Three Big Bangs Page 9
Perhaps it all takes place by slight modifications of a precursor system. But these slight modifications are now being made in new, unprecedented directions. The co-opting modification is not improving the initial function but angles off in a new direction. The change is not iterative; it is metamorphic. Co-option breaks up channelized and entrenched developmental lines and opens up new directions. Restriction enzymes, one of the most important features of genetic innovation and a principal tool in genetic engineering, were first invented by bacteria to cut their parasites into pieces. They turned out to be useful for organisms to cut their own genomes into pieces and reshuffle them in the search for co-options.
Environmental and structural constraints remain but the constraints are not what they were before, now that the organism is equipped with these new potential capacities. The amount of information in an organism is transforming into its capacity for self re-formation, though the self-re-formation is also provoked, evoked by environmental challenge and stress. Self-organizing becomes self-transcending.
Co-option can escalate cybernetic capacities. Consider the evolution of hearing, vital for animals needing information about their world (Bear, Conners, and Paradiso 2001:chapter 11). Hearing evolved from cells in the side of an aquatic vertebrate’s body that were sensitive to pressure, helpful to a swimming animal, an original use that has been lost from the reptiles onward. These cells were co-opted to become the hair cells in mammalian ears. That required constructing the external, middle, and inner ears, with small bones co-opted and modified to amplify sound, vibrating an oval area on the cochlea of the inner ear. This jiggles the microscopic hairs (stereocilia) on the ends of the hair cells. These cells synapse with neurons. The hairs are sensitive to movements as small as 0.3 nanometers (about the diameter of a large atom). Mechanical movement of the cilia opens and closes ion channels, letting sodium ions into the cell, and this constitutes an electric current, which triggers the synapsizing, producing perceptible noise, over a volume differential of a trillion times from softest to loudest.
Animals need to know frequencies as well as volume, and here the firing frequencies of the usual synaptic transmissions can track frequencies at the lower ranges, but the higher frequencies are too fast for this method. So ears improvise something else. There has further evolved a basilar membrane packed with hair cells and rolled up in the cochlea (about the size of a pea) that, using different widths and stiffness of the membrane, can differentiate how far along it a traveling wave will go, and so the auditory system responds to different frequencies ending up at different places on the membrane. There is a tonotopic map on the basilar membrane of the frequencies being heard. Further, there is a system of outer hair cells that amplify the inner hair cells. With this the ear can detect frequencies up to 20,000 hertz. A trained musician can distinguish between a tone of 1,000 Hz and another of 1,001 Hz, which requires detecting a difference of only 1 microsecond in the sound wavelengths.
But where is the sound coming from? That too is useful information. Animals have two ears, and the differential travel time of sound from the source to the slightly separated ears can be used to locate the source. But again, this only works in the range 20–2,000 hertz, above which frequency the wavelength is too short to figure location out this way. There is not enough interaural time. So another way is improvised. One ear is in the shadow of the sound, compared to the other. Now the auditory system sends the signals to the superior olive nucleus in the mid-brain, and there the sound from one ear is compared to the sound from the other for the intensity differential resulting from the sound shadow, and the location of higher-frequency sounds is computed. Humans can locate a sound source in the horizontal plane with a precision of 2 degrees (Bear, Conners, and Paradiso 2001:chapter 11). Meanwhile, a spin-off from this auditory system is the vestibular system, used to maintain bodily balance.
One could say that such complex ears were latent in the possibility space of pressure cells, which were latent in the possibility space of carbon, oxygen, nitrogen, and phosphorus atoms. But an equally plausible account is that co-options opened up new possibility space, and the new genetic information achieved proves of value in an evolutionary search for better environmental information. Ears open up the possibility of animal detection of information about their environment, and, in due course, of animal communication.
