was content to
dethrone the organism from its pride of place in biology. It is an
important focus of environmental interaction, but other entities, both
below and above the organismic level, can also function as vehicles.
In later writings, however, Dawkins went even further to argue that
phenotypic traits are what really matter for evolution by natural
selection to occur and that they can be treated independently of their
being organized into vehicles. More than that, features such as spider
webs should be viewed as part of a spider's phenotype. Hence,
Dawkins titled his second book *The Extended Phenotype*
(Dawkins 1982b).



Dawkins never lost his fascination with vehicular adaptations, a
fascination that his critics denigrate as Panglossian adaptationism.
He filled his books with adaptationist scenarios, some more firmly
supported by data than others; however, from the perspective of
the structure of evolutionary theory, he held that replicators are
much more important than vehicles. For example, Dawkins argued at some
length that adaptations are always for the good of replicators, not
vehicles (Lloyd 1992) [see the entry on
 units and levels of selection].
 Vehicles *exhibit* these adaptations, but ultimately all
adaptations must be *explicable* in terms of changes in gene
frequencies. Thus, it comes as no surprise when Dawkins (1994: 617)
proclaims that he "coined the term 'vehicle' not to
praise it but to bury it". As prevalent as organisms might be,
as definite as the causal roles that they play in selection are,
reference to them can and must be omitted from any perspicuous
characterization of selection in the evolutionary process. Although
Dawkins is far from a genetic *determinist*, he is certainly a
genetic *reductionist*. Whether reductionism itself is good or
bad is a moot question (Sarkar 1998).



According to Dawkins, replicators have three basic
properties--*longevity*, *fecundity* and
*copy-fidelity*. Longevity means longevity of the gene
*type* in the form of copies through descent (Dawkins 1982b:
84; Hull 1980), although the stability of gene *tokens* is
included in the definition in *The Selfish Gene* (1976: 18). No
gene as a physical body lasts all that long. In mitosis, a gene loses
half of its substance at each replication. What endures, he says, is
not the entity itself but the information incorporated in its
structure. It is this information that is copied with such high
fidelity. Mutations do occur, but at very low frequencies. Even so, in
some organisms, mutation rates must be too high because mechanisms
have evolved that search out and repair such errors. Therefore, the
genotype is an informational notion; information is equivalent to
Aristotelian form. The type is the *form* of the tokens, in
Dawkins' view.



One source of variation in genes of sexual organisms supplementing
mutation is crossover. Pairs of homologous chromosomes line up next to
each other at meiosis, crossover, and recombine. For stretches of DNA
in which different alleles exist, the result can be a change in
information. Quite obviously, the shorter the stretch of DNA involved,
the less likely that crossover will occur and the message change.
Dawkins appeals to such dismantling of entities to argue against
organisms functioning as replicators. In sexual organisms, organisms
themselves are torn apart and repeatedly assembled each generation
(Caporael 2003). If long stretches of DNA lack the necessary identity
by descent to function as replicators, then sexual organisms certainly
lack it. However, some other explanation has to be provided for
asexual organisms because they pass on their overall structure largely
unchanged from generation to generation. For example, R. A. Fisher,
in *The Genetical Theory of Natural Selection* (Fisher
1930) considered the entire genetic complement of asexual organisms to
be a single gene, and this view has been repeated from time to time
since. According to Dawkins, genes, and only genes, can function as
replicators in biological evolution. How large these genetic units are
depends on such things as the prevalence of sex, the frequency of
crossover or lateral gene transfers, and the intensity of
selection.



> 
> 
> If there were sex but no crossing-over, each chromosome would be a
> replicator, and we should speak of adaptations as being for the good
> of the chromosome. If there is no sex we can, by the same token, treat
> the entire genome of an asexual organism as a replicator. But the
> organism itself is not a replicator. (Dawkins 1982a: 95)
> 
> 
> 



Dawkins offered two reasons for organisms not being able to function
as replicators. The first is the one he uses to delineate evolutionary
genes. As is the case for long stretches of DNA, organisms are too
easily and frequently broken up to be considered units of replication.
A second reason is that they cannot pass on changes in their
structure, although some phenotypic change may result in generational
change. In fact, *some* epigenetic mechanisms have been shown
to be passed on across generations (Jablonka & Raz 2009; see the
entry on
 inheritance systems).
 The amount of DNA that counts as a replicator certainly varies; but,
according to Dawkins, nothing more inclusive than the genetic material
functions as replicators in biological evolution.



In *The Selfish Gene*, although Dawkins wanted his definition
of gene to be close to that of Williams' (1966)
"evolutionary gene", it is not quite:



> 
> 
> A gene is defined as any portion of chromosomal material which
> potentially lasts for enough generations to serve as a unit of natural
> selection. (Dawkins 1976: 30)
> 
> 
> 



Where Williams' definition is substrate neutral, Dawkins'
is explicitly chromosomal and DNA-based. Where William's
"gene" refers to *any* entity, which is the reason
why it is an informational notion, Dawkins' gene, by contrast,
is tied to DNA, a view later heavily criticized by Stent (1977),
an influential molecular biologist at the time.



