The
replicator: a misnomer. Conceptual implications for genetics and memetics
Department
of Clinical Chemistry, Microbiology & Immunology
Blok A,
Most
evolutionary biologists and students of evolution in general have adopted the
term 'replicator' for both genes and memes. There is indeed almost unanimous
agreement [12]. However, current genes are not (self-) replicators and, as I
will argue below, in contradiction to the current paradigm of the
RNA-replicator world hypothesis, they have never been. Thus far, I came across
only one source which defends a more correct interpretation of what genes are:
"More
pernicious, because less obvious, was the choice of the term 'replicator' for
genes and other things of which copies are made. In English, the suffix -or is
used to indicate that the root to which it is atttached falls under the
ontological category of an agent. As with the -er in 'copier', it means that
which does the copying, not the sheet of paper that we copy when we feed it
into a piece of office machinery. For the (passive) patient, in
contradistinction of the (active) agent, we use other suffixes. In ordinary
metaphysics we recognize that text gets created and modified by its author and
editor, and transmitted by its copyist, perhaps using a copier. Had Dawkins [5]
called his "replicators" "replicanda" his metaphysics would
have been somewhat more transparent, but people might not have taken him so
seriously". Quote from Ghiselin [8], in a criticism of the term replicator
as it was coined by Richard Dawkins [5]. See also [9].
Indeed the
suffix -or refers to an active agent, a processor. However, current DNA-genes
are nothing but a material instantiation of information on how to make RNA and
proteins, and perform no replication. Genes are replicated informational
molecules, unable to replicate on their own, no more than enzymes can.
Moreover, replication relies on the interaction of a whole collection of very
different genes. Accordingly, 'memes' or bits of cultural information are
processed, replicated and transmitted by human minds, photocopiers, presses,
computernetworks, etc. The original prebiotic genes are then better compared to
plasmid genes which can be exchanged freely between different bacterial cells
(processors) - OR with current memes (like printed scientific theories). They
then can be regarded as elements of a language which enabled free recombination
of different concepts, just like current scientific reasoning is possible
because of the availability of copy true bits of information (printed matter),
which can be recombined over and over again.
Partially
due to the application of the term replicator for genes and memes, it has been
overlooked that only the system cell as a whole enables self replication. It is
important to emphasize that such a self replicating system thus far originated
only once during the existence of Earth. Although it are the genes which carry
heritable information, it is clear that daughter cells also need to inherit a
minimal amount of processors, i.e. at least those enzymes which can transcribe
and translate the DNA. So, although it are genes which are responsible for
heritable information, it takes more than genes to be inherited to enable
replication of genes, to make the processing system which can do so. Moreover,
not only genes and some enzymatic processors, but also membranes have to be
inherited, since membranes are not synthesized de novo, but are synthesized
only in close connection with the existing membrane. (This points to a very
central and original role of membranes or to a 'membranes early' hypothesis of
the origin of life.)
As a
matter of fact, one could even consider new nucleotide strands as being a
phenotypical artefact, since they are the product of enzymatic activity just as
well as other cell components. Notice how this illustrates that the
genotype-phenotype distinction itself has only limited usefulness, and -
certainly at the cellular level - it occurs to be a somewhat artificial
human-made dualistic distinction [see also 7], which in itself obstructs useful
insights. One might object that for DNA-duplicates to be considered as
phenotype, there is a difference with other phenotypic traits, namely that new
DNA can be made only by using existing DNA as the mould. However, this
observation accounts as well for membranes (see above). The only difference is
the 'unlimited' [11] informational content of nucleotide molecules, but this
characteristic is unlinked to replication.
I propose
to adopt a terminology which is also used in information theory (and related
fields like cybernetics)[see also 7] and to drop words like genotype,
phenotype, replicator, interactor and vehicle, which have the disadvantage of
poorly reflecting the dynamics and interactions which occur between biological
processors and between biology and culture and which are in many cases strongly
misguiding. It is more revealing to speak of digital information processors (e.g.
polymerase enzymes) and encoded, digital information (genes). In case of
self-replicators, that is cells, both processors and digital information are
embedded in a housing which consists of structural molecules (proteins,
peptidoglycan, phospholipid bilayers, polysaccharides, ...).
