PERCEPTIONS OF SCIENCE: Natural Enemies--Metaphor or Misconception?

[Dr. Richard C. Cassin]

Science -- Chew and Laubichler 301 (5629): 52


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            PERCEPTIONS OF SCIENCE:
            Natural Enemies--Metaphor or Misconception?
            Matthew K. Chew and Manfred D. Laubichler*
            In a recent and well-publicized case, two northern snakeheads
(Channa argus)--an Asian fish often raised for food in flooded rice
paddies--were discovered along with a cohort of fingerling progeny in a
suburban Maryland pond. State biologists all but panicked, and the media
converged on the pond for a photo opportunity to go with the news story.

            Metaphors carried the message: Snakeheads (see the figure) are
not merely foreign, they are "Frankenfish." Like other immigrants, they were
accused of immodest fecundity. State of Maryland biologist Bob Lunsford was
quoted: "It's the baddest bunny in the bush. It has no known predators in
this environment, can grow to 15 pounds, and it can get up and walk. What
more do you need? If you catch it, kill it. It's not a dead or alive thing,
we want it dead." (1). An official "unwanted" poster stated: "Kill this
fish." Nature picked up the news story (2), and Science alluded to it in a
NetWatch item (3). Each of these reports included the press release
hyperbole: land-walking, voracious, an ecological disaster.




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            Kill this fish? Channa argus (northern snakehead) as presented
by the U.S. Geological Survey (13).
            CREDIT: U.S. GEOLOGICAL SURVEY/SUSAN TRAMMELL



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            Metaphors are ubiquitous in science. Most biologists are
familiar with archdeacon William Paley's illustration for the existence of
an omniscient creator: in the same way a watch found on a beach implies the
existence of a watchmaker, the complex design of organisms implies the
existence of a designer. The popularity and persistence of this
metaphor--with proponents of Intelligent Design as well as with
ultra-Darwinists such as Richard Dawkins--lies in its simplicity and
intuitive appeal.

            Simplicity and intuitive appeal are also the main reasons why
scientific language has never succeeded in "cleansing" itself from
metaphorical "impurities," despite several attempts to do so. Indeed,
metaphors appear to be essential to all forms of language and understanding
(4). But if scientific language is by necessity to some extent metaphorical,
then interpretation of its content depends on the cultural context that
generates the metaphors that are used. And here the problems start.

            Evolutionary biologists customarily employ the metaphor
"survival of the fittest," which has a precise meaning in the context of
mathematical population genetics, as a shorthand expression when describing
evolutionary processes. Yet, outside of the shared interpretative context of
evolutionary biology, the same metaphor has been employed to argue that
evolutionary theory is fundamentally flawed. Natural Selection, the argument
goes, leads to a survival of the fittest. The fittest are those that
survive. Ergo, natural selection describes the survival of the survivors.
Thus one of the core concepts of evolutionary theory is a tautology. While
it is easy to see how such an argument represents a deliberate
misunderstanding of evolutionary theory, it also alerts us to some problems
inherent to the use of metaphors in science.

            Metaphors introduce a fundamental trade off between the
generation of novel insights in science and the possibility of dangerous or
even deadly misappropriation. The extension of genetics to eugenics owed
much of its popularity in the United States and in Germany to its use of
culturally resonant metaphors. Labeling people as a burden, a cancerous
disease, or a foreign body (Fremdk?rper) conveyed the "threat" to society in
terms that people could relate to in their respective historical and
cultural settings (5-8). Given this power of metaphorical language, it is
understandable why several scientists have been concerned with the
prevalence of metaphors in certain disciplines (9).

            On the other hand, the use of metaphorical language in molecular
biology--with its references to information, signaling, translation,
editing, etc.--has contributed substantially to its breathtaking success
during the past 50 years. These literary metaphors make extremely
complicated molecular processes intelligible by highlighting their
functional components in a human, or rather semiotic, reference frame. In
this case, metaphors have helped to drive science to new insights.

            As the example of molecular biology suggests, there is a
correlation between the complexity of the phenomena and our dependency on
metaphorical language. It is therefore not at all surprising that metaphors
are ubiquitous in ecology. After all, ecological processes are complex on
any number of scales (time and space, interdependence of large number of
variables, sensitivity to initial conditions, etc.). When he coined the term
"ecology," Ernst Haeckel self-consciously exploited the metaphorical
currency of its Greek roots, oikos and logos, in defining ecology as the
science of the household of nature.