On Dawkins' account, the limits of genes need not be absolutely
sharp. Nor must all genes be of the same length. The greater the
selection pressure, the smaller the gene. At the most fundamental
level, selection takes place between alternative alleles residing at
the same locus.



> 
> 
> As far as a gene is concerned, its alleles are its deadly rivals, but
> other genes are just a part of its environment, comparable to
> temperature, food, and predators, or companions. (Dawkins 1976:
> 40)
> 
> 
> 



Alleles cannot cooperate with each other, only compete. That is
where the "selfish" in "selfish gene" comes
in. According to Dawkins (1976: 95), the selfish gene is not just one
physical bit of DNA. It is "all replicas of a particular bit of
DNA, distributed throughout the world" (for a recent defense of
a similar approach, see Haig 2012). Hence, genes do not form classes
of spatiotemporally unrelated individuals but trees. They must be
replicas. But, being a replica is not enough. The linear repetition of
the "same gene" in the form of several hundred copies is
quite common. These replicas, however, do not reside at the same
*locus*. Although identical in structure, these genes do not
compete with each other in the way that alleles at the same locus can.
In the simplest and most basic sense, alleles compete with alternative
alleles at the same locus. Any other sorts of competition and
cooperation are merely extrapolations from this fundamental sense of
allelic competition. Although genes may cooperate with each other in
very complicated ways in embryological development, in replication
they can be treated as "separate and distinct". In
development, the effects of genes blend. In replication, replicators
do not blend.


### 3.2 Hull's Interactors



Dawkins introduced the general notions of replicator and vehicle so
that selection need not be limited exclusively to gene-based
biological evolution. However, as the preceding discussion indicates,
his later revisions to his general theoretical outlook were influenced
strongly by the traditional perspective of genes and organisms. Genes
contain the information necessary to produce organisms and their
adaptations. Genes "ride around" in and
"guide" organisms. As Dawkins describes them, vehicles are
relatively discrete entities that "house" replicators and
that can be regarded as machines programmed to preserve and propagate
the replicators that ride inside them. Although these terms may be
appropriate for the relations between genes and organisms, they
interfere with a more general analysis of replication and selection.
What really matters in selection is that entities at various levels of
organization interact with their environments in such a way that the
relevant replicators increase in relative frequency. The actual causal
chain that connects replicators and vehicles need not be limited to
development.



For example, Dawkins argues at some length that genes and only genes
can function as replicators in biological evolution. He adds that
"all adaptations are for the preservation of DNA; DNA itself
just is" (Dawkins 1982a: 45). But, DNA itself exhibits
adaptations. Anyone who has spent much time examining the molecular
structure of DNA soon realizes that it is adapted to replicate. In
addition, the proliferation of junk DNA, transposons, and meiotic
drive are three examples in which the only phenotypes that matter are
phenotypic characteristics of genes (Brandon 1996; Sterelny 1996:
388). Dawkins' characterizations of replicators, vehicles, and
the relations between the two are too closely tied to genes,
organisms, and development. DNA can certainly replicate itself, but it
can also function as a "vehicle", even though it cannot
code for, ride around in, or direct itself. In sum, a more general
characterization of selection is needed, a characterization that does
not assume that the only causal connection between replicators and
vehicles is development from embryo to maturity. Such a generalization
was offered by Hull (1980, 1981, 1988), who proposed that the relevant
notion is "interactor" rather than "vehicle",
as interactors are causal and active while vehicles are passive
entities.


## 4. Other Examples of Replicators



Although Dawkins finds it desirable to replace genes with replicators
in his general characterization of the evolutionary process, he says
very little about this more general notion in *The Selfish
Gene*. Only one chapter (11) is dedicated to "memetic"
evolution. Instead, as we saw, he discusses the special case of genes
as replicators. The primacy of the genetic perspective in the
characterization of replicators is claimed by some (Griesemer 2000b)
to be one of the chief weaknesses not only in Dawkins'
discussions but also in the work of his successors [see the section
below on
 Reproducers].
 Hull and his colleagues (Hull, Langman, & Glenn 2001) claim to be
providing a general notion of replication, adequate to handle all
different sorts of replication, when too often we are simply reading
peculiarities of genetic replication into our general analysis of
replication.


### 4.1 The Immune System



Does replication play the same role in other sorts of selection that
it plays in gene-based biological evolution? The reaction of the
immune system to antigens is closest to the standard biological
example of replication and selection (Hull et al. 2001). Certainly,
immune systems arose through the same process as other functional
systems. The basic structure of the human immune system is
"built into our genes", and the only genes that count in
evolution are the ones that we received from our ancestors and can
subsequently pass on to our progeny. In Dawkins' (1982b: 83)
terminology, the genes that code for our immune system are active,
germ-line replicators. They are active because they influence their
probability to be copied; they are germ-line because they can
potentially have an infinity of descendants.



However, the genes that function in the reaction of the immune system
to antigens have two peculiarities. First, they incorporate mechanisms
designed to produce very high frequencies of mutation; second, none of
the genes involved in the functioning of the immune system are
germ-line. For instance, the genes that give rise to B-cells are
designed to mutate extensively until one of these cells identifies an
invader as foreign. It then proliferates extensively as it attacks the
invader. As an organism matures, it accumulates more and more of the
B-cells that have been successful in its past. More than this, as
the process of proliferation continues, the strength of the affinities
to binding sites increases. Initially, the primary antibodies almost
always exhibit a weak affinity for their targets; however, as the
reaction to the antigen continues, these affinities become
stronger.



