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Evolution and Persistence
Aryn Conrad & Carlos Mariscal
Abstract
There are persistent entities like clonal species, chemical systems, or cultural
entities that seem to adapt to their environment without reproducing. Since the
standard account of evolution is given in terms of reproduction, according to a
strict interpretation, they are not evolving. In this paper, we develop an
expanded understanding of the standard account of evolution to accommodate
persistent entities.
We begin by detailing concerns that the standard account of evolution is not
adequate for various biological systems (e.g. clonal species and colonial
species). We discuss two attempts to produce a generalized theory of evolution.
Then we relate a major objection given by Kingsbury 2008, which points out
that persistence accounts are committed to accepting the seemingly absurd case
of rocks on a beach as an evolutionary system. We present our theory, which
accepts that evolution is not an all-or-none process; evolution can come in
degrees. So rocks on a beach are weakly evolutionary. With that in mind, we
give an account of what it takes for a system to be strongly evolutionary. We
take our view to accommodate all biological, cultural, and chemical
evolutionary systems while adequately explaining the phenomena in each. This
reduces much of biological evolution to a special case of the broader process of
evolution.
I.
Introduction: The standard account and its discontents
Lewontin, following Darwin, gave the following conditions for adaptation:
(a) Variation – “different individuals within a species differ from one another
in physiology, morphology and behavior”
(b) Heredity – “variation is in some way heritable, so that on the average
offspring resemble their parents more than they resemble other
individuals”
(c) Natural Selection – “different variants leave different numbers of offspring
either immediately or in remote generations”
(d) The Struggle for Existence – “Variations that favor an individual's survival
in competition with other organisms and in the face of environmental
stress tend to increase reproductive success and so tend to be preserved.”
(1978, p. 220)1
Lewontin is best known for his 1970 paper that has a slightly different list: phenotypic diversity,
differential fitness, and heritability of fitness. We think that the causal linkage between variation and their
fitness is crucial for any understanding of adaptation, so we include (d) here.
1
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These conditions are generally regarded as uncontroversial. Notice that
according to this account, reproduction is an essential part of evolution by natural
selection. By extension, only organisms that reproduce can have adaptations
produced by natural selection.
Most of the time, the standard account works well for biologists and others who
use biological abstractions. Even those who study cultural evolution generally treat
cultural variants or memes as reproducing entities. (See Boyd and Richerson,
Laland and Brown, Dawkins, and Milikan in LTOBC.) But there are some tricky
cases. Section II covers some of these cases. In section III, we discuss Frederic
Bouchard’s work, which draws heavily on these tricky cases. Bouchard diagnoses
the problem as being overly focused on reproduction rather than survival. If
reproduction is understood as merely one of many ways genes or lineages can
survive, then a survival-based account of evolution will be more accurate.
Bouchard believes his account does this. We also discuss Justin Garson, who also
proposes a moderate approach, which allows for persistence and reproduction.
Section IV discusses an objection by Justine Kingsbury applies to both Bouchard
and Garson’s accounts. Section V presents our view in which we reject the
implications that Kingsbury thinks follow from her thought experiment. Instead,
we proceed to diagnose what the standard account misses: a more complete
interpretation of variation. We take our account to apply to evolutionary systems of
any sort, anywhere, not merely biological evolution. We end with plans for future
work.
II. Tricky Cases
For most organisms, the distinction between growth and reproduction is
straightforward. Growth is when an organism increases in size, amount, or energy
available for expansion. Reproduction is when an individual splits into two or a
sequestered germ line goes through a one-cell bottleneck and a new, separate
individual is produced. But for some creatures, the distinction between growth and
reproduction is not so neat as reproduction is not always the primary means of
propagation. Quaking aspen primarily propagate by sending out root stems. From
these stems grow individual trees called ramets. The collection of the ramets
connected by a root system is called a genet and constitutes one organism. They
rarely reproduce via seeds. The oldest stand, Pando, is 80,000 years old. It may not
have flowered for over 10,000 years (Einspahr and Winton 1976, Mitton and Grant
1996).
Now, consider the following:
Two genets, A and B, live in the same environment. For simplicity, they are
both female so they cannot mate with each other. One of the ramets in A mutates
in a way that allows it to better draw water out of the air. Over time, the
environment becomes drier so that both the non-mutated ramets of A and B
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eventually die off. But, the mutated portions of A live on. Intuitively, it seems as
though A has been selected over B and moreover, that A has done better than B.
Indeed, the mutation could be called an adaptation to the drier environment.
