become harder to define when they extend
their metabolisms through, and become dependent upon, one another.
are also clearly metabolically integrated. The products of photosynthesis
flow from bluegreen or green to the translucent partner. What is
seldom realized is that in tight associations the metabolites flow
in both directions. The animal or fungal partner also releases materials
to the photosynthesizer. Symbioses are two-way exchanges. The kindness
of strangers, the metabolic flow of gifts, makes them less strange
and, ultimately, part of a single, co-dependent biological self."
the lower we go in the scale of being, the more necessary is geographical
unity for that close interaction of individuals which constitutes
society. Societies of the higher animals, of insects, of molecules,
all possess geographical unity. A rock is nothing else than a society
of molecules, indulging in every species of activity open to molecules.
I draw attention to this lowly form of society in order to dispel
the notion that social life is a peculiarity of the higher organisms.
The contrary is the case. So far as survival value is concerned,
a piece of rock, with its past history of some eight hundred millions
of years, far outstrips the short span attained by any nation."
A mutually beneficial relationship among organisms is called symbiosis.
The concept of symbiosis can blur the distinction
between organisms and their environments. For example, if a plant
requires the participation of an organism of a different type, a bee,
say, to reproduce, then the bee is a part of the plant’s reproductive
cycle. And if the bee requires the pollen from the plant to feed its
larvae, then the plant participates in the bee’s reproductive cycle, and the organisms enjoy a symbiosis.
The organism is the beeplant. To where the bee flies, the plant might
extend its range. To where the plant’s seeds light, perhaps due
to the intervention of a bird, a new beehive might be established.
(And the bird adds its own layer of complication.) Symbiotic
organisms extend one another's metabolisms.
A lichen appears to be a single type of organism, but lichens are
integrated symbiotic communities of bacteria and fungi.
A micro-organism that lives in the gut of the termite is another example of symbiosis. It produces an enzyme that enables the termite to digest cellulose (wood fiber).
The human body by cell count consists mostly of symbiotic bacteria—about 90 percent of a human body’s cells are bacterial. Although this population of microbes, the human microbiome is a topic of ongoing research, its dynamics have been mapped sufficiently to expose the hjuman body as a complex ecosystem.
The figure at left shows the human body and its many microbial communities. (Illustration by Patricia J. Wynne, from Welcome to the Microbiome, by Rob DeSalle and Susan L. Perkins, Yale University Press, 2015.) The authors observe,
“[P]erhaps as many as 90 percent of the cells in a typical healthy human body are microbes, and that up to 3 percent of our body mass is made of microbial interlopers. [. . . .] As unbelievable as it may seem, our genomes have evolved to cope with and even cooperage with these microbial residents.”
Moreover, this population of micro-organisms evolves by ecological succession. Summarizing a study of the effects of handwashing on bacterial communities that live on human skin, the same authors note that, surprisingly,
“[I]t turns out that time since last handwashing was not correlated with diversity [of microbes on the skin] and, in fact, the degree of diversity is pretty much the same regardless of time since washing. What did change over time were the kinds of bacteria found on the hand since the last washing, implying that there is a kind of succession of bacteria that colonize a clean hand. Certain types of bacteria jump on at first and establish themselves, and then a little later others take over.”
Bodies of complex organisms are themselves ecosystems that host rotations of symbiotic populations and otherwise display the same dynamics as characterize macro-ecosystems.
Furthermore, researcher Anna Skalka, Director
Emeritus, Institute for Cancer Research, Fox Chase Cancer Center, and
colleagues estimate that at least 8 percent of the human genome is of
viral origin. She is interviewed about the work on National Public Radio HERE.
Symbiosis raises the question: When organisms cooperate for mutual benefit, whose metabolism is whose?
ambiguities encountered when trying to distinguish organisms from one another is a
problem for evolution theory, because the theory needs to define
something discrete for nature to "select" from among her interwoven
metabolic processes. Which is a discrete unit of evolutionary selection,
a gene, a trait, an individual organism, a species? This "granularity
problem" plagues the Darwinian model.
take a dramatic turn in the case of endosymbiosis.
This occurs when varieties of unicellular organisms merge
to form a new kind of cell, which, being a conglomerate of symbionts,
has a structure more complex than any of its formerly independent constituents.
According to normal evolution theory, various species of bacteria, or
prokaryotes, merged to create the more complex, eukaryotic, cells that
make up the bodies of multicellular plants and animals. The notion that
this is how complex cells arose, through a communal pooling of resources
on the part of bacteria, was greeted with scorn when researcher Lynn Margulis
proposed the idea in the 1960s. But she got the last laugh. Endosymbiosis
is accepted today by most evolutionary theorists as the most plausible
path to eukaryotic cells.
one must always ask how the partners are integrated, if they
are always integrated, and what environmental conditions influence their
integration. To substitute these sorts of details of metabolite flow
and gene-product transfer between intimate former strangers with neodarwinian
terms like 'cooperation', 'cost',' or 'benefit' is absurd and exemplary
of the fallacy of misplaced concreteness. Such terminology precludes
real understanding of the inevitably rich and complex evolutionary
past of the symbiotic world that made animals, plants, and
their nucleated planetmates."
coupled anabolic and catabolic subprocesses create the illusion that bodies
are fundamentally discrete biological units, with tthe metabolic process per se being the dynamic structuring pattern. But organism
is a conceptual convenience that designates a relatively stable cross-section
of overlapping, interdependent metabolisms. Organisms make their ways among
other organisms, making and breaking bonds of various kinds, forming new
entities in their combinations and recombinations of metabolic interveavings.
Humankind's Extended Symbiont
Is the coral
of the reef distinct from, or part of, the living polyp
that excretes the coral? Is the coral an artifact of polyp technology,
a component of the polyp's physical environment, or the true
skin of the polyp body? Can the reef's coral be part of the organism and itself
not be living? If so, it suggests that an organism can have two parts,
one possessed of livingness and one not, the two being interwoven in the body
of the thing. But are the molecules themselves possessed of livingness?
Are the iron atoms that ride along in the hemoglobin molecule that keeps
humans alive, alive?
The concept of symbiosis can be abstracted
to include social behaviors, as forms of intraspecific symbiosis. Microbiologist Bonnie Bassler describes symbiotic/social
behaviors among bacteria and the chemical signaling involved to keep their societies thriving.
as intuitively nonliving as atoms of iron turn out to be essential
to the lives of certain organisms, but it seems doubtful
that any iron atom distinguishes between participating in living
processes and nonliving ones. During its lifetime an iron atom will
make and break bonds with countless other atoms, in iron ore, hemoglobin molecules
and rusty nails. Nature's matter and energy exchanges crisscross
seamlessly between the organic and the inorganic. Nature
seems uninterested in maintaining walls of separation between the two
domains. This observation raises questions
about the character of manufactured (organic and inorganic) artifacts
and humankind's relationships with them.
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