Within the confines of a single organism, the reaction of the immune
system to antigens has all the characteristics of selection processes;
however, when the organism dies, all of these adaptations are lost. In
some species, females pass on not only the genes for the basic
structure of their immune systems but also some of the machinery that
past invasions of antigens have produced in them. However, these cells
are rapidly removed from the offspring as it develops its own immune
system. The reaction of the immune system to antigens departs from
gene-based selection in biological evolution in two ways. First, from
the organismal perspective, the genes that function in protecting an
organism from invaders are not germ-line. They are somatic. Second,
the relevant mutation rates are much, much higher in the immune system
than in ordinary gene-based selection. Instead of mechanisms existing
to discover mutations and repair them, mechanisms exist that encourage
mutations--massively so. If the functioning of the immune system
is to count as an adaptive process, some changes must be made.
One possibility is to clarify what counts as a "germ-line"
replicator and reject the notion that extremely low mutation
rates are inherent in all selection processes [see the section below
on
 Challenges to the Replicator].


### 4.2 Sociocultural Evolution



The temptation to regard cultures and societies as evolving entities
in a way analogous to organisms has a long tradition. In *The
Selfish Gene* (Chapter 11), Dawkins proposes a version of it that
makes use of the concept of the replicator. He chose the word
"meme" for a sociocultural replicator due to its
similarities with the word gene:



> 
> 
> We need a name for the new replicator, a noun that conveys the idea of
> a unit of cultural transmission, or a unit of imitation.
> 'Mimeme' comes from a suitable Greek root, but I want a
> monosyllable that sounds a bit like 'gene' (Dawkins 1976:
> 192).
> 
> 
> 



The basic idea underlying Dawkins' proposal is that since
evolution by natural selection in the biological domain requires
replication, it must also be the case in the sociocultural domain, and
that imitation, at least in many cases, is the way through which
sociocultural entities, the memes, replicate.



Important differences exist between sociocultural evolution and
biological evolution (Claidiere & Andre 2012) [see
the entry on
 cultural evolution].
 For example, Dawkins (1976) admits that he is on shaky ground when it
comes to the high-fidelity copying required of replicators. Memes seem
to get changed much more frequently than genes (see Sterelny (2006)
for a review). In general, however, it is fair to say that the
standards used to evaluate sociocultural transmission are not on par
with those used to evaluate biological transmission. An overly
idealized view of Mendelian genetics is contrasted with a much more
realistic view of cultural change. So the criticism goes, one problem
with memes is that they do not have discrete boundaries, do not all
come in the same size, and, in their functioning, are strongly
influenced by their environments. Genes, so the critics claim, have
sharp boundaries, are all of the same size, and are immune to
environmental influences. If sociocultural evolution is to be
evaluated fairly, the same level of criticism must be applied to all
putative examples of selection, from gene-based selection in
biological evolution and the reaction of the immune system to antigens
to the development of the central nervous system and social learning
(Hull et al. 2001). The collection of articles in Aunger (2000)
present the arguments for and against a memetic approach to
culture, and a more recent discussion is available in Lewens
(2015).



Dawkins (1976) also places considerable emphasis on human brains as
the "vehicles" for memetic evolution. He defines
"meme" as an entity capable of being transmitted from one
brain to another. Computers are also plausible vehicles for memes, as
well as artifacts more generally, which can "store" and
then release information when a copy of the artifact is made by
emulation (*mimesis*): that is, without the presence of a
demonstration. However, Dawkins' discussion of memes
is marred by the pervasiveness of the gene-organism perspective.
For example, he defines "replicator" in terms of
transmission of information--memes leaping from brain to brain or
from brains to computers and back again. But, memes do not leap from
brain to brain or from computer to computer. Their content is
transmitted in a variety of ways, including books, audiotapes,
conversations, and the like. As much as the physical basis changes,
the message remains sufficiently unchanged. All instances of this
message are equally memes, not just the ones residing in human brains
and computers.



Several accounts of memetic replication have been proposed in the
literature. Some consider that there is no replication in cultural
evolution, but that memes are "attractor points" in
culture (Atran 1998). Others consider that the interactor is the meme
itself (Blackmore 1999) or that the meme is the selected cultural
heritable information, just as Williams' "evolutionary
gene" is the selected genetic heritable information, and the
memetic interactor is the repertoire of behaviors it elicits (Wilkins
1998). One view that has been offered several times is that memes are
active neural structures (Aunger 1998, 2002; Delius 1991).



