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■ Macroscope
Evolution’s Other Narrative
Why science would benefit from a symbiosis-driven history of speciation.
Bradford Harris
D
uring a recent meal with a
friend who happens to be a
successful engineer, I found
myself drawn, as usual,
into debate. Although our theological and political views diverge, he and
I customarily find common ground
in scientific epistemology. However,
this time the topic was whether intelligent design should be taught in high
schools. When I expressed incredulity at his support for teaching intelligent design, he said, “Brad, just look
around us—survival of the fittest can’t
be all that’s going on here, and I think
it is important to respect people’s sensitivity to that.”
I reminded my friend that, because
intelligent design argues for supernatural causes of natural phenomena,
teaching it would undermine rational
inquiry, together with students’ ability
to eventually make the kind of scientific
breakthroughs we are enjoying today. I
pointed out the U.S. National Institutes
of Health’s Human Microbiome Project
as an example, which is revealing how
human health suffers when the health
of the millions of microorganisms with
which we’ve coevolved suffers. My
friend’s simplistic interpretation of evolution as “survival of the fittest” left
him ignorant even of the possibility of
projects like this, which are based on
evolutionary considerations of symbiosis. Evidently, educators—and certainly
evolutionary specialists themselves—
must broadcast a more nuanced story
of evolutionary theory. Otherwise, future scientists and projects that inform
better approaches to human health and
global ecology will be sabotaged before
they even emerge.
Bradford Harris is a Ph.D. candidate at Stanford
University in the history of science and technology. Address: 450 Serra Mall, Building 200, Stanford, CA 94305. Email: [email protected].
410
American Scientist, Volume 101
Science education has failed to overcome entrenched cultural ideals rooted
not only in religion, but also in political philosophy. For those like my engineer friend trying to comprehend how
magnificent structures of life emerge
by means of “survival of the fittest,”
skepticism is understandable. Popular
appreciation for life’s complexity has
far outpaced the popular interpretation of the evolutionary source of that
complexity, which has remained stuck
in 1864, when Herbert Spencer coined
the phrase “survival of the fittest.”
When it comes to the story of evolutionary science, people know the name
Charles Darwin, but most do not know
the names Ivan Wallin or Lynn Margulis—two more recent, groundbreaking
evolutionary theorists. Over the past
several decades, these and other researchers have revealed that organisms’
cooperation and interdependence contribute more to evolution than competition. Symbiogenesis—the emergence of
a new species through the evolutionary interdependence of two or more
species—is at least as important in the
history of life as survival of the fittest.
Such insight has failed to gain traction
in American minds—including those
of American scientists—because of cultural history traceable back through the
popularization of Adam Smith’s individualist philosophy.
Darwinism and Individualism
By the time Darwin published On
the Origin of Species in 1859, the Western European and American mind
had long been intellectually primed
to interpret complexity by reducing
perspective to the individual. Adam
Smith’s publication of The Wealth of
Nations 83 years earlier had set the
tone of philosophical and scientific approaches to understanding complex
systems. Fundamental to Smith’s phi-
losophy, as economic historian Warren Samuel reminds us, was the notion that large organizations like the
economy were to be “comprehended
in terms of self-interest or maximization of personal well being.” Smith’s
influence on Darwin was as strong as
it was on the rest of the reading public.
The appeal of this philosophy was
twofold: It morally liberated people to
be selfish, and it intellectually liberated
them to interpret a range of complicated questions in terms of simpler individual parts. When Darwin presented
his theory of evolution in 1859, he stood
firmly on the platform of Smith’s individualist philosophy. As the renowned
evolutionary biologist Stephen Jay
Gould surmised, the essential “Darwinian theory advocates no higher
principle beyond individuals pursuing
their own self-interest . . . [for] Darwin
grafted Adam Smith upon nature to establish his theory of natural selection.”
If mid-19th-century readers struggled
with the unseen mechanism of evolution, then they could do as Darwin did
and conveniently borrow Smith’s economic concept of the “invisible hand.”
For most naturalists and laypeople
alike, the logical extension self-interest
was endless combat. In the second half
of the 19th century, compelling historical reasons existed for this vision. Since
Thomas Hobbes published Leviathan
in 1651, Western Europeans and later
Americans had struggled to reconcile
ideals of self-government with social
stability, often violently. Humanity’s social institutions might separate it from
the violent chaos of nature, but nature’s
violent chaos was assumed. The theory
of natural selection grew out of and reinforced this assumption, and the most
successful circulating English phrases
to distill Darwin’s tome depicted violence, not harmony. Nature was understood, through Alfred Lord Tennyson,
© 2013 Sigma Xi, The Scientific Research Society. Reproduction
with permission only. Contact [email protected].