Strictly speaking, however, this scenario does not fit the standard formulation as
no reproduction has taken place. There has only been differential persistence. In
this case, selection is acting on parts of a growing individual, not a population of
individuals.
The case is easier in the cultural realm. Consider what goes on in the case of
companies. Companies compete with each other. Some go bankrupt, others thrive,
and some just continue scraping by. But rarely do they seem to reproduce. When
they do, it is often because they are forced to split. Typically the goal of businesses
is not to multiply, but to grow.
Perhaps there is some sense in which companies reproduce: after they go
bankrupt their ideas, employees, stakeholders, and assets disperse to new
companies. But this sort of reproduction is not the sense in which we usually
determine a company’s success. Instead, a company’s success is described in terms
of profitability, persistence, and influence. The proliferation of a company’s ideas
might be of interest to those who study cultural evolution, but it does not seem to
be the best way to measure a company’s success. Certainly it is not the way
economists conceive of successful companies. Luckily, there are other ways the
Darwinian approach can be applied.
Consider two companies, R and S, that want to expand into a new market–
developing nation Y. They both sell small consumer electronics and are in direct
competition. After doing their market research, both companies decide on a plan of
action. R markets directly to women, figuring that although Y’s society is
patriarchal, women will be the most likely to generate demand. S banks on the
patriarchal nature of the nation, and markets to men, trying to appeal to prestige
biases. R’s strategy works well and they make good profits. S, on the other hand,
goes bankrupt. It seems like a Darwinian perspective is useful here– R was selected
over S.2 Moreover, it seems like the marketing strategy was well adapted to the new
environment. But it will not fit the standard model as neither R nor S reproduced.
R succeeded over S in two ways: it persisted longer and it made more money. But
profits are not offspring and persistence is not allowed as a measure of fitness.
Companies and aspen are not the only entities left out in the cold by the
standard account. Other persistent entities have spurred some to try to reformulate
the standard account. In the next section, we will describe two of these accounts
and show how they are persistence accounts. Next, we will present problems for
The fact that companies designed their strategy is not anti-Darwinian. The only design that is antiDarwinian is the omniscient design of the pre-Darwinian God. This is merely a case in which variation is
not blind as in organismic biology, but near sighted (Mesoudi 2006).
2
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these accounts. In section V, we present our account, in which we reconsider each
of the criteria highlighted by Lewontin.
III. Other Persistence Accounts
For the past decade, Frédéric Bouchard has challenged the received view of
evolution with his own persistence account. He points to cases such as the Quaking
Aspen and termite colonies to highlight how the standard account fails to
adequately explain cases of adaptation in which no reproduction takes place.
Bouchard hones in on the role of fitness, pointing out that some tricky
biological cases cannot be satisfactorily accounted for if we define fitness as
differential reproductive success. Bouchard instead proposes an account of fitness
in terms of survival. His own view is to define fitness as a propensity toward
Persistence Thru Time (PTT). His account defines fitness roughly as follows:
(Lineage) X is fitter than (lineage) Y if X has a higher propensity to persist
for Z amount of time than Y. (2011 p. 16)
The PTT account of fitness is intended to fit every case of adaptation. Mitotic
cell division of single-celled organisms, sexual reproduction, and unusual cases like
the Quaking Aspen are accounted for in terms of their propensity to persist
through time. In some cases, the lineage is defined in terms of reproduction, in
others persistence and growth is sufficient.
Bouchard’s account is of a singular criterion for fitness: growth and
development are relevant to fitness just in case they increase the propensity for a
lineage to persist. Bouchard’s motivation for a unitary account of fitness seems to
be methodological: we should attempt monist approaches before proceeding with
the assumption of pluralism. If one assumes that a phenomenon is not unified, the
phenomena will remain disparate.
Bouchard’s account is radical. Looking back to the list that began this article,
Bouchard can be viewed as implying the following reformulation of Lewontin’s
original account of adaptation:
(a)
(b)
(c)
(d)
Variation
Heritability (in the form of persistence, presumably)
Differential Persistence Through Time (PTT)
A Causal Connection between (a) and (c).
According to Bouchard, by changing our concerns from reproduction to survival
in (c), we can account for all of the relevant cases we mentioned in section II, as
well as many more. One virtue of Bouchard’s view is that persistence certainly
seems to be the ideal candidate for a unitary conception of fitness. Persistence
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seems to be a necessary feature for evolutionary success. If a lineage does not
persist, ceteris paribus, then it is not fit.