From these
remarks, more useful definitions then can be put forward: living cells are the
only self replicators on Earth. Enzymatic polymerases, resp. human brains,
copiers, presses, etc. are all processors which can function as replicators of
informational molecules, resp. informational symbols. These processors are
information processors. Finally, informational molecules (polynucleotides) and
texts, ideas, words, behaviours are replicable elements of instantiated
information. For this category, we might adopt the term 'replicanda' as it has
been proposed by Ghiselin [8], although the exact translation of this Latin
term is 'that what has to be replicated'. This definition then only holds for
extant chromosomal genes, since indeed the cell is compelled to copy its genes
in order to produce cellular offspring. However, it should be noticed that,
certainly in the case of cultural information, the successful reproduction of
information processors (like humans) does not depend upon the replication of
cultural information, and therefore that there is no functional need to
replicate this information.
'Replicata'
or 'replicates' ('that what is/can be replicated') might be a more general term
for informational molecules (nucleotidic genes) or cultural bits of information
(memes) which are replicated.
In
summary, the use of replicator for gene or meme is twice erroneous: they are
not self-replicators (remark that 'replicator' is generally used to have the
implicit meaning of self-replicator) and they even are not
processor-replicators. Genes and memes are replicates or bits of replicable
information. For memetics this means that we have to ask the question why some
information is replicated more successfully by replicators like human minds and
not why they replicate more successfully than other memes. This more
scientifically correct approach is e.g. used in the paper of Heylighen [10].
Selection,
natural selection and cultural selection
These
definitions of self-replicator, replicator and replicate lead us to
considerations on the essence of natural selection as a special case of
selection. Selection is rather a tautological principle: whenever there is
variation on a theme, one of these themes will be best fitted to certain conditions,
given by the environment, which also includes the other variations on the
theme. Having different kinds of cars, one car will be best suited to reach
high speeds on a straight road, one car will be best suited for riding a curly
parcours, one car will be best suited for transporting many people, one car
will be best suited for driving and parking easily in a crowdy city, one car
will confer an image of certainty and successfulness to its owner. In case most
people live in cities and do not care too much about confirming their self
image by means of the car they own, a type of small car that enables easy
driving in the city will be sold most and will therefore be most successful
when measured by number of copies made of it.
Specific
cases of selection then can be understood by defining the theme, its possible
variations on the one hand and on the other hand the environment to which the
different possible variations on the theme will have to fit.
All of
these general considerations on what selection is hold as well for natural
selection. However, natural selection is often erroneously considered as the
only possible form of selection and it is forgotten that it is a very special
case of selection, because the selection occurs among self-replicators (that is,
cells), unlike cars, prebiotic metabolic cycles and ideas. Moreover, all the
self-replicators stem from the first system able to duplicate. Since this
duplication is not watertight copyproof, several variations on the original
theme (the first cell or the theme of self-replication) are continuously
produced, with as a 'welcome' side-effect that in most cases some of the
variations will fit to whatever environment or whatever environmental change.
In
summary, because a self-replicating system once occurred on Earth, it was
possible that the original genetic code of it - wich contained all the
necessary information on how to make the next self-replicating system, was
copied manifold. High copy fidelity, ensuring sufficient numbers of functional
self-replicators, allowed also for a number of mutants to exist. Some mutants
also could survive. Some mutants even could explore new environments or did
better in the old environment than their parent wild types. A small percentage
of erroneous descendants is an ensurance for adapting to previously not
inhabited environments or for adapting to the changing environment.
These
considerations stem from an information centered approach which leads to more
generally applicable insights than a gene centered one.
Natural selection
is about the replication of informational molecules whereby the replication of
the information depends on the functionality of the organisms, i.e. the genetic
information processors for which the information encodes. The fitness of the
phenotype is also the fitness of the genes, and vice versa. Cells are
metabolically open, but semantically closed systems. From this definition the
difference with cultural information becomes obvious.
Just like
variable genetic information and variable information in general, variants of
cultural information are selected as well. I referred to this as a tautology.
For
example, different scientific theories are weighed by the scientific community,
whereafter finally one or still a third, or a recombination of still another
five ideas appears to solve best the problems tackled and is replicated more
successfully than other theories. The difference with natural selection is that
the defenders of one theory - the scientists, the information processors - do
not die because their theory dies or that they do not produce more offspring
because they defended a successful theory. The information encoded in a meme
(usually) has no influence on the survival of the processor (a human in this
case). Vice versa, the ideas of a parent of many children are not necessarily -
certainly no longer at present - successfully replicated ideas. Scientists with
many children are not necessarily successful in spreading their theories.
Christ had no children. The evolution of cultural information does not depend
on the differential survival of its processors to proceed.
