Cycles

46. CYCLES

Everybody knows about the familiar large-scale cycles of nature: day follows night follows day; summer-fall-winter-spring-summer-fall-winter-spring; the water cycle of evaporation and precipitation that refills our lakes, scours our rivers, and restores the water supply of every living thing on the planet. But not everybody appreciates how cycles—at every spatial and temporal scale from the atomic to the astronomic—are quite literally the hidden spinning motors that power all the wonderful phenomena of nature. Nikolaus Otto was working on internal-combustion gasoline engines in 1861, and Rudolf Diesel built his engine in 1897. These engines exploit repeating cycles that accomplish work and return to starting conditions for the next round. Otto’s four-stroke cycle and the cycles used by Diesel engines differ in their details; Diesel engines can use different stroke arrangements. The details of these cycles are ingenious, and they have been discovered and optimized by an R & D cycle of invention that is several centuries old. An even more elegant, microminiaturized engine is the Krebs cycle, which was discovered in 1937 by Hans Krebs, but invented over millions of years of evolution at the dawn of life. It is an eight-step series of chemical reactions that helps cells extract usable energy from fuel and is central to metabolism in many organisms.

Biochemical cycles like the Krebs cycle are responsible for all the motion, growth, self-repair, and reproduction in the living world, wheels within wheels within wheels, a clockwork with trillions of moving parts, and each clock needing to be rewound, restored to step one so that it can do its duty again. All of these cycles have been optimized by the grand Darwinian cycle of reproduction, generation after generation, picking up fortuitous improvements over the eons.

At a completely different scale, our ancestors discovered the efficacy of cycles in one of the great advances of human prehistory: the role of repetition in manufacture. Take a stick and rub it with a stone and almost nothing happens—a few scratches are the only visible sign of change. Bring the stick back to the starting point and do it again. Still you have almost nothing to show for your efforts. Rub it a hundred times and there is still hardly anything to see. But rub it just so, for a few thousand times, and you can turn it into an uncannily straight arrow shaft. By the accumulation of imperceptible increments, the cyclical process creates something altogether new. The combination of foresight and self-control required for such projects was itself a novelty, a vast improvement over the repetitive but largely instinctual and mindless building and shaping processes of other animals. And that novelty was itself a product of the Darwinian cycle, enhanced eventually by the swifter cycle of cultural evolution, in which the reproduction of the technique wasn’t passed on to offspring through the genes but transmitted among non-kin who picked up the trick of imitation.

The first ancestor who polished a stone into a handsomely symmetrical hand axe must have looked pretty stupid in the process. There he sat, rubbing away for hours on end, to no apparent effect. But hidden in the interstices of all the mindless repetition was a process of gradual refinement that was well-nigh invisible to a naked eye designed by evolution to detect changes occurring at a much faster tempo.1 The same appearance of futility has occasionally misled sophisticated biologists. In his elegant book Wetware, the molecular and cell biologist Dennis Bray (2009) describes cycles in the nervous system:

In a typical signaling pathway, proteins are continually being modified and demodified. Kinases and phosphates work ceaselessly like ants in a nest, adding phosphate groups to proteins and removing them again. It seems a pointless exercise, especially when you consider that each cycle of addition and removal costs the cell one molecule of ATP—one unit of precious energy. Indeed, cyclic reactions of this kind were initially labeled “futile.” But the adjective is misleading. The addition of phosphate groups to proteins is the single most common reaction in cells and underpins a large proportion of the computations they perform. Far from being futile, this cyclic reaction provides the cell with an essential resource: a flexible and rapidly tunable device. [p. 75]

The word “computations” is aptly chosen. Computer programmers have been exploring the space of possible computations for less than a century, but their harvest of invention and discovery so far includes millions of loops within loops within loops. It turns out that all the “magic” of cognition depends, just as life itself does, on cycles within cycles of recurrent, “re-entrant,” reflexive information-transformation processes ranging from the nano-scale biochemical cycles within each neuron, through the generate-and-test cycles of predictive coding in the perceptual systems (see Clark, 2013, for a brilliant survey), to the whole brain sleep cycle, large-scale waves of cerebral activity and recovery that are revealed by EEG recordings. The secret ingredient of improvement everywhere in life is always the same: practice, practice, practice.

It is useful to remember that Darwinian evolution is just one kind of accumulative, refining cycle. There are plenty of others. The problem of the origin of life can be made to look insoluble (“irreducibly complex”—Behe, 1996) if one argues, as Intelligent Design advocates have done, that since evolution by natural selection depends on reproduction, there cannot be a Darwinian solution to the problem of how the first living, reproducing thing came to exist. It was surely breathtakingly complicated, beautifully designed—it must have been a miracle. If we lapse into thinking of the pre-biotic, pre-reproductive world as a sort of featureless chaos of chemicals (like the scattered parts of the notorious jetliner assembled by a windstorm that creationists invite us to imagine), the problem does look daunting and worse, but if we remind ourselves that the key process in evolution is cyclical repetition (of which genetic replication is just one highly refined and optimized instance), we can begin to see our way to turning the mystery into a puzzle: How did all those seasonal cycles, water cycles, geological cycles, and chemical cycles, spinning for millions of years, gradually accumulate the preconditions for inaugurating the biological cycles? Probably the first thousand “tries” were futile, near misses. But as the wonderfully sensual song by George Gershwin and Buddy DeSylva reminds us, see what happens if you “do it again” (and again, and again).2

A good rule of thumb, then, when confronting the apparent magic of the world of life and mind is to look for the cycles that are doing all the hard work.

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1 Dale Peterson has drawn my attention to the fact that chimpanzee hammer stones get gradually polished by continual use over long periods of time, and this provides a good “missing link” in a series that begins with more or less randomly picking up a stone and smashing a nut with it, then choosing the best-shaped stone you can see in the vicinity for that job, then looking far and wide for a better-shaped stone, then noticing (with your naked eye and visual memory) that your favorite stone is getting better from use, until finally you reach the sophistication of setting out to shape a stone for an anticipated task.

2 The role of abiotic cycles in changing the probability of the emergence of reproducing cells is discussed in more detail in my “Evolution of Reasons” (forthcoming).