All the objections to the gene-meme analogy to one side, Dawkins
(1976: 211) finds the chief difference between genetic and memetic
change is that biological evolution is at bottom a war between alleles
residing at the same locus: "Memes seem to have nothing
equivalent to chromosomes and nothing equivalent to alleles".
First, the usual depiction of alleles residing at the same locus on
homologous chromosomes so central to Mendelian genetics is an
oversimplification; but, and more importantly, for at least half of
the history of life on earth, replication and selection took place in
the absence of chromosomes, meiosis, and the like. If gene-based
biological evolution took place for so long in the absence of the
Mendelian apparatus and still does so in many extant organisms, then
demanding that memetic evolution proceeds by this very special and
possibly aberrant sort of inheritance seems too strong. The cost of
meiosis remains a serious problem in ordinary biological evolution.
Demanding that cultural evolution incorporates this same highly
problematic element in its own makeup seems strange in the extreme. If
we are to develop a general analysis of selection, we must
distinguish between essential and contingent features of this
process.



Numerous evolutionary biologists question how fundamental to selection
the perspective of alleles at a locus actually is. Almost everyone
agrees that evolution involves changes in gene frequencies. However,
few go on to add that evolution is *nothing but* changes in
gene frequencies. When one looks at evolutionary biology, one
discovers that it involves much more than changes in gene frequencies.
To be successful, memetic evolution must be fleshed out.



In 2000, Aunger summarized the disputes between proponents and
skeptics of the memetic approach as revolving around three
levels:



> 
> 1. whether culture is properly seen as composed of independently
> transmitted information units;
> 2. whether these so-called memes have the necessary qualifications to
> serve as replicators; and
> 3. whether a Darwinian or selectionist approach such as memetics is
> the most feasible or desirable form for a science of culture to take.
> (Aunger 2000: 11)
> 
> 
> 



However, over 20 years after the diagnosis, it seems that the
memetic approach has, by and large, been abandoned, with some of its
insights incorporated into other evolutionary approaches to culture.
Perhaps the most successful is dual-inheritance theory (Richerson
& Boyd 2008), also known as gene-culture coevolution. A very
general characterization of sociocultural evolution has been attempted
by El Mouden, Andre, Morin, and Nettle (2014). This approach,
which relies on the most abstract formalism used by evolutionary
theorists--namely, the Price equation (for an introduction to the
Price equation see Okasha 2006: Chapter 1)--highlights some
of the differences between biological and sociocultural evolution, and
why a pure memetic approach seems difficult to implement as a general
framework.


### 4.3 The Extended Replicator



Some of Dawkins' critics think that genes play too important a
role in his notion of replication. Replication, so they argue, can
occur at other levels of organization as well. Just as Dawkins
extended the notion of the phenotype, these authors propose to make
the notion of replicators more general as well--to extend the
replicator so to speak. Dawkins introduced his *Extended
Phenotype* conception for two reasons. First, he wanted to extend
the notion of a "phenotypic trait". The sort of nest that
a bird builds or the song that it sings can count as phenotypic traits
just as much as the shape of its bill. Second, as mentioned earlier,
Dawkins wanted to break the hold that organisms have over how we
conceptualize the living world. Traits do tend to come bundled into
reasonably discrete entities; but, for making inferences about the
evolutionary process, traits can be treated as separate and distinct.
However, as he proceeded, Dawkins eventually decided that extending
the phenotype was not enough. He had to bury it. All sorts of
fascinating mechanisms to one side, what really matters in selection
takes place at the level of replicators.



Although such critics of Dawkins as Sterelny, Smith, and Dickison
(1996) declined to join with Dawkins in his demotion of environmental
interaction, they did agree with him that replicators are special.
They play a special role in development. However, they do not limit
replicators to genes, even in biological evolution. Sterelny et al.
propose to extend the replicator to include nonstandard entities:
"the set of developmental resources that are adapted from the
transmission of similarity across the generations" (Sterelny
2001: 338). For example, the sort of burrow that a particular organism
digs is influenced by its genetic makeup; however, if these burrows
are used over and over again, characteristics of these burrows can
themselves be viewed as replicators. The effects of these burrows get
passed on from generation to generation, but not via the DNA.



As more and more non-DNA replicators, including epigenetic
inheritance, are acknowledged, Dawkins' view began to grade into
the conception of the Extended Replicator, which Sterelny et al.
(1996) specify as any non-genetic as well as genetic replicators where
"genetic" refers to DNA. These two views are so
general that any case that can be described in one can be redescribed
in the other. Differences lie in ease of description. According to
Sterelny et al. (1996), the burrows that some organisms dig can
function as replicators--extended replicators--while Dawkins
portrays them as instances of extended phenotypes. The contrast is
between selfish burrows and selfish genes for burrowing.



In the version of replication formulated by Sterelny et al. (1996),
both copying and biofunction are crucial. Copying is quite obviously a
causal phenomenon, but not any old causal connection will do.
Similarity of copies is necessary but not sufficient. These
copies must be copies of copies. One copy must produce another copy
and that copy produce still another copy and so on. For one entity to
be a copy of another, it must be the output of a process whose
biofunction is to conserve function. The function of copying is to
produce from one token another token, which is similar in the relevant
respects. Genes fit this definition, but so do lots of examples of
non-genetic transmission, such as habitat stability resulting from
nest site imprinting, the song that a bird learns, and various
microorganism symbionts, not to mention sociocultural
transmission.


