Still others see God as having to interfere sporadically in evolution, guiding it in various ways we’ll discuss below. Divine interventions are deemed necessary to ensure both the initial appearance of life and the eventual appearance of humans, for such matters simply couldn’t be left to naturalism. And this view shades insensibly into intelligent design (ID), the modern version of creationism that, while accepting a limited amount of evolution within species, insists that garden-variety Darwinian evolution simply can’t explain some “irreducibly complex” features like the blood clotting system of vertebrates or the complicated whiplike tails (flagella) that propel some bacteria.
While ID arguments have been refuted by scientists, versions of theistic evolution keep popping up like heads on the Lernaean Hydra, for believers are tenacious. Yet all of these versions come perilously close to ID creationism. One of them is the Catholic Church’s insistence that God intervened at least once in the human lineage to insert a soul. This remains church dogma, expressed by Pope John Paul II in his famous 1996 message to the Pontifical Academy of Sciences:
With man, we find ourselves facing a different ontological order—an ontological leap, we could say. But in posing such a great ontological discontinuity, are we not breaking up the physical continuity which seems to be the main line of research about evolution in the fields of physics and chemistry? . . . But the experience of metaphysical knowledge, of self-consciousness and self-awareness, of moral conscience, of liberty, or of aesthetic and religious experience—these must be analyzed through philosophical reflection, while theology seeks to clarify the ultimate meaning of the Creator’s designs.
It’s hard to see this “ontological discontinuity”—the endowment of humans with a metaphysical soul—as anything other than creationism. Granted, it may have been a one-time intervention, but it still mixes science with religion, weakening the claim that Catholicism is compatible with evolution. With respect to evolution, the position of the Catholic Church differs from biblical creationism only in the amount of God’s intervention.
Finally, some theistic evolutionists hold a “constant tweaking” model: God interferes frequently in evolution, tugging it, like an errant dog that won’t take to its leash, in prescribed directions. These could involve preserving endangered species, creating new mutations, or tinkering with genes or environments. These interventions have two features: they are undetectable, rendering them immune to scientific investigation, and they are invariably used to give God a way to ensure the evolution of humans. Kenneth Miller suggested that this could occur if God simply fiddled with the movement of electrons:
Fortunately, in scientific terms, if there is a God, He has left himself plenty of material to work with. To pick just one example, the indeterminate nature of quantum events would allow a clever and subtle God to influence events in ways that are profound, but scientifically undetectable to us. Those events could include the appearance of mutations, the activation of individual neurons in the brain, and even the survival of individual cells and organisms affected by the chance processes of radioactive decay.
It’s ironic that Miller, who has produced some of the most compelling and convincing arguments against intelligent design, finally winds up touting God as using quantum mechanics to guide evolution. In this way he’s camping on the outskirts of creationism. And why would God want to act in a “clever and subtle” (i.e., sneaky) way? Why is that better than creating humans de novo? The only advantage of Miller’s theory is that God’s interventions are conveniently undetectable.
Theistic evolution fails to harmonize science with religion because it pollutes evolution with creationism, positing interventions by God that are either scientifically refuted or untestable—and therefore superfluous. That is why, though eagerly embraced by the American public, theistic evolution has been completely rejected by scientists. Imagine if we had equivalents in other fields, like “theistic chemistry,” proposing that God undetectably forges bonds between molecules, or “theistic gravity,” claiming that the attraction between objects is maintained by a Ground of Being. Nobody, even believers, would take this seriously. The only reason why theistic evolution has gained traction is because it’s politically expedient (scientists don’t mind it because it gives religious people a foot in the evolution camp), and because for believers it removes some of the sting from naturalistic evolution. Believers don’t propose the notions of theistic chemistry and physics only because those fields don’t conflict with scripture. Only biology has theories that strike down the human exceptionalism touted in sacred texts.
But theistic evolution is also riddled with scientific problems. The big one is that despite adherents’ claims that mutations in our DNA are biased in a given direction (i.e., are “nonrandom”), there is no evidence that useful mutations crop up more often when the organism “needs” them. Mutation would, for instance, be nonrandom if mammals moving to a colder environment experienced relatively more mutations producing longer fur. But there’s no evidence for that. As far as we know, the mutational process appears to be “indifferent” (a term I prefer over “random”): errors occur in an organism’s DNA regardless of whether they’d be good or bad for its survival and reproduction. While one could save theistic evolution by arguing that God-created mutations are undetectably rare—in effect, miracles—that’s not a testable hypothesis. What we have shown, in experiments with microorganisms, is that no external force seems to be producing mutations in an adaptively useful way.
Further, evolution doesn’t show the signs of teleological guidance or directionality proposed by theistic evolutionists. Evolutionary biologists long ago abandoned the notion that there is an inevitable evolutionary march toward greater complexity, a march culminating in humans. If one considers all species together, the average complexity of organisms has certainly increased over the 3.5 billion years of evolution, but that’s just because life began as a simple replicating molecule, and the only way to go from there is to become more complex.