Endosymbiosis: Homage to Lynn Margulis, a painting by Shoshanah Dubineer, occupies a
hallway in the Morrill Science Center at the University of Massachusetts, Amherst, where
Margulis was a professor until her death in 2011. Margulis maintained that genetic variation
emerges primarily through symbiosis, not through competition, a once-controversial view that
is gaining increasing acceptance. (Image courtesy of the artist, http://www.cybermuse.com.)
as “red in tooth and claw.” Similarly,
T. H. Huxley tapped the psychological
nerve well when he portrayed the history of life as “a continual free fight…
the Hobbesian war of each against all.”
The English political theorist Herbert
Spencer best captured the concept
when he defined natural selection as
“survival of the fittest.”
Simple and cleanly fused with the
entrenched political ideal of individualism, Darwinian natural selection
totally dominated the Western perspective on evolution for more than a
century. But even before the end of the
19th century, some Western naturalists began interpreting evolutionary
principles differently, looking beyond
competition to the role of cooperation.
These investigators studied the
many “individual” species that resembled a composition of autonomous species or specie parts somehow working
in association—for example, lichens,
giant green anemones, and termites.
In the 1880s, for example, the Scottish
www.americanscientist.org
biologist Patrick Geddes interpreted
the biological relationship between the
algal and animal cells in giant green
anemones as a special form of speciation. He reasoned that green algal cells
were infused into the animal flesh of
the anemone cooperatively. Geddes’s
chief interest was the evolution of this
relationship. In 1882 he published in
Nature under the title “Symbiosis of
Alga and Animals,” in which he argued that the giant green anemone,
which outnumbered competing anemones that lacked algal cells, represented
evolutionary adaptation outside the
conceptual framework of Darwinism.
Geddes was not the first to use the
term symbiosis, but he was among the
first to discuss it in terms of evolution.
He appreciated that symbiotic associations between “species” could become so integral to their biology that
their individual species identity had
little meaning outside of the relationship. Although admired briefly by his
cohort, however, “Symbiosis of Alga
and Animals” was buried beneath his
work in other disciplines, such as urban planning. Apparently constrained
by his culture’s prevailing individualist perspective, Geddes never fully articulated a theory of symbiotic-driven
speciation, nor did any other Western
European or American scientists for
another two generations.
If an evolutionary theory featuring symbiotic-driven speciation was
to emerge, then it would likely do so
outside Western Europe and North
America. In fact, by 1910 Russian biologists had raced ahead with the idea
of symbiotic-driven speciation. In that
year enough relevant evidence had
accumulated in the Russian scientific
community for the botanist Constantin
Merezhkowsky to create a new evolutionary term: symbiogenesis. He declared
that the term aptly described “the origin
of organisms by the combination or by
the association of two or several beings
which enter into symbiosis.”
The Russians were not merely unswayed by the Western European and
American cultural ideal of individualism; many of them were explicitly
hostile to it. The well-known Russian
naturalist, evolutionary theorist, and
political philosopher Peter Kropotkin
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2013
November–December
411
was highly critical, especially
of Huxley’s “Hobbesian war of
each against all.” In his travels
across Siberia, Kropotkin was
impressed by the cooperation
he observed among people and
animals. Saddled with his own
cultural biases tilting toward
socialism, Kropotkin was most
interested in how the intra- and
interspecies relationships of
people, reindeer, birds, fish, ants,
and numerous other organisms
enabled them to survive the
harsh Siberian winters.
Outside of their ecological associations, Kropotkin believed,
individual organisms were not
worth studying from an evolutionary perspective, because
isolated individuals were not
biologically viable in the unforgiving Siberian environment. In
his most popular work, Mutual
Aid (1902), Kropotkin wrote that
“mutual aid is as much a law of animal life as mutual struggle, but . . . as
a factor of evolution, it most probably
has a far greater importance.” He explained that “it favors the development
of such habits and characters as insure
the maintenance and further development of the species.”
According to science historian Liya
Nikolaevna Khakhina, Russian evolutionary theorists did not discount Darwinian natural selection, but they did
conceive of it differently. By the 1920s,
many Russian scientists had come to
believe that “symbiosis was the source
of evolutionary novelty but natural
selection . . . acted on emerging and
tightening symbiotic associations.” In
other words, according to Khakhina’s
notion of speciation, if “symbiosis is the
author, natural selection is the editor.”
The Story of Symbiogenesis
Throughout the first half of the 20th
century in Western Europe and America, even as scientists reduced their
investigations on evolution down to
the microscopic level of the cell, the
individualist school of thought continued to dominate. Researchers assumed that the genes inside the cell
nucleus contained all the information
determining an individual’s functions,
traits, and health, and therefore the
individual’s evolutionary prospects.