## 5. Challenges to the Replicator


### 5.1 Developmental Systems Theory



In the wake of Oyama's *The Ontogeny of Information*
(1985, 2000) and other work, notably that of Daniel Lehrman (1953) and
Patrick Bateson (2001), a view of biological evolution has arisen that
emphasizes development (see also Griffiths & Gray 1994a). In the
nineteenth century, development was an extremely active research
program. The next great discoveries in biology were predicted to be in
the area of development; however, this was not to be. First
Mendelian genetics and then a version of evolutionary theory centered
on population genetics took over biology, and they did so while
avoiding development. Everyone knew that development was central to
both evolution and reproduction, but no one could see how to integrate
the masses of developmental data available into the emerging synthesis
of evolutionary biology and genetics. As a result, development was
left out of the Modern Synthesis (Beurton, Falk, & Rheinberger
2000; Gilbert 1991). Considering how central development actually is
in metazoan and metaphyte biology, the advances made while ignoring it
are staggering.



Even so, developmental biology continued on its course until, at long
last, we seem to understand development well enough to begin
integrating it into the rest of biology. On the most conservative
view, current versions of evolutionary theory can remain largely
unchanged as development is grafted onto them. On a second view, both
perspectives are likely to require some modification to achieve this
integration. Our understanding of development may have to be modified,
but so too for evolutionary theory (Pigliucci & Muller 2010).
Finally, at the other extreme, development will all but replace
evolutionary theory. In their more exuberant moments, some advocates
of Developmental Systems Theory (DST) seem to be claiming just that.
Just as some molecular biologists think that molecular biology is
rapidly replacing all the rest of biology, some advocates of DST argue
that developmental theories will simply replace current versions of
evolutionary theory.



On some versions of the DST view, genes have no uniquely privileged
role in repeated cycles of development (Griffiths 2001; Griffiths
& Gray 1994b). In fact, no element of the developmental matrix
plays any privileged causal role--not genes, not organisms, not
the environment, not anything. Everything counts as a resource;
however, in particular situations, certain resources will play
more important roles than other resources. In rejecting any privileged
role for genes, advocates of DST are especially skeptical of one
particular role supposedly played by genes--the transmission of
information. According to some, information is central to
developmentalism, but genes are not the only mechanisms for
information transfer. According to others, information plays no role
in the emerging developmentalist perspective. The developmental system
as a whole is the unit of selection [see the entry on
 units and levels of selection].
 If genes have no special role and whole developmental cycles are
replicators, as some developmental systems theorists argue, the
distinction between replicator and interactor becomes blurred.



In the continuing debate over developmental versus traditional
theories of evolutionary biology, Sterelny et al. (1996) hold a fairly
conservative position. They agree with the developmentalists that
genes play no privileged role in the development of phenotypes from
genotypes. Genes do play a role in this process, simply not a
*privileged* role. Genes can serve as a causal bridge from
phenotype to phenotype, but other entities can do so as well. Genes
are not the only replicators in biological evolution. The repeated
cycles in inheritance include many different sorts of constancies and
repetitions--genes, cellular machinery, phenotypic traits
including behaviors, and social structures. Information remains
central to selection processes, but genes are not the only carriers of
such information. Genes predict phenotypic characters only in the same
sense that environmental factors predict them. Sterelny (2000a) has
argued that developmental considerations require no fundamental
reevaluation of evolutionary conceptions along the lines of DST.


### 5.2 Evolution by Natural Selection without Replication



Godfrey-Smith (2009; see also Godfrey-Smith 2000b; Griesemer 2005)
contrasts the replicator/interactor approach to natural selection with
a more classical approach. This latter approach is usually given as a
"recipe" for evolution by natural selection, to use
Godfrey-Smith's terminology (see also Brandon 1990: 3.1). Ever
since Darwin, a number of authors have proposed that for evolution by
natural selection to occur, three conditions or ingredients are
necessary. A population should exhibit (1) variation that (2)
leads to differences in fitness between the entities forming the
population [see the entry on
 fitness],
 (3) which are heritable (reviewed in Godfrey-Smith 2007). The most
famous version of these recipes is that provided by Lewontin
(1970).



There is a difference in emphasis between the two approaches in that
the replicator/interactor approach focuses on the *entities*
forming the population, while the classical approach provides a
population description of evolutionary change. Another difference
between the two approaches is that under the classical approach,
replication is not required for evolution by natural selection to
occur. In fact, as long as heritability is positive, and the two other
conditions are satisfied, evolution by natural selection can occur
(but will not necessarily do so, cf. Godfrey-Smith 2009: 25). An
abstract definition of heritability (\(h^2\))--although by no
means fully general (see Bourrat 2015a, 2022)--is that it
represents the slope of the regression of average offspring character
on parent or mid-parent (in case of sexual species) character [see the
entry on
 heritability].
 Given that a positive heritability does not entail replication of
character between parent and offspring, but is rather a special
case in which heritability would be exactly 1 in the absence of
environmental variation, the replicator/interactor perspective is
subsumed by the classical approach. Godfrey-Smith concurs:



> 
> 
> From this point of view, we can see the replicator analysis as picking
> out a special case of what is covered (or supposed to be covered) by
> the classical view. (2009: 36; see also Godfrey-Smith 2000b)
> 
> 
> 



To see why a lack of replication does not prevent evolution by natural
selection from occurring, suppose a population of entities exists with
different sizes, as presented in
 Figure 3(a),
 in which there is selection for larger entities. We assume that the
entities reproduce asexually in discrete generations and that there is
no environmental variation. At the parental generation, there are two
types of individuals, with respective sizes of \(\frac{3}{4}\) and 1.
Due to the selection for size, entities of size \(\frac{3}{4}\)
produce 3 offspring while entities of size 1 produce 4 offspring.
Suppose now that there is a positive heritability, as defined above,
so that, on average, offspring resemble more their parent than they
resemble other entities of the parental generation, as displayed on
 Figure 3(a),
 but only slightly so (\(h^2 = 0.2\)). After one generation, although
there is no high-fidelity replication, the average size of the
population has changed due to the effect of natural selection.
This simple example demonstrates quite straightforwardly that
replication is not required for evolution by natural selection to
occur.