Bouchard is not the only person to propose a persistence-based account of
adaptation. Focusing on rather different sets of issues, Justin Garson is interested
on the differential retention of some neural connections over others. With an eye
on the mental content debate, Garson recommends this reformulation of the
Selected Effects account of function:
The function of a trait consists in that activity that historically
contributed to its being differentially reproduced or differentially
retained within a biological system (555).
Garson’s Generalized Selected Effects Theory of Function implies the following
reformulation of Lewontin’s original account of evolution by natural selection:
(a)
(b)
(c)
(d)
Variation
Heritability
Differential Reproductive Success or Retention
A Causal Connection between (a) and (c).
Garson’s account, because it is tailored to fit neural selection, does not
specifically deal with heredity. He must at least accept an account of similarity over
time in order for the persistence cases to fit. We will return to this later. A key
feature of Garson’s account is the differential persistence of a trait. Without this
requirement, the account falls prey to a number of counterexamples. For example,
Marc Bedau has an example of a twig floating in a stream that brushes against a
rock and creates a backwash that contributes to it remaining pinned against the
rock (Bedau 1992). The problem with the twig example is that creating a backwash
contributes to its own persistence, yet it doesn’t seem to be an adaptation. But this
does not fit Garson’s account because here there is no differential persistence. The
twig backwash is not the fitter backwash in a population of backwashes. This new
formulation looks promising as well. In the next section we will see that both
Bouchard and Garson’s account face serious objections.
IV.
Objections
A formidable objection to both of the previous accounts is mentioned in
Kingsbury (2008). Imagine a rocky beach. Some of the rocks on the beach are
harder than others. When the waves crash on the beach, the harder rocks are less
likely to break up than the others. Eventually, the softer rocks are so broken up
they cease to exist.
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This situation fits the requirements of both views. For Bouchard’s theory, the
harder rocks have a higher propensity to persist through time compared to the
softer rocks. Bouchard, however, is not committed to allowing evolution to apply to
the realm of the non-living, and can respond by denying non-biological cases.
There are two problems with this approach, however. First, biological cases can be
constructed to produce this exact same problem. One can imagine a dystopian
future composed entirely of infertile, non-growing Quaking Aspens. On Bouchard’s
account, the sturdier ramets are expected to survive longest. So Bouchard is
committed to saying the sturdiness of the Quaking Aspen is an adaptation, much
like the hardness of the rocks. The second problem is that there is nothing
explicitly stated in either Bouchard’s account nor the standard account that
requires entities to be alive in order to undergo evolution by natural selection. Nor
should we be committed to this without consideration. Are viruses, for example,
considered alive? They certainly evolve according to the standard account. Prions
make the case even murkier. Depending on how Bouchard defines life, he might
have to deny that viruses or prions evolve in his account.
Bouchard’s theory fits the rocks on the beach case as described by Kingsbury.
So, too, does Garson’s theory. The population of rocks on the beach has variation
and some kind of historical continuity. They also differentially persist and there is a
causal connection between the differential persistence and the relevant variants.
That means that the rocks are, on persistence grounds, evolving by natural
selection. This also commits views about persistence to the claim that the hardness
of the rocks is an adaptation to their environment. This seems highly
counterintuitive to many people. Clearly, a good account must either avoid this
conclusion or explain how it can be acceptable. We take the latter route.
V.
Adapting Persistence: Our Account
a. A map of our project
In this section, we lay out our account of evolution by natural selection. We do
not want to reject the standard account- merely expand it. We will keep Garson’s
important move: differential persistence is key- mere persistence is not enough.
Our account also makes minor modifications to the other Lewontin criteria. We list
them here and explain them in the following sections:
(a)
(b)
(c)
(d)
Populational or Individual Variation
Historical Continuity
Differential Success3
A Causal Connection between (a) and (c).
Persistence will always be a measure of success, but something like differential reproduction or growth
will also apply. Consider the case of companies in which success can be measured by profitability as well
as persistence. Profitability seems to be a growth-like measure.
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Notice that we make no changes to (d) and we only make minor changes to (c).
In order to solve issues with (c), we must modify (b) to avoid discussing evolution
in terms of objects with discrete generations. We use what is a very minimal
condition of historical continuity. Evolving individuals like biological species are
historically continuous with themselves.4 In many biological cases, this is achieved
using discrete generations, but these are special cases–not required for a general
evolutionary account. Interestingly, the bulk of the work in our account is done by
expanding (a): the notion of variation. We will start by briefly responding to the
two objections Bouchard and Garson’s accounts faced.
b. Biting bullets: Evolution is a matter of degree
Our first move is to bite the bullet on the rocks on the beach example, although
perhaps “nibble” is a better word. We think that evolution is a matter of degree. On
the evolving end, you have rich evolutionary systems like organisms and culture
that produce a strong fit of organisms to their environment. On the minimal end,
one can imagine a bunch of Helium atoms in a vacuum. They aren’t evolving in any
intuitive sense.5 The rocks on the beach are on the weak end of evolution, but they
still count as an evolving system– albeit a boring one.
