This is part five in a series taken from Louis' paper (downloadable here), which addresses common Christian misconceptions about the nature of science and its relationship to God's involvement in our world. Links to the first four parts are located on the side bar to the right.
Shaven Baby, Tinman, Pax-6 and Sonic-hedgehog.
Genes that behave like switches have important consequences for development (how an organism changes from a fertilized cell into an adult). They are often given whimsical names like shaven baby (which makes the embryo hair fall off) or tinman (which governs development of the heart; the name comes from The Wonderful Wizard of Oz) or sonic hedgehog (a mutation in this genes gives the embryo little spikes). The same gene often turns out to be used throughout the animal kingdom: you can take the pax-6 gene that controls eye development from a human and put it into the part of a fly that controls wings formation and the fly will make a (malformed) eye on its wing. The same gene that controls the formation of human arms also controls the formation of wings on birds, fins on fish, and legs on centipedes! Modifying the way these genes are “wired together” can lead to massive changes in an organism. The burgeoning new field of evo-devo (evolutionary developmental biology) studies how evolution exploits these “toolbox genes” to help generate the endless forms most beautiful we see around us. Much remains to be understood, but adjectives like remarkable, elegant, and awe-inspiring are apt.
Clay or Lego Blocks?
In a fascinating book proposing a “theory of facilitated variation,"1 biologists Marc Kirschner and John Gehrard point out that while the Modern Synthesis implicitly used the metaphor of clay—evolution could produce variation in almost any direction, but in very tiny steps—modern biology would be better served by the metaphor of Lego blocks: reusable connectable units are more constrained in what they can do, but you can generate useful new variation in much larger steps.
Selfish Genes, or Control on Many Levels?
The field of systems biology is challenging the reductionist bottom-up primacy that has dominated biological explanation over the last few decades. In a beautiful book, The Music of Life: Biology beyond the Genome (OUP 2006), Denis Noble, a remarkable polymath and one of the fathers of systems biology, takes the gene-centric view of his Oxford colleague Richard Dawkins to task. He asserts that we must look beyond the “selfish gene.” A better metaphor for understanding life is music, “a symphonic interplay between genes, cells, organs, body, and environment." Earlier on in the book he mischievously inverts a famous passage from Dawkins’ The Selfish Gene (OUP 2006).
Dawkins himself admits that there is no experiment that he knows of that could distinguish these two viewpoints.2 Nevertheless, this example does illustrate the power of metaphors: the concept of a “selfish gene” now permeates much popular thinking about evolutionary biology. There is a technical sense in which it is useful (e.g. in arguments about levels of selection3), but as a morally-freighted metaphor it is seriously misleading.
Evolution as a Tinkerer, or as an Engineer?
In a famous 1977 article entitled “Evolution as a Tinkerer,”4 the French Nobel prize winner Francois Jacob introduced a powerful metaphor for the way that evolution can, for example, co-opt existing processes towards new ends. Unfortunately this metaphor also carries overtones such as ad-hoc and sub-standard. These connotations are then reflected in public debates about evolution. Whether tinkering is the best vantage point from which to view evolution is also not at all clear. In a provocative paper entitled “Biological Networks: The Tinkerer as an Engineer,”5 the systems biologist Uri Alon showed how the biochemical networks that control cells display good engineering principles such as modularity, robustness, and the re-use of components. It should be kept in mind that the question of optimality is highly contested in evolutionary biology. To properly assess such questions one often needs consider counterfactuals, something that is much harder to do in biology than it is in say physics. Nevertheless, it seems to me that Jacob’s “tinkerer” metaphor is not nearly as widely applicable as some biologists claim.
Contingency or Inevitable Outcomes?
Wind back the tape of life to the early days of the Burgess Shale; let it play again from an identical starting point, and the chance becomes vanishingly small that anything like human intelligence would grace the replay.” In evolution, there is no direction, no progression. Humanity is dethroned from its exalted view of its own importance.
- Stephen J. Gould, Wonderful Life (W.W. Norton 1989)
When you examine the tapestry of evolution you see the same patterns emerging over and over again. Gould's idea of rerunning the tape of life is not hypothetical; it's happening all around us. And the result is well known to biologists—evolutionary convergence. When convergence is the rule, you can rerun the tape of life as often as you like and the outcome will be much the same. Convergence means that life is not only predictable at a basic level; it also has a direction. …..the constraints of evolution and the ubiquity of convergence make the emergence of something like ourselves a near-inevitability.
- Simon Conway Morris, Life's Solution: Inevitable Humans in a Lonely Universe (CUP, 2003)
These two quotes could not be more different. Regardless of the metaphysical implications, it is a very fascinating scientific question to ask which man is right. Gould’s view is widely shared among biologists and frequently repeated in public debate. However, Conway Morris, one of the heroes of Wonderful Life, lists an astonishing catalogue of examples of convergence—from antifreeze proteins to echolocation to social organization—where the same features emerge independently in evolution.
My favorite quote on this topic is by Natalie Angier in “When Nature Discovers The Same Design Over and Over,” NY Times, Dec 15 1998:
Nature is like Henny Youngman: She writes great jokes, and then flogs them again and again. Take the spiny anteater of Australia, the pangolin of Africa, and the giant anteater of Latin America (please!). Each of these mammals has a long, sticky, worm-like tongue, no teeth to speak of and scimitar claws. Each has bulging salivary glands, a stomach as rugged as a cement mixer and an absurd, extenuated, hairless snout that looks like a cross between a hot dog and a swizzle stick […] Despite their many resemblances, the three creatures are unrelated to one another; the spiny anteater, in fact, lays eggs and is a close cousin of the duck-billed platypus. What has yoked them into morphological similitude is a powerful and boundlessly enticing process called evolutionary convergence. By the tenet of convergence, there really is a best approach and an ideal set of tools for grappling with life's most demanding jobs. The spiny anteater, pangolin and giant anteater all subsist on a diet of ants and termites, and myrmecophagy, it turns out, is a taxing, specialized trade. As a result, the predecessors of today's various ant hunters gradually, and quite independently, converged on the body plan most suited to exploit a food resource that violently resists exploitation.
This series is not the right forum to discuss the scientific implications of all this convergence. What is clear, I hope, is that evolution appears to be much more constrained than earlier generations of scientists may have thought.
So What Shall We Make of All These Metaphors?
One could describe evolution as a blind, purposeless, and directionless process that tinkers by modifying the genetic blueprints that determine our infinitely malleable biological outcomes. By a combination of random chance and survival of the fittest it stumbles upon contingent organisms best described as secondary phenomena cobbled together by selfish genes.
Or one could instead describe evolution as “a symphonic interplay between genes, cells, organs, body, and environment” that wires a toolkit of Lego-like components into interacting networks in order to explore a highly structured search space. The (inevitable?) outcome of this stochastic process is the emergent self-assembly of the “endless forms most beautiful” that include you and I.
The fact that there are so many different metaphors reflects the many facets of evolutionary processes. Christians may find some of these metaphors more palatable than others.6 But it must be kept in mind that all these metaphors, even those with which Christians would be more comfortable, are limited in their ability to fully capture the detailed scientific mechanisms at work. Nevertheless, familiarity with a broader spectrum of metaphors can help a Christian recognize the rhetorical subterfuge of those who pick specific metaphors over others in order to advance ideological agendas. The most important point of this section is, however, that all these metaphors are severely restricted in what they can tell us about where we come from and how we should then live.