Contrary to popular wisdom, complexity isn’t always favored by natural selection. If you are a parasite, for instance, natural selection may make you less complex, for you can live largely off the exertions of another species. Tapeworms evolved from free-living worms, and during their evolution have lost their digestive system, their nervous system, and much of their reproductive apparatus. Yet tapeworms are superbly adapted for a parasitic way of life: they simply pump out eggs and let their host do much of the metabolic work.
It doesn’t always pay to be smarter, either. For some years I had a pet skunk, who was lovable but didn’t seem very bright: in fact, sometimes he seemed to be unaware of anything but food. I mentioned this to my vet, who put me in my place with a sharp retort: “Stupid? Hell, he’s perfectly adapted for being a skunk!” Intelligence comes with a cost: you need to produce and carry that extra brain matter, and crank up your metabolism to support it. When this cost exceeds the genetic payoff, the brain won’t get larger. A smarter skunk might not be a fitter skunk. There are many cases in which organisms have lost features, becoming simpler because such loss was favored by natural selection. Organisms that invade caves often lose their eyes, for it’s no advantage to have a useless organ that, besides being easily injured, can divert resources from other parts of the body that are useful. Remember that the currency of natural selection is reproductive output, and sometimes reproduction is enhanced by evolution’s removal of features that aren’t useful.
Finally, we know of no natural or supernatural process that drives evolution in certain directions; in fact, sometimes natural selection can drive species extinct, by adapting them to environments that are vanishing. I suspect that polar bears will go this route as global warming proceeds.
When thinking about evolutionary “direction,” we should remember that there are just two important evolutionary mechanisms, natural selection and genetic drift. Drift is simply random changes in the proportions of genes caused
by the vagaries of reproduction: it’s the genetic equivalent of flipping coins. If different forms of genes (say, those producing blue versus brown eyes) made no difference to your number of offspring, the proportions of those genes in a population would simply fluctuate at random. This process is nondirectional by definition, and cannot produce adaptation.
The other mechanism, of course, is natural selection, which is nonrandom and does promote adaptation. Selection produces changes in traits that give an organism a reproductive advantage in its current environment. Although that process can occasionally be directional, as in an evolutionary “arms race” when predators and prey evolve higher efficiency in killing and avoiding each other respectively, the directionality is due not to God but to environments in which there’s only a single way to improve. When the climate becomes colder—and major glacial cycles occur every hundred thousand years or so—organisms must adapt to low temperature or face extinction. When things warm up, the evolutionary direction is reversed. If theistic evolution is to be a truly coherent theory, its proponents must do more than raise it as a theoretical possibility: they must explain what mechanism makes evolution directional, guiding it toward humans, and show us how and where God intervened in that process.
An important claim of many theistic evolutionists, whether or not they invoke God’s intervention, is that the evolutionary appearance of humans on Earth was inevitable. But that argument also dissolves under scrutiny.
Was the Evolution of Humans Inevitable?
If science can make a plausible case that the naturalistic evolution of humans, or of creatures with similar mental faculties, was inevitable, then theistic evolutionists get a big break. In that case we’d no longer need to invoke supernatural intervention to produce our species, for humans, or something like them, would always appear after sufficient evolutionary time. This would produce, through a purely material process, just what theists need: a complex and rational creature who apprehends and worships God. (Let’s call such creatures “humanoids.”) That leaves the naturalism in biology but still produces the outcome theists want. It’s important, then, to see how far science supports the notion of human inevitability. Indeed, if we can’t show that humanoid evolution was inevitable, then the reconciliation of evolution and Christianity collapses, for if we’re really the special objects of God’s creation, our appearance must have been guaranteed by either God or nature.
How can science address the question of whether naturalistic evolution would always produce a species like ours? One way is to assume that there was a preexisting but unfilled ecological niche for a humanoid creature, and that evolution would eventually work its way into filling that gap. But scientists aren’t at all sure whether there are “empty niches” that precede the evolution of the organisms that fill them. After all, some organisms create their own niches through their evolved behavior, so the niches evolve along with the organism. The classic example is the beaver, which, by evolving the ability to chew down trees and assemble them into a dam, created its own lake habitat and food reservoir, complete with an enclosed house. That niche didn’t exist before beavers, but was created by their ancestors, and has affected their subsequent evolution.
Given the quirky history of life, it’s impossible to predict what new creatures will evolve. Who would have predicted, for instance, that two groups of birds, one in the New World and the other in Africa and Asia (the hummingbirds and sunbirds, respectively), would independently evolve the ability to hover like helicopters before flowers, drinking the nectar with long beaks and tongues? And even if we can identify things that look like empty niches, we don’t know if organisms have the physiological equipment, or the right mutations, to evolve a way of life that seems available and adaptive. There are no examples of snakes that eat vegetation, for instance, yet there are many snakes and a lot of grass and leaves. Can we assert with confidence that if we wait long enough, the evolution of grass-eating snakes is inevitable?
Still, in many cases organisms must adapt to a relatively unchanging environment, and so we can sensibly speak of at least some aspects of a niche, or way of life, to which animals and plants must adapt. Mobile organisms that live in the sea, for example, must evolve ways to swim and to get oxygen while in the water. The strongest evidence for such preexisting niches is the phenomenon of “evolutionary convergence,” often invoked to support human inevitability.