            For Haeckel, ecology was part of the physiological sciences, and
the metaphor of the household of nature was well suited to capture the many
interactions between organisms and their environments. Subsequently, many if
not most ecological concepts reflected familiar cultural experience. Terms
such as alien, assembly, cascade, colonize, community, competition,
consumption, contest, defense, disturbance, efficiency, enemy, equilibrium,
flow, founder, gradient, hierarchy, interaction, invasive, native, niche,
node, productivity, sink, source, stability, succession, territory, web are
all commonly used to define and communicate ecological ideas among
specialists. They have gained at least tacit acceptance by authors,
reviewers, editors, and readers of the scientific literature, who no longer
question their metaphorical origins, but interpret them in the context of
scientific theory.

            Metaphors allow us to build on our experience when we extend
familiar relationships to unfamiliar contexts, and help us to communicate
new ideas to others who share our experiences and are therefore able to
interpret the metaphors. In science, much that we consider knowable is
inferred rather than directly observed. As a result, access to adequate
metaphors can make the difference between comprehension and confusion.
Familiar as they are from common contexts and experiences, most such
metaphors can readily be employed to communicate ecology to nonspecialists.
But ready recognition also carries a cost. The contexts from which terms are
borrowed are not static; the interpretation of specific terms will vary and
evolve. Therefore, common metaphors adopted to carry specialized meanings
can lead us astray; they can constrain understanding as easily as they
facilitate it, and may do both simultaneously.

            Our opening example of "dangerous alien invaders" is an example
of the widespread use of the "natural enemy" metaphor in the ecological
literature. Online, full-text searches of Science and Nature alone have
turned up 54 items that used the term since January 1997. These papers,
mostly research-based reports, are all about ecological topics and have
undergone rigorous scientific and editorial review. Further searches and
analysis confirmed that they are representative of larger trends in the
ecological literature.

            Two-thirds (36) of the papers in Science and Nature included
either an explicit or implied definition or clarification of the term. Of
those 36 studies, 23 provided the clarification after "natural enemy" (or
enemies) appeared in the text. The remaining 18 articles did not define or
clarify their use of the term natural enemy (-ies), apparently concluding
that its meaning was self-evident.

            Throughout the ecological literature, natural enemies refers to
relationships that can be more precisely described as herbivory, predation,
parasitism, parasitoidy, or pathogen infection. Therefore, it is hard to see
what the persistent use of the term natural enemies technically contributes
to any ecological discussion. The popularity of the metaphor with ecologists
thus suggests that the image carries a particular rhetorical power, that it
helps in "getting the message across."

            In the case of the northern snakeheads, the use of the metaphor
was clearly successful in alerting the public to a perceived threat.
However, a less passionate analysis of the case reveals a more equivocal
scenario. Northern snakeheads are Perciformes from a 26-member Old-World
genus. In neutral ecological terms, Channa argus is comparable to the North
American bowfin, Amia calva, a relic of the Triassic order Amiiformes that
is still present in Maryland. Both are about the same size and shape, with
"air-breathing" adaptations to low-oxygen waters; they share appetites for a
broad array of prey, and both have been described as being able to "bite
another fish in half" (10, 11). In many ways, they are a compelling example
of convergent evolution.

            As a result of that convergence, species that survive
cohabitation with bowfins may well survive in the presence snakeheads, and
vice-versa. When discovered 2 years after their release, the snakeheads were
not alone in their Maryland pond. Although a detailed inventory was not
released, the two-step application of herbicides and rotenone, intended to
kill all the snakeheads (and everything else in the pond), revealed the
presence of a variety of organisms, including "thousands of fish." In the
end, a simplified pond was the solution to a simplified problem.