Anticipating developments during the third big bang, with continuing co-option, much later, ears developed to make possible human language, which makes culture possible, with its cumulative transmission of ideas orally communicated from mind to mind. Escalating co-option drives the information explosion. There are critical turning points in the history of life that hinge on events more idiographic (unique, one-off events) than nomothetic (lawlike, inevitable, repeatable trends). The main idea in co-option is the unpredictable and unexpected; co-option is as revolutionary as it is evolutionary.
Evolutionary Headings: Surprising or Inevitable?
Is evolution going anywhere? If so, are these origins and headings surprising or inevitable? Reflecting on the second big bang, we must return to the same sort of questions about which we puzzled with the first big bang, but now there are more complex dimensions. Something seems to be introducing, layer by layer, new possibilities of order, not just unfolding some latent order already there in the startup. The biological constructions are historical, but they are not simply linear combinatorial processes. True, in the DNA molecules the coding is linear, and the changes are incremental in the linear sequences. But these changes also involve reassorting blocks that reshuffle to produce surprises. A few changes in the linear sequence, resulting from mutations, produce quite different folding patterns at tertiary and quaternary levels in the finished protein (Perutz 1983). Novel possibilities open up whole new regions of search space; old molecules recombine to learn new tricks in unprecedented circumstances. Evolution improvises, sometimes with serendipity.
Evolutionists can make ex post facto explanations. After the events have taken place, the paleontologists can say, well, this is what happened, and this is what resulted. But prior to the events, if asked what would be the result if such and such happened, one could not always, from the knowledge of the constituent parts, predict in advance what the results will be. Much less could one predict that such results had to happen. Perhaps one will say, since it has so often happened in evolutionary history, that there must be some disposition in biological nature to improvise, to be opportunistic, some tendency to co-opt.
But where is such tendency located? Hardly from “bottom up” in the precursor materials, inherited from the first big bang, even with their atomic and chemical possibilities. Hardly either from “top down” in the planetary geological or meteorological systems, likewise inherited from inanimate nature. Ecologists think that environments stimulate speciation. The most obvious cybernetic process lies in genetics, so maybe the possibilities lie in the mid-scale genetics. Steven M. Stanley, in his survey of evolutionary speciation, concludes that even more than being environmentally driven, “The system has been essentially internally driven.” He finds, with emphasis, “evidence of great resilience of the intrinsic rates of origination and extinction that characterize individual taxa” (Stanley 2007:3, 31). The motor of change is not simply challenging environments but prolife organismic drive. Survival of the fittest drives arrival of the more fit, which drives escalating biodiversity and biocomplexity.
So is Darwinian natural selection a sufficient explanation of the emergence of complexity over time? Darwinian natural selection once did not exist; it also had to emerge, at the origin of life. Once under way, across evolutionary natural history the innovations have never violated natural selection; there is always (in principle at least) an explanation in terms of natural selection—at least retrospectively. But prospectively, might the origin and evolution of life have been predicted? Elements of chance and drift appear, and natural selection itself involves elements of randomness, as in mutations. Conte
mporary biologists are divided across a spectrum whether this creative cybernetic evolutionary history is entirely contingent or quite probable, even inevitable. Francis Crick, after reflecting that the origin of life seems “almost a miracle,” continues: “At the present time we can only say that we cannot decide whether the origin of life was an extremely unlikely event or almost a certainty—or any possibility in between these two extremes” (Crick 1981:88).
At one end, famously, Jacques Monod, Nobel prize-winning biologist, insists: “Chance alone is at the source of every innovation, of all creation in the biosphere.” Evolutionary history is “the product of an enormous lottery presided over by natural selection, blindly picking the rare winners from among numbers drawn at utter random” (Monod 1972: 112, 138). That is natural selection with unpredictable results. Similarly and equally famously, Stephen Jay Gould, Harvard paleontologist, looking at the Cambrian explosion, particularly as recorded in fossils found in the Canadian Burgess Shale, concludes: “Almost every interesting event of life’s history falls into the realm of contingency” (Gould 1989:290). “We are the accidental result of an unplanned process… the fragile result of an enormous concatenation of improbabilities, not the predictable product of any definite process” (Gould 1983:101–102). Life evolves by stumbling around.