We said earlier that replication would imply a heritability of exactly
1 in the absence of environmental variation. Although this is correct,
the reverse is not true. In fact, take again a similar population as
in
 Figure 3(a),
 but this time assume a different pattern of inheritance for the two
types of entities, as displayed in
 Figure 3(b).
 With this pattern of inheritance, although there is no replication,
entities *on average* have the exact same character
value as their parent. In the case of the entities of size
\(\frac{3}{4}\), *some* offspring have the exact same character
as their parent, but that is not required either, as is the case with
the entities of size 1, of which none of the offspring has the same
character as their parent.



One possible response against regarding the classical approach to
evolution by natural selection as unconditionally superior to the
replicator/interactor approach is to argue that although
evolution by natural selection can occur without replication, when
this happens, the evolutionary change resulting is not a *pure*
case of evolution by natural selection. Rather, it is evolution by
natural selection mixed with some other evolutionary processes. A
rationale for this claim is that the fact that offspring do not
resemble their parent introduces some variation into the population of
which the origin is not natural selection. In abstract terms, the
introduction of variation can be regarded as a form of mutation
(Bourrat 2019). Under this interpretation, the classical
approach, on the one hand, and the replicator/interactor approach, on
the other hand, simply emphasize different aspects of evolutionary
explanations. The classical approach gives us evolutionary
explanations *in the context of other evolutionary processes
occurring*, while the replicator/interactor approach gives us
evolutionary explanations *of what the effect of natural selection
would be in the absence of any other evolutionary process acting in
the population*--that is, in its pure form. Understood that
way, the two approaches do not necessarily need to be opposed.



Another problem with the idea of replication is that it is description
dependent. Described finely, two objects can never be identical. The
same applies to parents and offspring. This, in itself, does not
represent a challenge to the replicator/interactor view. However,
and more problematically, a coarser grain of description might
lead parents and offspring to be regarded as copies of one another
when a finer-grained description would show that they are not. Such a
coarse-grained way of viewing evolutionary processes has been endorsed
by some memeticists (see Boudry 2018; Dennett 2017 for explicit
defences). However, without a principled way to choose which
grain(s) of description ought to be used for the study of a particular
evolutionary setting, the claim that replication is fundamental to
evolution by natural selection in the context of other evolutionary
processes occurring becomes arbitrary. This problem is a general one
in evolutionary theory (see Bourrat, 2020), but is even more
problematic in the context of cultural evolution where the
line between genotype and phenotype is difficult to draw
and multiple channels of transmission exist (Charbonneau
& Bourrat 2021; Bourrat & Charbonneau
2022). 


### 5.3 Origins of Replicators



Another challenge to the replicator/interactor approach to evolution
by natural selection is to see replicators themselves as a
*product* of natural selection rather than as a necessary
starting point. One premise of this argument is that some form of
natural selection must have occurred on entities that initially were
not replicating, perhaps not even reproducing. This is recognized by
Dawkins, who notes in passing in the second chapter of *The Selfish
Gene* that "Darwin's 'survival of the
fittest' is really a special case of a more general law of
survival of the stable" (Dawkins 1976: 13) and that life
originated from selection of molecules for stability.




![a diagram with two parts, the first consists of a black circle labeled '0.75' with arrows pointing to three black circles below labeled respectively '0.8', '0.8', and '0.95', below this is a legend stating 'Average: 0.85'. The second part consists of a black circle labeled '1' with arrows pointing to four black circles below labeled respectively '0.8', '0.8', '1', and '1', below is a legend stating 'Average: 0.9'. below all is an equation](low_herit.svg)

(a) Population in which there is no replication and a low heritability
(\(h^2\)), yet evolution by natural selection occurs.




![a diagram with two parts, the first consists of a black circle labeled '0.75' with arrows pointing to three black circles below labeled respectively '0.5', '0.75', and '1', below this is a legend stating 'Average: 0.75'. The second part consists of a black circle labeled '1' with arrows pointing to four black circles below labeled respectively '0.75', '0.75', '1.25', and '1.25', below is a legend stating 'Average: 1'. below all is an equation](high_herit.svg)
  


(b) Population in which there is no replication, yet heritability is
1. Evolution by natural selection occurs.




Figure 3. Illustration of the idea that
evolution by natural selection can occur without replication.