By
reversing the adagium that memes must be replicators in analogy to the fact
that genes are replicators into the statement that genes are replicates just
like memes are, we can further suggest that genes were also replicates in
prebiotic life. This suggestion contradicts the current paradigm that life
evoled by competition between self-replicating RNA-molecules, whereby the cell
gradually evolved around the fastest self-replicating RNA-molecules by means of
natural selection, i.e. as a consequence of the differential reproduction rate
of different self-replicating molecules. We propose to postpone natural
selection till after the origin of the first chromosome containing cell (the
first self-replicator) and to consider how a much more flexible and powerful
kind of memetic evolution took place, comparable to what is happening since the
origin of symbolic language in the animal world.
(It should
be noticed that this does not mean that we have to dismiss the several exciting
findings of RNA-research [e.g. 3,14] nor that we disagree with the 'nucleotides
earlier than complex proteins' hypothesis. Only, we propose to consider these
findings from a different point of view.)
Symbolisation
of information thus far has occurred twice on Earth. Prebiotic life developed a
manner to encode information (symbolisation) into informational molecules
(nucleotide strands). In biology, informational communication first took a
nonchemical way of transmission with the advent of neuronal brains in animals
which could make use of nonmaterial sound wave energy and photonic energy
(vision) to transmit information (the origin of memes), whereafter strong
symbolisation of this nonmaterially transmitted information has occurred in
humans by the development of spoken language. This has finally led to the
re-entry of material substrates which could carry information as visual
symbols, in the form of written language. I will argue that the initial role of
nucleotides is comparable to that of written language. While nucleotides
enabled to encode chemical interaction, symbolic language enabled to encode
behavioural interaction.
The
essential thing about encoded information is that it can be mixed, recombined,
merged, over and over again, because of the fact that it is not a metabolic
process but a code on how to perform such a process, which has the virtue that
the information is not transformed (only transcribed or translated) during
interaction. It is impossible to mix processes: One can't mix the activity of
enzyme x with that of enzyme y, one can't take the bacterium E. coli and mix it
with a piece of human tissue, while keeping a functional process, one can't mix
the ideas of two people by mixing their brains.
But what
if these processes also are encoded somewhere? Evolution has managed many times
to combine the functions expressed in different modules of enzymes with each
other. This could be done because there was a genetic code for it and by
recombining parts of this code, something completely new, composed of already
existing components but arranged in a different manner, could emerge. Similarly
we can mix the eubacterium Escherichia coli with human enzymes, by inserting
into its genome the code for such a human enzyme (e.g. for the production of
insuline for diabetes patients).
We can mix
different ideas since they can exist as a memory in our mind. This process is
largely enhanced by the availability of written records, since this provides a
more faithful, copy true back up. One can mix as many of these ideas as one can
gather (e.g. by reading). Many different lineages of information can
continuously come together. Sometimes (but apparently rarely) this leads to new
useful insights. Furthermore, it takes only one processor and one template to
make an unlimited number of copies of encoded information, something which is
not achievable when dealing with processes.
The
following is just a brief exercise of how we could envisage analogies between
'memetic' evolution towards the origin of the genetically encoded cell and
present day cultural evolution (which may or may not lead to a novel kind of
'memetic' self replicator, e.g. some kind of self-assembling, duplicating robot
as suggested by Tipler [13]).
Not in
contradiction with some current thinking [e.g. 6] we assume the existence of a
premetabolic network of interacting chemical molecules, organized in smaller
networks of heterocatalytic cycles, mostly embraced by membranes. Such a
membrane with its internal metabolic cycling can be called a protocell (which
is devoid of genetic material), which interacted intensively with other
protocells and/or free-'living' cycles and available molecules. The prebiotic
system as a whole can then be compared with the current ecological network,
which is composed of interacting genetically encoded organisms of different
complexities.
The basic
proposition of this paper is that symbolisation of chemical interaction
(communication) between these protocells and/or parts of their internal
networks is suggested to have been the original function of nucleotidic
information. Instead of direct metabolic interactions (comparable to direct
behavioural interaction between animals), some cells also started to make use
of informational molecules, which not directly took part in the interactions
but which nevertheless could influence the behaviour of other protocells (or of
intracellular cycling), just like symbolic sounds or written texts can
influence the behaviour of other humans (or of 'intrapersonal' thinking).
(Remark that information has been defined as “a difference which makes a
difference to 'someone' else” [7].)
Written/printed
information, just like nucleotide information, can than be used without being
transformed (i.e. analogously processed) during this interaction: it is
digital.