The new preoccupation with genetic
competition only extended the appeal
of interpreting evolution as survival
412
American Scientist, Volume 101
H
ER
The protozoan Euplotidium is a marine
ciliate that carryies bacterial ectosymbionts
called epixenosomes. These bacteria protect
their host from predators by extruding a ribbon-like apparatus (right) that functions like
a crossbow. (Protozoa image is courtesy of
Giovanna Rosati; epixenosome image from
Petroni Giulio, Proceedings of the National
Academy of Sciences 97:1813–1817.)
of the fittest. Nonetheless, struggling
against this reinforced structure, a minority of investigators maintained interest in symbiotic interpretations of
biological adaptation. For these scientists, nuclear genetics told only part of
the evolutionary story.
One of the most important of these
symbiotic thinkers was Ivan Wallin of
the University of Colorado, Boulder.
During the 1920s he set out to investigate the history of the eukaryotic cell
organelles called mitochondria—the
globular structures outside the nucleus that produce the cell’s energy.
Wallin proposed a radical hypothesis:
Mitochondria did not evolve endogenously through a long history of random nuclear genetic mutation; instead,
mitochondrial organelles inside our
cells descended from bacteria that had
formed cooperative associations with
our cells—with us. This idea contradicted combative survival of the fittest.
In 1927 Wallin published Symbionticism and the Origin of Species, in which
he pointed out that mitochondria’s
possession of their own, distinct genes
showed their independent bacterial ancestry. This was the first
direct genetic evidence presented to the western European and
American scientific community
that supported the theory of
symbiogenetic evolution.
Wallin should have caused a
sensation, but Western scientists
failed to take note. Symbiogenetic
insights remained overshadowed
by the preoccupation with cell
nuclei. Especially after the resurrection of Gregor Mendel’s work,
most scientists believed that any
genetic material that might be
found outside the cell nucleus
was unimportant to evolution.
The public, meanwhile, was
less interested in esoteric variations in evolutionary theory
among experts than they were
with the creationism-evolution
debate during the 1925 State of
Tennessee v. Scopes trial. Whether evolution was real—not how it
proceeded—was the popular drama.
When Scopes was a fading memory in
the 1950s, James Watson’s and Francis
Crick’s revelation of the double-helical
structure of DNA subsumed symbiogenesis under a whole new generation
of enthusiasm for nuclear genetics. Yet
another generation passed before the
evolutionary biologist Lynn Margulis
succeeded in revivifying the insights of
Wallin and the earlier Russian symbiogeneticists.
Lynn Margulis’s Legacy
According to Margulis, the evolving
relationships between microscopic organisms and other micro- and macroscopic organisms are the essence of
the history of life. Despite scientists’
mid-century focus on eukaryotic life
(organisms with larger cells featuring
a bounded nucleus and organelles),
the most prolific type of organism on
Earth, bacteria, is prokaryotic (an organism without a bounded nucleus).
Virtually all eukaryotic forms of life
have adapted symbiotic associations
with prokaryotic bacteria. Margulis
was among the first Western scientists
to attempt to popularize this fact. She
spent virtually her entire career laboring to bring this mostly microscopic
form of evolution to the macroscopic
focus of her readers.
Margulis’s research in microbiology
equipped her to verify and expand on
Wallin’s symbiosis-centered theory. In
© 2013 Sigma Xi, The Scientific Research Society. Reproduction
with permission only. Contact [email protected].
1966 she attempted to publish a summary of her perspectives on the evolution of complex life forms in “The Origin of Mitosing Eukaryotic Cells,” only
to be rejected by more than a dozen scientific journals. When her article was
finally published by the Journal of Theoretical Biology, criticism ensued. Nonetheless, the further Margulis pushed
her symbiotic evolutionary theory, the
more convinced she became that the
emergence of eukaryotic cells a billion
and a half years ago—a major evolutionary transition in the history of
life—was the result of symbiogenesis.
In Margulis’s view, out of prokaryotic–
prokaryotic symbiosis emerged eukaryotes. Out of prokaryotic–eukaryotic
symbiosis emerged more competitive
eukaryotes. And out of eukaryotic–eukaryotic symbiosis emerged multicellular life. The classic image of evolution,
the tree of life, almost always exclusively shows diverging branches; however,
a banyan tree, with diverging and converging branches is best. To this day,
many scientists and most laypeople remain ignorant of this way of imagining
evolution, which profoundly constricts
how they imagine themselves.