The idea is simple: species often adapt to similar environments by independently evolving similar features (“convergences”). Ichthyosaurs (ancient marine reptiles), porpoises, and fish all evolved independently in the water, and through natural selection all acquired strikingly similar streamlined shapes. Complex “camera eyes” evolved separately in both vertebrates and squid. Arctic animals such as polar bears, arctic hares, and snowy owls are either permanently white or turn white in the winter, hiding them from predators or prey. This camouflage, too, evolved independently in each lineage.
Perhaps the most astonishing example of convergence is the similarity between some species of marsupial mammals in Australia and unrelated placental mammals that live elsewhere. The marsupial flying phalanger looks and acts just like the flying squirrel of the New World. Marsupial moles, with their tiny eyes and big burrowing claws, are dead ringers for our placental moles. Until it went extinct in 1936, the remarkable thylacine, the pouched Tasmanian wolf, looked and hunted like the conventional placental wolf.
Convergence tells us something deep about evolution. There must be at least some preexisting “niches,” or habitable environments, that call up similar evolutionary changes in unrelated species. That is, starting with different ancestors and fueled by different mutations, natural selection can nonetheless mold unrelated creatures in very similar ways—so long as those changes improve survival and reproduction. There were niches in the sea (probably involving lots of nutritious marine prey) for mammals and reptiles, so porpoises and ichthyosaurs became streamlined. Animals in the Arctic improve their survival if they are white in the winter. And there must have been niches for small omnivorous mammals that glide from tree to tree.
Convergence is one of the most impressive features of evolution, and it is common: there are hundreds of cases, thoroughly documented in paleontologist Simon Conway Morris’s book Life’s Solution: Inevitable Humans in a Lonely Universe. But the subtitle gives a key to its thesis: Conway Morris is a devout Christian who sees humanoids as something that evolution would inevitably produce:
Contrary to popular belief the science of evolution does not belittle us. As I argue, something like ourselves is an evolutionary inevitability, and our existence also reaffirms our one-ness with the rest of Creation.
This view is echoed by Kenneth Miller:
But as life re-explored adaptive space, could we be certain that our niche would not be occupied? I would argue that we could be almost certain that it would be—that eventually evolution would produce an intelligent, self aware, reflective creature endowed with a nervous system large enough to solve the very same questions we have, and capable of discovering the very process that produced it, the process of evolution. . . . Everything we know about evolution suggests that it would, sooner or later, get to that niche.
But my own understanding of evolution suggests otherwise. I see the proper answer to the question “Is the evolution of humanoids inevitable?” as “We don’t know, but it’s doubtful.” There are in fact good reasons to think that the evolution of humanoids was not only not inevitable, but a priori improbable. The reason is this: although convergences are common features of evolution, there are at least as many failures of convergence. These failures aren’t impressive simply because they involve species that are missing. Consider Australia again. Although there are many convergences between placental mammals and Australian marsupials, there are also many types of mammals that evolved elsewhere that have no equivalents among marsupials. There is no marsupial counterpart to a bat (that is, a flying pouched m
ammal), or to giraffes and elephants (large pouched mammals with long necks or noses that can browse on the leaves of trees). Most tellingly, Australia evolved no counterpart to primates, or any creature with primatelike intelligence. In fact, Australia has many unfilled niches—and hence many unfulfilled convergences, including that prized “humanoid” niche. If high intelligence was such a predictable result of evolution, why did it not evolve in Australia? Why did it arise only once—in Africa?
That raises another question. We recognize convergences because unrelated species evolve similar traits. In other words, the convergent traits appear in two or more species. But sophisticated, self-aware intelligence is a singleton: it evolved just once, in a human ancestor. (Octopuses and dolphins are also smart, but they do not have the stuff to reflect on their origins.) In contrast, eyes have evolved independently forty times, and white color in Arctic animals several times.
While the convergence argument can support the view that some evolutionary pathways are more probable than others, that argument rests on the existence of similar traits that evolve independently in more than one group. It cannot, then, be used to claim that a feature that evolved only once (i.e., our complex mentality) was inevitable. The elephant’s trunk, an intricate and sophisticated adaptation—it has more than forty thousand muscles—is also an evolutionary singleton, as are feathers. Yet you don’t hear scientists arguing that evolution would inevitably fill the “long-proboscis niche” or the “feathered-animal niche.” Conway Morris, Miller, and others proclaim the inevitability of humanoids for one reason only: their religion demands it.
The most famous proponent of the noninevitability of evolution was Stephen Jay Gould. In his book Wonderful Life: The Burgess Shale and the Nature of History, Gould argued that the only real way to test whether the evolution of any species (like humans) was inevitable would be to start evolution over and over again, replaying the “tape of life” to see if humans always appeared. That, of course, is impossible, for we’re stuck with only one realization of the evolutionary process.
Faith Versus Fact : Why Science and Religion Are Incompatible (9780698195516) Page 19