Cosmic Apprentice: Dispatches from the Edges of Science (21 page)

But the striking likeness between mitochondria and respiring bacteria, on the one hand, and between plastids and photosynthetic bacteria, on the other, has “proved” beyond a reasonable scientific doubt that all cells with nuclei, from a unicellular amoeba to a multibillion-cell anaconda, come from more or less orgiastic encounters (eating, infecting, engulfing, feeding on, having sex with, and so on) among quite different types of bacteria.
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It is now generally agreed, not to mention taught in textbooks, that both mitochondria and chloroplasts derive from bacteria.

Like the chimera, the plant cell recombines three distinct and once-separate entities: protective anaerobic host cell, internally multiplying photosynthetic bacterium, and respiring bacteria. The evolution of these last was sparked by the accumulation of highly combustible originally poisonous free oxygen within the atmosphere of the early Earth. Only anaerobic bacteria dwelled on Earth at this time. The lack of free atmospheric oxygen is attested to, some two billion years ago, by the replacement of banded iron formations (presumed to be the fossil remains of communities of photosynthesizing bacteria) with heaps of rust (representing the accumulation of atmospheric oxygen to near-present concentrations).

The buildup of atmospheric oxygen was itself a cyanobacterial phenomenon, since the metabolic waste product of the mutation, which allowed photosynthetic bacteria to use water as a source of hydrogen, was none other than gaseous oxygen, at first an extremely hazardous waste. Those bacteria that did not evolve to tolerate or use oxygen, or team up with cells that did, died. Although the accumulation within Earth’s atmosphere of oxygen was initially catastrophic, it was also an energetic catalyst for organisms such as the oxygen-respiring ancestors of mitochondria, which employed the new abundance of the highly reactive gas to produce intracellular energy reserves at many times the rate of their fermenting bacterial predecessors.

Modern fermenting bacteria include anaerobes that, like trolls or elves in a cosmic fairy tale, protect themselves from the hazards of surface oxygen by dwelling underground. Vestiges of the anaerobic environment of the early Earth survive as shoreline stromatolites (rounded bacteria-built stones) and their softer relatives, microbial mats.
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Human beings belong to the army of mutants that evolved in the aftermath of the oxygen infusion, the greatest pollution crisis Earth has ever known.

There is less evidence for another player in the symbiotic game whose evolutionary permutations have provided us with all known species of animals and plants: the spirochete. The spirochete’s presence has been postulated to persist in ghostly form in all cells possessing the undulating organelles perhaps best known as undulipodia.
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Undulipodia, whose electron microscopic ultrastructure reveals a characteristic “9+2” tubular form, are common to the cilia of women’s oviducts and the sperm tails of ginkgo trees (and much else besides). My mother believed these undulating organisms derive from a not-yet-discovered species of spirochete. It was a seductive idea: these wriggly beings, so pervasive in oxic and anoxic muds, so prolific and with such a terrific penchant to form partnerships—sometimes attaching as swimming appendages to larger cells—moved in, like a sperm to an egg, but with more distinct consequences. If the ancestors to mitochondria can do it, and slow green beings that don’t need to be taken to dinner, then why not the speeding spirochetes, so prolific in numbers and species, so metabolically versatile and naturally infectious?

Ever-squirming spirochetes fed not only alone but at the periphery and even inside larger cells. Inside cells themselves inside termites they can be seen to synchronize their slippery selves, so prolific is their reproduction in undulating activity in a limited space. In Grand Central Station swarms, these versatile beings, my mother reasoned, would be afforded all manner of opportunities for microbial merger; one possibility, she argued, was that neurological abilities made use of co-opted spirochete infrastructure, gene, and protein complexes, as this most ancient of eukaryote symbioses was redeployed in the neural and sensory apparatus (e.g., the active, microtubular brain) of “higher organisms.”

The edges of larger cells, sites of leakage supplying a constant flow of food, were such prime real estate that some spirochetes appear to have renounced their former freedom of movement in order to permanently attach. Later, serving as a means of locomotion and food acquisition to larger cells, the spirochetes would have become increasingly phantomlike as they evolved ever-more harmoniously into the chimerical eukaryotic system. Today, mitosis and the mitotic spindle may be like the smile of Charles Dodgson’s Cheshire Cat: the faded remnants of a life-form that has all but vanished into symbiotic thin air. In a living environment, parts of the self can be gradually lost. Spirochete remnants, alive and well, haunt the phenome, lying at the deepest, most ancestral levels of our being. Finding evidence for such spirochetes, however, remains a problem.

The human body, too, is an architectonic compilation of millions of agencies of chimerical cells. Each cell in the hands typing this sentence comes from two, maybe three, kinds of bacteria. These cells themselves appear to represent the latter-day result, the fearful symmetry, of microbial communities so consolidated, so tightly organized and histologically orchestrated, that they have been selected together, one for all and all for one, as societies in the shape of organisms.

The wastes of microbial communities, analogous to our garbage dumps and landfills, have also been incorporated as organisms breed together and organismhood appears at spatially more inclusive levels. The mineral infrastructure of our bodies, for example, the calcium phosphate of bone, owes its existence to the necessity of eukaryotic cells to keep cytoplasmic calcium concentrations at levels around one in ten million. Because seawater concentrations of calcium are often four orders of magnitude higher than this, ocean-dwelling cells must exude calcium to avoid poisoning. In the full-fathomed sea did the bones of our ancestors and the shells of their eukaryote relatives evolve. Skeletons dramatize an ancient waste, whispering a ghostly testimony to the useful internalization of hazardous waste sites. This gives a good indication of how life within the general economy evolves to deactivate, sacrifice, and eventually incorporate the dangerous excesses that accrue from its solar growth.
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The implications of a new biology for that identity which arises epigenetically from a single protist-like fertilized egg cell and for the zoocentric, medically proper model are immense. The body can no longer be seen as single, unitary. It is multiple, even if orchestrated by vicissitudes and the need for harmony over evolutionary time. We are all multiple beings. Our chimerical nature is less obvious than
Mixotricha paradoxa,
a species of autonomous nucleated cell (i.e., a protist) that seems to be unicellular but, on closer inspection, is seen to consist of several different kinds of cells—among them internal oxygen-respiring bacteria and externally attached spirochetes that serve as oars. In addition
M. paradoxa
contains its “own” organelles, congenital undulipodia used as rudders that, along with the spirochetes, help propel it through a droplet of water. In the transformation from organism to an organelle, cell membranes meld and, ultimately, disappear, as organisms undergo intraorganismic genetic transfers (an example of bacterial omnisexuality) to become organelles.