Others argue that the chance that complex systems evolve only by chance is vanishingly small. There may be randomness; there is also selection. But of what kind? Simon Conway Morris, eminent Cambridge University paleontologist who did the detailed work on the fossil animals in the Burgess Shale that Gould uses, draws conclusions that are the “exact reverse” (Conway Morris 2003:283). This is one of the more philosophically remarkable happenings in contemporary paleontology. We almost get slapped in the face with what radically different metaphysical frameworks eminent biologists (Harvard versus Cambridge, in this case) can read into, or out of, the same evolutionary facts (Conway Morris and Gould 1998).
Contingency disappears, Conway Morris argues, when we look at the remarkable convergences that have characterized evolutionary history. For example, marsupials evolved in Australia parallel to the evolution of placentals worldwide, some doglike, some catlike, some rodent-like. (Though here we might wonder why kangaroos and wallabies, quite successful marsupials, have no analogs among the placentals.) Eyes, ears, legs, wings appeared more than once. Some species of birds got smarter, so did some species of primates, with very different brain anatomies. If evolution on Earth happened all over again, life would begin in the sea and move to land. There would be plants and animals, predators and prey, genetic coding, sexuality. Sentience would appear in some forms, based on something like neurons, and some of these sentient forms would become increasingly intelligent. So, whatever the contingencies, there must be selection for such events.
Looking back across Earth’s natural history and wondering if things might have been otherwise, searching the possibilities for “evolutionary counterfactuals,” Conway Morris concludes: “possibly… we shall discover in the end that there are none. And, despite the almost crass simplicity of life’s building blocks, perhaps we can discern inherent within this framework the inevitable and pre-ordained trajectories of evolution?” (Conway Morris 2003:24). “The details of convergence actually reveal many of the twists and turns of evolutionary change as different starting points are transformed towards common solutions via a variety of well-trodden paths” (Conway Morris 2003:144). Interestingly now, despite the impressively escalating biodiversity, there is something of a counterclaim. The search space, the maneuvering space, is limited; there are only so many niches to occupy. There are constraints, a limited number of best solutions to problems that organisms repeatedly face, so species will often converge. But the constraints still seem to lead upward.
Christian de Duve, also a Nobel prize-winning biologist, finds “landmarks on the pathways of life” that he calls “singularities,” the major changes in the history of life (de Duve 2005). He is not thinking only of one-off anomalous events, as others may who use that word. He rather finds the repeated returning of constraints that force a channeling that escalates evolutionary constructions: bottlenecks, environmental constraints, morphological constraints, enzyme functions, molecular structures, “similar singularities,” we might call them, as well as, sometimes, what he calls “fantastic luck.” These unique features stack up again and again to push up and up, converting chance to the near certainty of startling creativity on Earth, not only in origins but also in trajectories.
de Duve concludes:
Life was bound to arise under the prevailing conditions, and it will arise similarly wherever and whenever the same conditions obtain. There is hardly any room for “lucky accidents” in the gradual, multistep process whereby life originated…. I view this universe [as]… made in such a way as to generate life and mind, bound to give birth to thinking beings. (de Duve 1995:xv, xviii)
It is self-evident that the universe was pregnant with life, and the biosphere with man. (de Duve 2002:298)
de Duve replies to Jacques Monod’s claims about life originating only by chance (cited earlier): “To Monod’s famous sentence: ‘The universe was not pregnant with life, nor the biosphere with man,’ I reply: ‘You are wrong. They were’” (de Duve 1995:300). “The universe has given life and mind. Consequently, it must have had them, potentially, ever since the Big Bang” (de Duve 2002:298). Again we find prominent biologists in radical disagreement.
