Faith Versus Fact : Why Science and Religion Are Incompatible (9780698195516) (24 page)

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 mammal), 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.

But there are other ways to judge whether evolution is repeatable in this way. One way is to understand how the process works, an understanding that, combined with some knowledge of physics, suggests that the tape of life would play out differently each time, even if started under identical conditions.

Like many biologists, Gould argues that evolution is “a contingent process.” The way natural selection molds a species depends on unpredictable changes in climate, on random physical events such as meteor strikes or volcanic eruptions, on the occurrence of rare and random mutations, and on which species happen to be lucky enough to survive a mass extinction. If, for example, a large meteor had not struck the Earth sixty-five million years ago, contributing to the extinction of the dinosaurs—and to the rise of the
mammals they previously dominated—all mammals might still be small nocturnal insectivores, munching on crickets in the twilight. And there would be no humans. Based on this contingency, Gould concluded the evolution of humans was “
a wildly improbable evolutionary event” and “a cosmic accident
.”

But is evolution
really
“contingent”? That depends on what you mean by the word. Evolution is certainly
unpredictable,
because we don't know exactly how the environment will change or what mutations will occur. But “unpredictable” is not identical to “not predetermined.” Most scientists are physical determinists, accepting that the behavior of matter, at least on the macro level (stuff that humans can perceive), is absolutely determined by the configuration and laws of the universe. We can't always predict the weather, for instance, but that's only because we can't know everything about what affects climate, including temperature and winds at every spot on Earth. It's possible that if we had perfect knowledge of such things—which now include the human behavior that contributes to global warming—we could accurately predict the weather years in advance (even with our present sophisticated instruments, we can barely predict it a day in advance). Likewise, it was certainly determined well in advance that the asteroid that snuffed out the dinosaurs would strike the Earth about sixty-five million years ago in the vicinity of the Yucatán Peninsula.

The point is that even if evolution is “contingent,” that doesn't mean “it's not determined in advance,” but only that “we don't know enough to predict it.” It's likely, then, that the course of evolution is determined by the laws of physics. And that might imply that those laws would, given identical starting conditions, always yield identical products—including humans.

But there's still one hitch, and it's an important one. It involves quantum mechanics, which tells us that on the microscopic level of particles like electrons or cosmic rays (mostly fast-moving neutrons), things are
not
determined, but are
fundamentally and unpredictably indeterminate
. If you took a lump of radioactive uranium, for instance, and could observe when each atom decayed, and then restarted the whole scenario with the same lump, you'd find that during the rerun different atoms would decay, and you'd never be able to predict which ones. (The
ensemble
of atoms, however, does obey statistical laws, so that the “half-life” of a radioactive
element—the time needed for half the atoms to decay—is always the same.) Thus although a large
group
of atoms decays at a constant rate, it's impossible to predict which atoms will go first and which later. Such statistical regularities but individual indeterminacy are characteristic of quantum mechanical phenomena, including radioactive decay.

The question of whether humans were inevitable, then, boils down to the question of whether evolution is repeatable and deterministic, and that can be further reduced to the question of whether evolution is affected by the genuine indeterminacy of quantum mechanics. And it most likely is—in two important ways. The first involves whether the Earth would exist in the first place if the Big Bang were repeated under the same starting conditions. The answer is almost certainly no. Rerunning the history of the universe would probably result in a general similarity to what we have now (perhaps similar numbers of stars and galaxies, for instance), but it's very unlikely that the Earth and Sun would exist as the same objects they do now. If we can't even repeat the appearance of our solar system after a replay of the Big Bang, then all bets are off: there's no assurance that life as we know it would evolve. One might argue that life would still evolve on
some
planets in the universe, but there's no guarantee that that kind of life would be humanoid—the “image of God.”

But there's another part of evolution that's also subject to the vagaries of quantum indeterminacy: mutations. Mutations are molecular changes in the DNA, many of them errors that occur when DNA replicates, which by changing the genetic code produce the new forms of genes that fuel evolution. And some factors that produce mutations, like X-rays, cosmic radiation, or even the simple errors in pairing of the DNA double helix, are probably affected by unpredictable quantum-level events.

What this means is that if life began all over again, even on our primitive Earth, the mutations that are evolution's raw material would be different. And if the raw material of evolution differed, so would its products: all the species alive today. All it would take is a few different mutations occurring early in the history of life, for instance, and everything that followed might have been very different from what actually evolved.

The upshot is that if mutations are fundamentally indeterminate, a
replay of evolution would likely give us an array of species very different from those we see today. And we couldn't be sure at all that humans would be among them. The only way around this conclusion is to abandon naturalistic evolution and invoke a god supervising the process, making the right midcourse corrections to ensure that humans appeared.