How Science Responds When Creationists Criticize Evolution

Boyce Rensberger
Washington Post Staff Writer
January 8, 1997

Maybe you've encountered them, the perfectly nice people who stop you with a statement like, "Well, you know, evolution is just a theory, and it's very controversial, even among scientists."

Or maybe they say, "There's no way a bunch of gears and springs in a junk pile could suddenly fall together by accident and become a working watch. The existence of a watch tells you there had to be an intelligent watchmaker." Sometimes, they'll stump you by asserting that, on his deathbed, Charles Darwin renounced his theory of evolution.

Usually the people who say these things mean well. But the statements are based on a faulty understanding of biology. Unfortunately, many of us challenged by those who call themselves creationists are not well prepared to respond.

But science has good answers to these challenges to the theory of evolution. First, there's absolutely no controversy within science about the reality of evolution. There is a well accepted, solidly established body of evidence showing that evolution is real and, although knowledge of some mechanisms is incomplete, much is known about how evolution works. From this body of information we've drawn answers to some of the most common challenges issued by creationists.

Take that last one, about Darwin on his deathbed. Not only is it irrelevant to whether evolution is true, the statement is false. For one thing, Darwin would have had no motive to recant. Before the great naturalist died in 1882, he had the satisfaction of knowing that the Church of England and several other Christian denominations had declared there to be no conflict between his theory and the churchs' teachings. Indeed, Darwin, an evolutionist to the end, was laid to rest in the hallowed ground of Westminster Abbey.

In the generations since, most major denominations within the Christian, Jewish and Islamic traditions have found Darwinian evolution compatible with their religious beliefs. The statement by Pope John Paul II in November that evolution was more than a hypothesis was the fourth acceptance of evolution by the Roman Catholic Church.

For some people, fundamentalist Protestants most prominently, the issue likewise has been settled but with the opposite verdict.

For them, Genesis, however poetic, never uses metaphor or simile to tell the story of how the world and its inhabitants came to be. To them, the Bible is a scientific document to be taken literally. If science makes a claim counter to the Bible, creationists say it is automatically understood that science is wrong and a literal reading of the scripture is right.

Creationists believe that God created each kind of living thing independently and instantaneously about 6,000 years ago and all during the first six days.

Evolutionists believe that all living things are descended, through a cumulative series of genetic changes, from one common ancestor, or perhaps a few ancestors. The first ancestors would have been primitive, self-replicating, cell-like structures that arose more than 3.5 billion years ago. Evolutionists are, however, quite far from explaining how the first living thing arose.

Herewith are criticisms you may hear, drawn from creationists and their literature, and responses based on what scientists have learned. What follows is not an attack on creationism but a defense of evolutionism.

Evolution is just a theory; it hasn't been proved.

Well, yes, evolution is a theory, but not in the way that critics think. When scientists refer to it as the "theory of evolution," the wording does not mean that they doubt it's true. Evolution has been nailed down about as solidly as anything can be in science.

The confusion arises because in science "theory" means more than "hypothesis." A hypothesis is a speculation or a prediction. Experiments or observations are needed to verify it. A theory, on the other hand, is a broad explanation for a class of phenomena. It generally is bigger and grander than a single hypothesis, even one that has passed all tests.

Thus, atomic theory is the coherent set of explanations of the structure and behavior of atoms. Einstein's theory of relativity has passed every experimental test but still is called a theory.

In science, an explanation becomes a theory if it is internally consistent, always agrees with observations and can be used to make testable predictions (hypotheses). Within a theory may be "laws," which can be expressed more tersely, often with mathematical equations.

So, has evolution been proved true? Strictly speaking, no. It is an accepted fact of scientific logic that you can never prove something true. Experiments and observations can only falsify theories or hypotheses.

Scientists insist on many tests of a hypothesis, the results all tending in the same direction before they accept it as probably true. The more evidence, the more acceptable it is and the higher the probability of truth.

Still, in science there is no such thing as 100 percent certainty. The evidence for evolution is so overwhelming that scientists say the probability of it being true approaches 100 percent. The fact that creationists say they are fully 100 percent certain of their view is based not on scientific evidence but, as their own literature says, on their faith in the literal truth of Genesis, which gives rise to doubts about the scientific case.

In fact, evolution has massive amounts of supporting evidence from many fields of science--anatomy, geology, animal behavior, paleontology and even molecular biology.

The odds against random chance producing a complex organism from lifeless ingredients are astronomical.

If chance were the only factor, this would be true. But chance is only one of two key players, and the other, natural selection, is decidedly not random. It favors species better adapted to their environments and kills off those less suitable. The process applies to all living things.

Here's how it works. Every generation usually produces more offspring than can survive, given limited supplies of food, water, space and other resources in a given habitat. For no species are Earth's natural resources unlimited. Individuals must compete with other members of their own species for these resources.

The offspring, however, are slightly different from one another in genetic endowment. Because of mutations in genes--here's the only random part--siblings differ in various subtle ways.

As a result, individuals that happen to inherit traits that give them an advantage automatically will be more likely to survive than their relatives lacking the trait.