Evolutionists here often appeal to deep time, over which eons the unlikely may become likely, even inevitable. Longer time spans do not necessarily help to make the improbable probable, especially where the breakdown rate of the novel constructions always overwhelms the construction rate. This is often problematic when the promising evolutionary constructions are unstable or metastable (temporarily stable). Nevertheless, deep time does give more opportunity for convergence, constraints, channeling to become likely. Rather like cosmologists who, encountering the first big bang, posit a host of multiple universes so that this random one can be less surprising, now the evolutionary biologists posit a host of random mutations endlessly testing life possibilities, and find the emergence and escalation of life on Earth less surprising.
But do such convergences and constraining singularities add up to making the whole life story more or less inevitable? Within the cell Conway Morris notices “some of the proteins being recruited in quite surprising ways from some other function elsewhere in the cell” (Conway Morris 2003:111). “Evolution is a past master at co-option and jury-rigging: redeploying existing structures and cobbling them together in sometimes quite surprising ways. Indeed, in many ways that is evolution” (Conway Morris 2003:238). But now it seems not so much that constraints force convergence as, rather, that co-option finds surprising ways to get past earlier constraints. Radical new possibilities open up. Here Conway Morris backs off: “Hindsight and foresight are strictly forbidden… we can only retrospect and not predict” (Conway Morris 2003:11–12). So can he, after all, “discern inherent… the inevitable and pre-ordained trajectories of evolution?” (Conway Morris 2003:24).
Some events are “quite surprising” indeed. About 2.7 billion years ago (Ga) eucaryotes developed from the ongoing procaryote line. This required radical reorganization of the cell, and seems to have happened only once. Nucleated cells are typically ten times larger in diameter and a thousand, even ten thousand, times larger in volume than non-nucleated cellular organisms. By some accounts this was as innovative as any other discovery in the history of life, because, by concentrating the genetic material, this launched radical new cybernetic possibilities for its elaboration. Christian de Duve traces “this astonishing evolutionary journey.” “The consequences of this event were truly epoch-making…. Without the emergence of eucaryotic cells, the whole variegated pageantry of plant and animal life would not exist, and no human would be around to enjoy that diversity and to penetrate its secrets” (de Duve 1996:50).
Much later
, but before plants and animals had diverged, by endosymbiosis what were once-independent organisms fused into other, larger and quite different organisms to become mitochondria transferred into the pre-plant/animal line, and became the powerhouse organelles for all subsequent life (fig. 2.12; data from Dyall, Brown, and Johnson 2004).
Figure 2.12 Evolutionary development by endosymbiosis
There emerged a new kind of system where the organism has highly efficient and specialized power modules (the mitochondria), something not possible for either of the precedents before they interacted, crisscrossed, synthesized, and transformed each other. The “information” about how to do this was not present before in the preceding organisms, but now there appears new “information” (coded in the revised DNA in the nucleus and the residual DNA in the mitochondrion) that makes this new, high-powered form of life possible.
About 1.6 billion years ago the plant and animal lines diverged; and later still, by another remarkable endosymbiosis this time plastids, once free-living, made the lateral transfer into the plant line to become the chloroplasts critical for the capture of solar energy. Again, new, higher-powered forms of life became possible, both in the plants and in the animals that feed on plants (Dyall, Brown, and Johnson 2004). Perhaps one can say that endosymbiosis is likely to occur: there are frequently “mobile elements” that transpose and reshape evolution (Kazazian 2004). But is there any “inherency” in the earliest microbial life making inevitable or even probable these two especially vital endosymbioses, both thought to have initiated as singularities and both dramatically changing the history of life on Earth?
One can say that evolution is disposed to exciting serendipity. In such cases of co-opted emergence, repeatedly compounding, something that is genuinely new pops out, pops up. The novelty is, of course, based on the precedents, but there is genuine novelty not present in any of the precedents. The presence of the prior organisms was required, but did not determine or make inevitable these results.