Systems can vary with respect to how much variation occurs, how heritable
certain features are, and how much selection is present, not to mention that the
environment also varies. So it shouldn’t be surprising that the strength of an
evolutionary system should also vary. Something similar to this could have
happened early on in the history of life. Perhaps we could say, “In the beginning
were the chemicals, and the chemicals persisted differentially.” Replicators might
have appeared de novo, but perhaps they did not. To define the possibility out of
existence is to beg the question of how life originated. The important point is that
whether or not something is evolving is a matter of degree. From systems that are
merely weakly evolutionary can come strong evolutionary systems like those we see
today. This picture allows for gradualism about many aspects of evolution
including selection, adaptation and function.
c. Two kinds of variation
There are two kinds of variation in a selection process. They are not unrelated,
but they are distinct enough that we think of them as two separate spectra on
which a given system may vary. That is, a system may be low on one and high on
While we have contingent answers to the metaphysical concerns of continuity and persistence, to
address these fully would greatly derail the present proposal.
5 Robert Brandon pointed out to us that the Helium atoms are still moving around and are thus varying
with respect to position. So in this respect, some very weak, very boring, sort of evolution is possible.
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the other or vice versa, even if it is hard to find a good instance of one being
entirely absent. One is at the level of populations and the other is at the level of
individuals.
i.
Fresh Populational Variation
One kind of variability displayed by strong evolutionary systems is the capacity
for fresh variants to enter the population. Consider the rocks on the beach. New
individuals may enter the beach– that is, new rocks may be delivered by streams or
lava flows, but these rocks are not more likely to be adapted to the beach than the
rocks that came before them. The population of rocks will not increase in diversity
as a result of these new rocks. On the other hand, new variants can enter a
population of vertebrates via immigration, mutation, recombination, and plain old
sexual reproduction, among other things. Evolution cannot create anything new in
the case of the rocks, but it can in the case of organisms.
ii.
Individual Mutability
Like rocks, vertebrates cannot vary themselves as individuals, at least not
much. The majority of the variation is seen in their offspring. But some things can
change themselves internally. For example, companies can. One of our favorite
examples is that of Nintendo, which started out as a playing card company in 1889
and now makes video games and consoles. Companies are an example of
individuals that are highly mutable. Similarly, biological lineages can be mutable as
well. Consider DNA as conceived of by Dawkins- this is a lineage that persists as a
historical entity. As a lineage, it displays a high degree of mutability. However, if it
is conceived of in this way, there is a sense in which it is not truly a reproducer, but
a persister. The lineage that is DNA persists through the organisms that contain it.
Reproduction is merely a way in which it persists and spreads.
This may sound familiar to philosophers. It is related to the type/token
distinction. The entities in a lineage are a sort of token, and lineages are a special
sort of type. Both of them are historical in nature. Notice that this requires a
change to the heredity condition. Individuals that persist do not display heredity,
as conceived of in terms of discrete generations, but they do display historical
continuity. Lineages that reproduce also display historical continuity.
Table 1
High mutability
High Fresh Companies
variation
DNA
Biological Lineages
Low Fresh 100 proteins
variation
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Low mutability
Paintings
Individual vertebrates
Rocks
Helium atoms in a vacuum
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iii.
The interrelationship
The two kinds of variation just described are interrelated. Philosophers
committed to treating populations as historical individuals might even say they
describe similar phenomena at different levels. Together, these kinds of variation
are exhaustive but not exclusive. The two kinds of variation are related because
almost any degree of individual mutability allows for fresh variants to enter the
population. Any pure examples using only one kind of variation therefore tend to
sound very contrived. Here are our best two attempts:
1. Paintings
New paintings constantly enter the population of paintings, but few paintings
change in makeup over time. Nevertheless, it is difficult to deny that the paintings
have changed over time and that new paintings are typically influenced by the work
that came before them. Thus, the paintings throughout history are high on the
fresh variation spectrum but low on the mutability spectrum.
2. 100 protein conformations
Consider a population of highly mutable proteins that can be in any one of 100
conformations at a time, but cannot change beyond that. This is a population of
highly mutable entities but allows for no fresh variants. Once the population has
explored all of the 100 conformations, any change in conformation will not be new
to the population.