With
respect to the evolution of information, the chemical cycling within protocells
is best compared to the animal body, performing metabolically essential
functions. The membrane is best compared with the neural system (incl. brains
and perception organs) of animals, since it performs interactive, communicative
functions. Like some of these protocells started interacting by means of
symbolic molecules (informational molecules, stretches of nucleotides), some
animals (humans) started interacting by means of symbolized gestures and
sounds. This leads to new interactions, also with nonsymbol using protocells
(accordingly with other animals, ..., bacteria). E.g., this symbolic
information may have enabled the symbol using protocells to use metabolic
energy from simpler protocells, like humans started to use animal power. This
is to be regarded as some kind of symbiosis, since both symbol using and
nonsymbol using protocells can have metabolic profit, like the number of horses
increased correspondingly with the number of humans.
(Remark
that an inadvertent outcome of this kind of reasoning is that this story is
about symbiosis and mutual profits, in contradiction to the 'natural selection
early' approach whereby the selfish fastest replicators won the game.)
While the
informational molecules may have been internalized and processed at first in
order to create new ones (like humans process words in an analogous manner:
transformation), the interaction between protocells and informational molecules
may have lead to the production of external processors (metabolic and
informational enzymes). Similarly, humans aided by words have produced
different external metabolic processors (wheels, ploughs, tractors, factories)
and information processors (pens, type writers, presses, copiers, computers).
Because in
this model the replication of informational molecules presupposes only the
ongoing of metabolic activity in general and thus not depend on the direct 'survival'
of some particular protocell - unlike in e.g. models of molecular
self-replicators and chemotons [11] and unlike present day chromosomal genes,
both cases where the fate of the informational molecules is tightly linked to
that of the metabolic efficiency of its cell - a lot of recombinatorial freedom
was available to prebiotic chemistry. Similarly, cultural information can be
recombined in an at random manner, whether or not this leads to silly ideas
(like this one!?), because it is not linked to the fate of the replicators
(human brains, computers). In fact the interaction between protocellular
membranes, nucleotide encoded information and extracellular processors may have
enabled to produce large extracellular heterogeneous protochromosomes, just like
the interaction between humans and printed code and external information
processors like presses and computers resulted in the production of scientific
theories and complex machines.
The whole
community of (simple protocells and) symbol using protocells became more and
more dependent on the usage of external informational molecules and external
informational and metabolic processors. The same happens in our present
society, which would collapse at once when language, printed information,
production machines or computers were taken away. In the end, most metabolic
functions and most information processing were done by digitally processing
external enzymes (e.g. polymerases), so that the role of the original
protocells was merely a motivating one. Accordingly, humans are less and less
needed to keep the information processing going on. We put in a search string,
push some buttons and the world wide web searches the relevant information. We
are more and more needed only as motivators. Current co-enzymes (motivators of
enzymatic activity) accordingly can be regarded as remnants of the original
premetabolic protocells.
Finally,
protocells consisted of a membrane, probably flattened since at this stage it
contained only few internal chemical cycles, with an externally attached
DNA-protochromosome - consisting of genes encoding for very different functions
- and some externally attached enzymes and RNA-molecules. At several occasions
such membranes may have 'gastrulated', whereby the chromosome and the enzymes
and possibly some external medium with free enzymes and other molecules were
internalized (in accordance with the obcell theory [1,2]). At one such occasion
the enclosed informational molecules and processors contained all the necessary
information and functionality to produce a self-replicating system (remark that
reverse transcriptase was not enclosed). A similar event has not yet happened
in culture (self-assembling robots [13] are just one imaginable outcome).
While explaining
the origin of life as a memetic process, this approach also might provide a
unifying theory for the evolution of information, whereby at two events
symbolisation of information occurred - once of chemical interaction, once of
behavioural interaction - and whereby at one occasion this encoding lead to a
chemical self-replicator (the biological cell), a memetic evolution which seems
to be happening again.
This
symbiotic approach may circumvent many of the current problems like the
'chicken or egg' problem of DNA/RNA/protein interaction, not (yet) solved by
the RNA-replicators world hypothesis. It also more easily explains how a
chromosome consisting of very different functions, and whereby none of these
genes by theirselves contain sufficient information to cover the complex
process of self-replication, can have originated. It circumvents Eigen's
paradox whereby different self replicators outcompete each other when brought
together in a cell, instead of merging into a chromosome (Eigen's paradox is solved
(?) only by the rather artificial stochastic corrector model [11]). The much
faster and flexible memetic (cultural) evolution also might resolve the time
window problem (whether real or not [see 6], which lead some eminent biologists
to adopt an extraterrestrial origin of life [4]. Of course, this 'memetic
origin of life' hypothesis poses its own problems.
References
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