Wednesday, November 21, 2012

Charles Mann Ponders The State Of The Species


Charles Mann ponders the age-old question of whether humans are smarter than yeast:
As a student at the University of Moscow in the 1920s, Georgii Gause spent years trying—and failing—to drum up support from the Rockefeller Foundation, then the most prominent funding source for non-American scientists who wished to work in the United States. Hoping to dazzle the foundation, Gause decided to perform some nifty experiments and describe the results in his grant application.

By today’s standards, his methodology was simplicity itself. Gause placed half a gram of oatmeal in one hundred cubic centimeters of water, boiled the results for ten minutes to create a broth, strained the liquid portion of the broth into a container, diluted the mixture by adding water, and then decanted the contents into small, flat-bottomed test tubes. Into each he dripped five Paramecium caudatum or Stylonychia mytilus, both single-celled protozoans, one species per tube. Each of Gause’s test tubes was a pocket ecosystem, a food web with a single node. He stored the tubes in warm places for a week and observed the results. He set down his conclusions in a 163-page book, The Struggle for Existence, published in 1934.

Today The Struggle for Existence is recognized as a scientific landmark, one of the first successful marriages of theory and experiment in ecology. But the book was not enough to get Gause a fellowship; the Rockefeller Foundation turned down the twenty-four-year-old Soviet student as insufficiently eminent. Gause could not visit the United States for another twenty years, by which time he had indeed become eminent, but as an antibiotics researcher.

What Gause saw in his test tubes is often depicted in a graph, time on the horizontal axis, the number of protozoa on the vertical. The line on the graph is a distorted bell curve, with its left side twisted and stretched into a kind of flattened S. At first the number of protozoans grows slowly, and the graph line slowly ascends to the right. But then the line hits an inflection point, and suddenly rockets upward—a frenzy of exponential growth. The mad rise continues until the organism begins to run out of food, at which point there is a second inflection point, and the growth curve levels off again as bacteria begin to die. Eventually the line descends, and the population falls toward zero.

Years ago I watched Lynn Margulis, one of Gause’s successors, demonstrate these conclusions to a class at the University of Massachusetts with a time-lapse video of Proteus vulgaris, a bacterium that lives in the gastrointestinal tract. To humans, she said, P. vulgaris is mainly notable as a cause of urinary-tract infections. Left alone, it divides about every fifteen minutes. Margulis switched on the projector. Onscreen was a small, wobbly bubble—P. vulgaris—in a shallow, circular glass container: a petri dish. The class gasped. The cells in the time-lapse video seemed to shiver and boil, doubling in number every few seconds, colonies exploding out until the mass of bacteria filled the screen. In just thirty-six hours, she said, this single bacterium could cover the entire planet in a foot-deep layer of single-celled ooze. Twelve hours after that, it would create a living ball of bacteria the size of the earth.

Such a calamity never happens, because competing organisms and lack of resources prevent the overwhelming majority of P. vulgaris from reproducing. This, Margulis said, is natural selection, Darwin’s great insight. All living creatures have the same purpose: to make more of themselves, ensuring their biological future by the only means available. Natural selection stands in the way of this goal. It prunes back almost all species, restricting their numbers and confining their range. In the human body, P. vulgaris is checked by the size of its habitat (portions of the human gut), the limits to its supply of nourishment (food proteins), and other, competing organisms. Thus constrained, its population remains roughly steady.

In the petri dish, by contrast, competition is absent; nutrients and habitat seem limitless, at least at first. The bacterium hits the first inflection point and rockets up the left side of the curve, swamping the petri dish in a reproductive frenzy. But then its colonies slam into the second inflection point: the edge of the dish. When the dish’s nutrient supply is exhausted, P. vulgaris experiences a miniapocalypse.

By luck or superior adaptation, a few species manage to escape their limits, at least for a while. Nature’s success stories, they are like Gause’s protozoans; the world is their petri dish. Their populations grow exponentially; they take over large areas, overwhelming their environment as if no force opposed them. Then they annihilate themselves, drowning in their own wastes or starving from lack of food.

To someone like Margulis, Homo sapiens looks like one of these briefly fortunate species.
The whole thing is here:  State of the Species: Does success spell doom for Homo sapiens? Charles Mann, Orion Magazine. It ends on a cautiously optimistic note, one which I wish would feel more confident in.

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