This example is more contrived than the first one. That is because mutability
leads almost inevitably to new variants entering a population. However, you can
have new variants enter a population without any of the constituent entities being
mutable. The paintings example is meant to illustrate that.
Notice that both of these populations can evolve. Both selection and drift can
act within them. The population of paintings can and has evolved over time. Within
the example of proteins, the frequencies of conformations can change. One
conformation could even go to fixation. But beyond this, there is little room for
evolution. This illustrates the primacy of fresh populational variation for strong (or
rich) evolutionary systems. Individual mutability is important, but it is important
primarily because it introduces new variation into the population.
d. More likely to succeed
We want to say a brief word about how the concept of fitness changes on our
account. Since reproductive success is not always an option for the entities we are
considering, we would like to present the following account:
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Fitness: A is fitter than B in E iff A
is more likely to succeed than B in E.
There are many different
measures of success. The answers to
questions about these will always be
objective.
Which
ones
are
interesting is determined by the
scope of the discipline being used to study them. However, persistence is almost
always a measure of success for any persister—not so much for reproducers. For
them, the success is reproductive
Figure 1
success. But notice that our
account helps explain why surrogates for fitness–like caloric intake and so forth,
can be good measures.
Consider the two grasses in Figure 1. At t1, they cover the same amount of
ground. At t2, grass A has expanded to cover much of the world, but grass B
remains about the same. However, at t3, grass A has gone extinct. Grass B remains,
and persists for a very long time. There seems to be a sense in which A was more
successful than B, and another sense in which B was more successful than A. We
could substitute trilobites for A and horseshoe crabs for B, using the same
intuition. Persistence is one kind of success, but it is not the only one.
Another possible substitution is companies. Consider two companies. One
makes a spectacular amount of money, but goes bankrupt. The other goes along,
sure and steady. There are different kinds of success here. Persistence is one, but
once again, it’s not the only game in town. With companies, profitability is very
important. Investors and economists care more about this than mere persistence.
Other systems might show other kinds of success.
VI. Future applications and unresolved questions
a. Drift
We think persistent entities can evolve by drift, but at this point have not yet
worked out how that is. Initially, we want to say that cases of drift will fulfill a-c,
but d will be absent. We suspect that all evolutionary systems will tend to drift
(Brandon 2006).
b. Metaphysics
As stated earlier, there are many metaphysical issues that arise in this discussion.
We recognize that there is a crucial persistence question left unresolved here. Our
account is about evolution and should be consistent with many possible
metaphysical views. Given the space and time constraints for this draft, we are
unable to discuss them here. We hope to address these in future work.
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c. Mathematics
Despite our most sincere efforts, neither of us is R.A. Fisher. We have not yet
worked out a population genetics for evolutionary systems that don’t have
populations. That said, the math would likely vary with each system. For most of
biology, mutation at the genetic level is the ultimate source of variation. It is
relatively straightforward to describe mathematics for evolutionary systems given
only one possibility of fresh variation. We expect the mathematics behind
evolutionary systems with significantly different forms of variation will be far more
complex.
d. Workability
We expect a major challenge to our view will be that it is not useful to working
biologists. This may be true for most, but it is not true for those working on certain
areas of biology. For example, a huge question facing biologists is the origins of life.
How do you get from non-living to living? Liane Gabora (2006) argues that early
life did not evolve through natural selection because the standard account does not
allow for the inheritance of acquired characteristics (as some models of the origins
of life hold). In our account, that is not a problem– both chemical evolution via
enclosed autocatalytic sets and biological evolution via replication are forms of
evolution. Our account will also be useful for people interested in cultural
evolution, as we have described. In the past 30 years, evolutionary approaches to
economics have become more widespread. If evolutionary theory only applies to
reproducing entities, it is unclear whether evolution can explain anything in
economics. Using our account, however, seeing economic adaptations can be more
straightforward.
VII. Conclusion
The possibility of an evolutionary account for persistent entities has remained an
unsolved issue in cultural evolution and we argue that it is problematic in regular
biology as well. Here, we have presented an account of evolution that applies to
persistent entities as well as reproductive ones. Our account allows for degrees of
evolution. As such, we accept Kingsbury’s case of differential persistence of rocks
on a beach as weakly evolutionary. Biology should teach us to expect gradation and
change everywhere. We’re not sure why this approach isn’t championed more
often. With that in place, we describe our view opposite the views of Bouchard and
Garson’s. We elaborate on the role of heritability and variation far more than
either. Understanding these elements makes us reconsider what is doing the
evolving– the population or the lineage to which the population evolves? We accept
the latter because it makes sense of evolution anywhere it takes place.
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References
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