The idea that selection can occur without there being replicators was
first introduced as "chemical selection" in line with the
views of Oparin, who proposed that coacervates (colloidal droplets)
could encapsulate protobiological chemicals and self-replicate without
genes through mechanical fission, a view also independently proposed
by Haldane (Oparin 1936 [1938]; Haldane 1929; see Kolb 2016).
This was later extended by the work of Sidney Fox, who showed that
proteinoid spheres could mechanically reproduce stably (Hsu & Fox
1976).



If modern biological systems evolved from molecules that did not have
the ability to reproduce, let alone replicate, one might ask: what is
the simplest case of evolution by natural selection? It is a case in
which different types of entities have different persistences but do
not produce any offspring. In this model, the types with the property
of persisting longer represent an increasing frequency of the total
population over time. One problem, though in a model of persistence
alone, is that each time one entity goes out of existence, it is not
replaced by another entity; thus, over time, the population size tends
towards zero. Although this does not mean that evolution by natural
selection cannot occur in such populations, this places important
constraints on the evolutionary dynamics of this population (Van Valen
1989). Further, it is possible to regard the ability for a population
to maintain its size or increase its size as a primordial form of
adaptation. This idea casts some doubt on the view that paradigmatic
cases of evolution by natural selection require a
population of entities that reproduce, a view championed by
Godfrey-Smith (2009). Several authors, following in Van Valen's
footsteps, have recently argued that important cases of evolution
by natural selection must involve reproduction, and that differential
persistence with or without differential growth can be sufficient
(Bouchard 2008, 2011; Bourrat, 2014; Charbonneau 2014;
Doolittle 2014; Doolittle and Inkpen 2018; for a review, see
Papale 2021). Nonetheless, assuming a metapopulation, it is clear
that populations with the ability to maintain or increase their size
would out-compete those that are unable to do so. Thus, the ability
for a population to sustain its population size might be regarded as a
primordial form of adaptation without which other adaptations would be
almost impossible to evolve.



A next "stage" in the evolution from primordial
entities unable to reproduce to modern biological systems might thus
have been for entities to produce new offspring entities (or multiply)
without the ability to pass on their properties reliably. In such a
situation, the size of a population could be maintained. The most
extreme form of that would be to imagine a population of two types in
which each type has the same probability to produce an offspring of
the other types as its own type. With entities of the two types having
different persistence, a modest form of evolution by natural selection
is still possible. Versions of this model have been proposed by
Wilkins, Stanyon, and Musgrave (2012), Earnshaw-Whyte (2012), and
Bourrat (2015a). Since there is, on average, no more resemblance
between an offspring and its parent than any other entity of the
parental generation, and evolution by natural selection is still
observed in such a scenario, one might think that heritability is,
strictly speaking, not a necessary condition for evolution by natural
selection.



Wilkins et al. (2012) argue that, over time, in a reactor with limited
incoming chemical species, hypercycles (as defined by Eigen et al.
1991) of reactions will tend to include reaction types that are more
stable and capture more source molecules and energy than variant
reaction types, leading to the evolution by natural selection of
replicator-like molecules as well as energetically efficient
"metabolic" molecules. Recent work in biochemistry has
added strength to that suggestion (Altstein 2015). Hence, given that
no replicator is required for selection (in this case, chemical),
replicator molecules can be seen as the *outcome* of selective
evolution, not a necessary prior condition for it. In effect, the
evolution of replicators is the first major transition of evolution,
despite the view of Szathmary and Maynard Smith that
replicators needed to come first (Maynard Smith & Szathmary
1995; Szathmary & Maynard Smith 1997). Bourrat
(2014) further developed this idea into a series of agent-based
models. He showed that replication is an attractor in populations
lacking heritability once small random mutations increasing or
decreasing the fidelity of character inheritance are introduced.


### 5.4 Reproducers



The works on the origins of replicators tie in with the notion of
the *reproducer* proposed by Griesemer (2000a,b, 2002, 2005;
Wimsatt & Griesemer 2007), although it was published first, based
on a circulated manuscript by Griesemer, by Szathmary and
Maynard Smith (1997). A reproducer is an entity that develops and has
a material overlap between the "parent" and
"progeny". This causal relationship between parents and
progeny is called "progeneration", the "increase in
numerically distinct objects of a given kind". Reproduction is a
composite process of development and progeneration, leading to objects
that are themselves capable of development and progeneration. Thus,
the reproducer concept extends the notion of a developmental
system.



Here, inheritance is a *system* property, not a property of
parts, unless they are also reproducing systems, and is
developmentally acquired. Organisms do not arise already capable of
reproduction in the main, but must undergo orderly transitions before
they may reproduce.



The relation between reproducers, and replicators and interactors,
varies according to author. Griesemer treats replication as the
terminal form of reproduction, once coding mechanisms have been
evolved, which is itself an evolved form of multiplication (Griesemer
2000a: 76). Unlike Dawkins' replicator concept, which Griesemer
believes is based on a similarity relationship of
"copying", a reproducer requires *material overlap*
of systems. However, replication arises when material overlap evolves
progeneration, and progeneration evolves a codical inheritance system,
as
 Figure 4
 indicates.