            We are not saying that the presence of the snakeheads could not
have dramatically altered the ecology of freshwater ponds, nor that the
public need not be informed about the large-scale changes in the
distribution of many species as a result of human action (including the
purposeful or inadvertent movement of animals, plants, and microorganisms,
as well as changes in global climate, habitat alteration, etc). But we are
concerned about the implications of the frequent use of bellicose metaphors
such as natural enemies in the ecological literature. The use of the term
natural enemies to describe several different ecological interactions
implies that such a category objectively exists in nature. This assumption
can have serious consequences not only for the snakeheads, but also for the
ability of scientists to comprehend ecological phenomena and for a society
that looks to science for an objective interpretation of the natural world.

            "Enemy" is fundamentally a human construct identifying a
malevolent foe. In our current cultural context, "natural" has a strong
positive value. This can be seen in the ecological literature where the lack
of natural enemies is portrayed as a negative condition. Without natural
enemies, an "invasive" species has an "unfair advantage" (12); released from
a natural enemy, a once naturally constrained species may become a "pest."
In both cases, the metaphor is interpreted as normative.

            In scientific or experimental contexts, dichotomies such as
predator and prey or parasite and host can help us to understand specific
processes in nature. But scientists are (or should be) aware that these are
idealized abstractions. Such idealizations are not restricted to ecology. In
molecular biology, for instance, multiple concepts of the gene refer to a
variety of relationships between DNA "coding" and development. Given the
intricacies of RNA editing, complex regulatory networks, genetic redundancy,
and molecular pathways, it is meaningless to identify any one concrete
natural object as the gene. Yet the existence of such a concrete object is
the prevailing notion shared by a large public and professional community
and is reinforced by the metaphorical language of scientists.

            What troubles us is that biology's metaphorical abstractions all
too easily become concrete objects and substitute for specific, describable
processes. Maximal diversity becomes evolution's telos instead of its
tendency. Biogeographical frontiers become prescriptive and enforceable,
rather than descriptive and conceptual. Seasonal "disturbances" such as
floods interrupt normal ecological processes, instead of exemplifying them.
Biological "productivity" and "diversity" become not only measurable, but
virtuous.

            Perhaps we cannot avoid metaphors altogether in scientific
language. But scientists must be aware of the potential problems inherent in
invoking the familiar as a convenient way for describing their ideas. At the
very least, we should be concerned about what the frequent use of "natural
enemies" (and the notable absence of "natural allies," describing an equally
familiar set of ecological interactions) reveals about the ways in which we
interpret nature through metaphorical lenses, especially in the current
historical situation.

            References and Notes


              1.. A. Huslin, Washington Post, 27 June 2002, p. B3.
              2.. "Anglers on line to tackle invading snakeheads," News in
Brief, Nature 418, 267 (2002).
              3.. "The cartography of life," Netwatch, Science 297, 2175
(2002).
              4.. G. Lakoff, M. Johnson, Metaphors We Live By (Univ. of
Chicago Press, Chicago, 1980)
              5.. D. J. Kevles, In the Name of Eugenics (Knopf, New York,
1985).
              6.. D. Paul, Controlling Human Heredity (Humanities Press,
Atlantic Highlands, NJ, 1995).
              7.. P. Weindling, Health, Race and German Politics Between
National Unification and Nazism, 1870-1945 (Cambridge Univ. Press,
Cambridge, 1989).
              8.. ?. Baumer, NS-Biologie (Hirzel, Stuttgart, 1990)
              9.. R. C. Lewontin, S. Rose, L. J. Kamin, Not in Our Genes:
Biology, Ideology, and Human Nature (Pantheon, New York, 1984)
              10.. Hornaday's American Natural History, 16th ed. (Scribner,
New York, 1935).
              11.. "Snakehead fish in 7 States, U.S. to ban them," Reuters
news release, 23 July 2002.
              12.. U.S. Geological Survey, news release iso-8859-1, 6
February 2003.
              13.. See www.fcsc.usgs.gov/pics/snakehead/snakehead.html

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            The authors are in the School of Life Sciences of the Biology
and Society Program, Arizona State University, Tempe, AZ 85287, USA.
            *To whom correspondence should be addressed. E-mail:
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              Writing for Science - Education
              D.F. McKeen
              SCIENCE Online, 21 Jul 2003 [Full text]

            Volume 301, Number 5629, Issue of 4 Jul 2003, pp. 52-53.
            Copyright ? 2003 by The American Association for the Advancement
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