Most of the mass of our DNA is
“ours” because there are many more
cells making up our body than there
are composing the microorganisms living in and on our body. Nonetheless,
most of the genetic diversity in and on
our body is not ours. Rather, it is found
in the microscopic organisms with
which our body interacts to maintain
optimal health. Eyelash mites, skin
fungi, gut bacteria, and more all work
in harmony with us. “Each one of us is
a massive colony of microorganisms,”
Margulis explained. “Former protists
are now eloquently orchestrated animals with fancy tissues and organs.”
Some of Margulis’s most vivid contributions to a richer understanding of
evolution appear in her books Symbiotic
Planet: A New Look at Evolution (1999)
and Acquiring Genomes: A Theory of the
Origins of Species (2002). In Acquiring Genomes Margulis describes, for example,
the evolutionary integration of genetically distinct bacteria onto the surface
of a genus of ciliated saltwater microorganisms called Euplotidium. All six species of Euplotidium bear surface bacteria
that act like archers defending the royal
Euplotidium castle. When Euplotidium
species sense approaching predators,
their surface bacteria react by shooting
out ribbons of protein, like little micronwww.americanscientist.org
sized crossbows. The ciliated Euplotidium cannot survive without these protective bacteria, nor do these particular
extracellular bacterial organelles appear
to exist anywhere except on the surface
of the six known Euplotidium species.
Laboratory experiments to cultivate
these bacteria removed from Euplotidium have failed; without the association
between the two entities, neither could
exist. The association that evolved between the ancestors of Euplotidium and
Some of the
potentially most
therapeutic
applications of
symbiogenetic
science today are
being directed
toward problems of
chronic disease.
its surface bacteria catalyzed the origin
of this genus. This kind of symbiogenetic speciation typifies the role that
prokaryotes play in the evolutionary
history of eukaryotic life. Wherever biologists now look in nature, they find
examples of unicellular and multicellular eukaryotes that exist in association with bacteria and algae possessing
distinct genomes.
Despite Margulis’s legacy, early 20thcentury concepts of “survival of the fittest” continue to determine how evolution is taught and, therefore, how it is
understood even by most scientists. Beyond the popular discourse, relatively
advanced textbooks devoted entirely to
the study of evolution omit the concept
of symbiogenesis. The fourth edition of
a leading undergraduate textbook of
evolution, Evolutionary Analysis (2008),
still devotes entire sections to “combat,” “competition,” and “conflict,” neglecting symbiosis. Most high school
graduates are taught the term symbiosis,
but it is typically presented to mean
little more than mutually beneficial
cooperation. Students learn how symbiosis benefits individuals, but not how
symbiotic relationships themselves often constitute emergent organisms that
display their own evolutionary histories. Only evolutionary specialists have
universally adopted an appreciation for
symbiogenesis.
Recovering the story of evolution
goes a long way toward understanding how to maintain the integrity of a
living organism. Wherever symbiotic
ideas spread, they lead to important
new practical insights. Some of the
potentially most therapeutic applications of symbiogenetic science today
are being directed toward problems
of chronic disease. Many medical scientists are drawing inspiration from
Margulis’s and others’ symbiogenetic
research to reorient approaches to human health, as it becomes clearer that
microbes that have evolved symbiotically with humans are integral to our
well-being. The dramatic rise in rates
of allergies, eczema, ulcerative colitis,
and other chronic health problems are
increasingly believed to involve a perturbation in the human–microbe relationship, leading in 2008 to the Human
Microbiome Project.
Exploring the history of scientists’ attempts to understand evolution reveals
neglected insights into the associations
between individuals, associations at
least as meaningful as the individuals
themselves. Now, thanks to Margulis,
these insights are finally beginning to
percolate from the realm of the lone
expert to that of the wider scientific
community, the classroom, and even
the dinner table. Supporting this trend
will benefit our stewardship of human
and global ecology. As we disentangle
some of our political discursive traditions from our scientific ones, the story
of evolution may itself evolve.
Bibliography
Huxley, T. H. 1888. The struggle for existence in human society. Nineteenth Century
23:195–236.
Khakhina, L. N. 1992. Concepts of Symbiogenesis: A Historical and Critical Study of the Research of Russian Botanists. New Haven, CT:
Yale University Press.
Kropotkin, P. 1904. Mutual Aid: A Factor of
Evolution. Reprint. Hong Kong: Forgotten
Books.
Margulis, L. 2002. Acquiring Genomes: A Theory
of the Origins of Species. New York: Basic
Books.
Sapp, J. 2002. Symbiogenesis: The hidden face
of Constantin Merezhkowsky. History and
Philosophy of the Life Sciences 24:413–440.
© 2013 Sigma Xi, The Scientific Research Society. Reproduction
with permission only. Contact [email protected].
2013
November–December
413