The brain’s neurons, rich in the tubulin proteins that form the walls of the cell fibers known as microtubules, may also be the highly modified remnants of intra- and extracellular spirochetal mobility systems.
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Undulipodia all consist of microtubules built of tubulin proteins; some spirochetes contain tubulinlike proteins. If the body–brain is not single but the mixed result of multiple bacterial lineages, then health is less a matter of defending a unity than maintaining an ecology.

Whereas the zoocentric model causally ascribes diseases to organisms, the new biology recognizes that many putative disease agents—such as streptococcus bacteria and
Candida albicans
fungi—are normally present in the human biological system. As we move to a new model, the body becomes a sort of ornately elaborated mosaic of microbes in various states of symbiosis. The distinct presence of these microbes becomes noticeable only when festering and illness throw normal populations and metabolite turnover out of equilibrium. Drugs used to treat bacterial meningitis can kill the bacteria, but in doing so can upset the body’s internal microbial ecology with the result that fungi, usually held in check, proliferate fatally in the cerebrospinal fluid.
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Moreover, disturbances of the body’s normal microbial ecology do not, properly speaking, signal sickness so much as the emergence of difference and novelty. Like cataracts or the glaucomous decay of vision, which may lead an artist into new percepts of flowery fields, so the same
Treponema
spirochete associated with deterioration has been linked with remarkable mental feats and artistic productions—here, for example, by the writer Anthony Burgess:

The body is not one self but a fiction of a self built from a mass of interacting, supervening selves. A body’s capacities are literally the result of what it incorporates; the self is not only corporal but corporate.

GAIA

Just as the technologies of microscopic apparatus have opened the way toward a view of the human organism as a massive microbial ecosystem, in which eukaryotic waste products such as calcium have been honed into the calcium phosphate architecture of the human skeleton, so too have telescopic technologies opened the way toward seeing Earth as a living entity, in which animals are not independent actors but organelle-like components within a functioning planetary physiology. It is the timidity of our view, the ecological cognate of both our existential separation and our lack of understanding, that leads us to underestimate the interconnectivity and complexity organisms cocreate with one another and the substances of the geosphere, atmosphere, and hydrosphere.

Gaia, in its vulgar but succinct version, claims that Earth is alive. Yet, with greater nuance and accuracy, it can be stated that Earth’s largely biogenic surface, the biosphere, appears to regulate itself physiologically within the astronomic medium; it behaves
as
a body. Gaia need not be conscious to act in ways that appear to humans to evince consciousness—even a computer program with complex feedbacks can mimic intelligence, and biospheric biological feedbacks are arguably far richer, the living crucible in which human intelligence evolved. Moreover, Gaia, while alive, differs from an organism because it is a closed ecology, recycling its wastes completely. This basic brutal fact also belies the notion that the Gaia hypothesis represents a fine and happy balance of harmony-optimizing organisms. There is a sense in which Gaia optimizes energy dispersal, but all sort of organisms, species, and larger taxa are disposed of as the biosphere increases its ability to access and make use of energy reserves. Thus those who criticize the notion by suggesting that organisms are exposed to hardships or “eat their own children” do not effectively challenge the notion of a planetary phenomenology that regulates itself in the manner of a body. Indeed, the research program of an environment deeply embedded in material feedbacks has been co-opted by geology and geosciences departments under the name of Earth system sciences, which appropriates James Lovelock’s systems cybernetic approach while distancing itself from perceived new age baggage.

Oxygen accounts for about one-fifth of our atmosphere; the mean temperature of the lower atmosphere is about 22 degrees centigrade and its pH is just over 7. Although the sun’s luminosity is thought to have increased over 30 percent since the first life appeared on the planet and although combustible oxygen instantly reacts with many sorts of molecules nonetheless normally present in the atmosphere (because their concentrations are physiologically replenished), these values (temperature, pH, and the distribution of reactive gases) have remained extraordinarily stable for hundreds of millions of years. A major argument here has to do with free oxygen, which once existed only negligibly in the atmosphere: Yet, far from the increase in oxygen being a counterexample to Gaian regulation, the switch from a relatively languid anaerobic to a higher energized redox planet can also be taken to represent a planetwide metamorphosis, a violent organic homeorrhesis akin to (and in some ways perhaps even formally similar to) developmental changes such as the hormonal floods of puberty or the genetically mediated transformation of a caterpillar. (Unlike reactive machines, proactive living beings return to previous states that themselves are often changing, so-called moving set points; they are often homeorrhetic, meta-stable, or fluidly stable, rather than homeostatic, simply looping back to the same value, like a set temperature on a thermostat.) Unlike animal bodies, the living Earth—qua its proximate resources—is one of a kind and thus is not exposed to natural selection. Nevertheless, the global regulation of geophysical values over evolutionary time may be likened to the regulation of the body temperature of a mammal over decades; this allows one to speak meaningfully of a Gaian “physiology,” of Earth’s surface as being alive.
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