![title is 'Modes of Multiplication'. This is a tree diagram. At the top is a node labeled 'Multiplication' below and to the left is a node labeled 'Copying' with the line connecting labeled 'nonmaterial overlap (property transmission)'. Below and to the right is 'Progeneration' with the line connecting labeled 'material overlap (parts transfer)'. Below 'Progeneration' is 'Reproduction' with the line connecting labeled 'material overlap of mechanisms of development'. Below 'Reproduction' is 'Inheritance' with the line connecting labeled 'material overlap of evolved mechanisms of development'. Below 'Inheritance' is 'Replication' with the line connected labeled 'material overlap of evolving coding mechanisms of development'. ](replication.svg)

Figure 4. Wimsatt and Griesemer's
reproducer concept (Wimsatt & Griesemer 2007, 268).




Others, particularly Jablonka and Lamb (2005, 2007), think that
reproducers are distinct from replication and that some
epigenetic inheritance systems are reproducers without being
replicators. For them, a reproducer is the "target of
selection" [see the entry on
 inheritance systems].



Godfrey-Smith (2009: 83; see also Okasha 2006: 14) takes issue with
Griesemer's requirement of "material overlap" as
being too narrow a definiendum of reproducers. He thinks that
reproducers need not contribute actual material to their progeny
(where they template for sequences, as in the case of viruses).
Griesemer believes Godfrey-Smith has over-interpreted the requirement;
he is primarily concerned with the idea that parents *cause*
progeny (Griesemer 2014). Charbonneau (2014) furthers the move made by
Godfrey-Smith, arguing that the existence of parent-offspring
lineages is unnecessary for evolution by natural selection to
occur.



An aspect of reproducers *sensu lato* that has fascinated some
is that it does not imply a particular level of reproduction or
progeneration; indeed, Szathmary and Maynard Smith consider
that the major transitions of evolution each involve an evolved mode
of progeneration that is more inclusive or novel than what it evolved
from (Maynard Smith & Szathmary 1995; Szathmary
& Maynard Smith 1997).



Godfrey-Smith also proposed a taxonomy of reproducers, dividing them
into simple, collective, and scaffolded (Godfrey-Smith
2009: 87ff). Simple reproducers are



> 
> 
> entities that can reproduce ... using their own machinery, in
> conjunction with external sources of energy and raw materials.
> 
> 
> 



He gives an example of a bacterial cell. Collective reproducers



> 
> 
> ... are reproducing entities with parts that themselves have the
> capacity to reproduce, where the parts do so largely through their own
> resources rather than the coordinated activity as a whole.
> 
> 
> 



And, scaffolded reproducers



> 
> 
> are entities which get reproduced as part of the reproduction of some
> larger unit (a simple reproducer), or that are reproduced by some
> other entity.
> 
> 
> 



Examples here includes viruses and chromosomes. Godfrey-Smith applies
the scaffolded reproducer category to sociocultural evolution.



The notion of reproducers has also been applied to speciation and
cladogenesis (A. Hamilton & Haber 2006). While it may apply to
populations, given that taxa do not share the kind of causal unity
found in populations and organisms, it is unlikely to apply to species
or supraspecific taxa, and macroevolution in general.



Recently, Veigl, Suarez, and Stencel (2022) have extended
Griesemer's reproducer. In lieu of "reproducer", they
propose the notion of the "reconstitutor", which is a
structure that is "re-produced" at
every generation irrespectively of the causal origin of the
reconstruction. While, as presented above, the idea that
material overlap is a necessary condition for an entity to
be a reproducer and, consequently, to be an entity involved
in a process of evolution by natural selection seems overly
restrictive, the notion proposed by Veigl et al. appears overly
liberal for at least two reasons. First, without looking
for the causal connections between entities involved in
evolution by natural selection across generations, that is, what
is transmitted, predicting an evolutionary trajectory at the level of
these entities would be difficult. Second, the idea of the
reconstitutor erases an important distinction made in evolutionary
theory between two forms of evolution: namely,
transformational and variational evolution (see Lewontin 1983).
These two forms of evolution are exemplified by change due
to mutation and changes due to selection, respectively. The
distinction between mutation and selection, along with drift, is
at the heart of population genetics and general formulations of
evolutionary theory such as the Price equation (e.g., Frank 2012, who
emphasize the distinction between "selection" and "transmission" as
two important and distinct evolutionary processes). To adopt
the reconstitutor as a fundamental evolutionary entity would
require extremely strong arguments against the view that mutation and
selection described at one level are fundamentally different
evolutionary processes or, at the very least, clear advantages
for the notion of the reconstitutor over the reproducer.


## 6. Conclusion



The idea that evolution by natural selection requires the existence of
replicators has been a very useful heuristic in evolutionary
biology, but also a way of motivating the application of an
evolutionary thinking beyond the boundaries of evolutionary biology.
We started by showing how the notion of gene can be abstracted away
from its physical basis and characterized in purely informational
terms. We then showed how Dawkins and Hull pursued this abstraction
and attempted to free the gene from its biological substrate. This
motivated responses both from proponents of the replicator concept,
who furthered the abstraction, and also critics. As successful and
inspiring as such an abstraction has been, it should not be reified:
evolution by natural selection and adaptation can occur even in the
absence of replicators. High fidelity certainly facilitates adaptive
evolution, but this might be because replicators are themselves the
product of evolution rather than necessary for it.