They probably will have more offpsring, and the offspring will inherit the genetic trait.

Far from being random, natural selection ensures that the only players in what Darwin called the "struggle for existence" are those that have passed all previous tests.

There are no transitional fossils.

The fossil record is rife with gaps where evolution says there should be intermediate forms.

Far from it. Paleontologists have found many transitional fossils representing intermediate forms in the evolution of one major form of life into another.

There are, for example, excellent skeletons of extinct animals showing the transitions from primitive fish to bony fish, from fish to amphibian (the first four-legged creatures walked on the ocean bottom, not on land), from amphibian to reptile, from reptile to mammal (it happened about the time the first dinosaurs were arising), from reptile to bird (the bird-sized Archaeopteryx specimen from southern Germany, for example, has feathers and dinosaurlike teeth) and even from land animal to whale (there are fossil whales with four legs, and modern whales still have remnants of hind legs buried in their flesh; their front legs have changed into flippers).

There is abundant fossil evidence showing transitional diversifications among mammals into rodents, bats, rabbits, carnivores, horses, elephants, manatee, deer, cows and many others. One of the most finely divided sequences of transitions documents the evolution of apelike creatures through half a dozen intermediate forms into modern humans.

Perhaps the oldest known transitional sequence involves the horse. It starts about 55 million years ago with a terrier-sized creature that had four toes in front and three in back. This is the famous species once called Eohippus, but now, for technical reasons, renamed Hyracotherium.

The lineage evolved through at least 14 steps, each represented in the fossil record by a successful species, until the modern horse, a pony-sized Equus, the genus to which modern horses belong, appeared about 4 million years ago.

Still, gaps in the fossil record will keep paleontologists busy for decades. Most kinds of fossils are extremely rare. After all, to become a fossil, the species not only must exist, but individuals also must die in places where conditions are right for preservation. In other words, the skeleton must be buried in sediments with preservative properties before scavengers or weathering can destroy it. Then only a few of those places will undergo erosion or uplifting that exposes the long-buried remains.

The fossil record shows that species do not evolve but exist for millions of years without changing.

It is true that most species appear to persist unchanged through time. Although some evolutionists once thought that continuous gradual change might be the rule, it is now clear that species are more stable.

They come into existence after relatively brief periods of rapid change in a small sub-population of a preexisting species. After only a few centuries or a few millennia of change, the new species persists with little further change for long periods, sometimes millions of years. This varying tempo is called "punctuated equilibrium."

The periods of change generally coincide with episodes of environmental instability such as sudden climate change. A desert may become a wetland; a warm climate may turn cool. The change may wipe out species not suited to the new conditions and create opportunities for new "lifestyles" to emerge.

So, if individuals happen to have inherited a mutation that "pre-adapted" them to the new regime, they automatically prosper at the expense of their brothers.

Once the environment stabilizes, so do the species in it.

Evolution has never been observed.

Yes, it has, and not just the rise of minor changes but of whole new species.

Strictly speaking, evolution is simply a change in the frequency with which specific genes occur in a population. By this token, there is the well known example of the peppered moth of Britain.

In 1848, 98 percent of these moths were gray, a color that hid them from birds when they perched on gray lichens that covered tree trunks. Darker-winged variants were rare and tended to be eaten by birds. Then as the Industrial Revolution's smokestacks killed the lichens and darkened tree trunks, the gray moths stood out and were eaten while the darker mutants survived.

Gradually, the moth became a predominantly dark-winged species and, by 1898, gray individuals were less than 5 percent of the total. Now that air pollution controls have taken effect, lichens are growing back, and the peppered moth again is becoming a chiefly gray species.

In that case, evolution by natural selection occurred but did not create a new species. Gray moths still could interbreed with black moths, proving that they belonged to the same species.

The rise of bona fide new species has, however, been documented in such laboratory-reared species as the fruit fly, of which eight new species have been found. Also, six new species of other insects have been seen to form. In such free-living species as mice, a new species has emerged on the Faeroe Islands in the last 250 years.

In recent years, scientists also have documented evolution of a new species of marine worm, called a polychate. And among plants, a least a dozen new species have been seen to arise over the last 50 years, including a new species of corn.

Natural selection cannot change one species into another because it can work only on variation already present in the species.

Yes, but new variation is being generated continuously by mutations. In the case of the peppered moth, genes for light and dark wings were present in the population, and nature merely favored one over the other. Nonetheless, the variation had to have arisen at some point in the past.

Each gene is the code telling a cell how to make a particular protein. Once made, the protein carries out specific functions that make one kind of cell different from another and, sometimes, one organism different from another. Thus mutations can change the whole organism's form and function.

Although creationists sometimes assert that all mutations are harmful, this is not so.

Mutations happen all the time, primarily as a result of simple errors in the gene-copying process that makes sperm and eggs. Not only can a tiny change be introduced into a gene, but an entire functional module from one gene can be copied and inserted into a different gene, creating in one step a protein with radically new properties. This is one way in which very large changes can occur suddenly.

Most mutations are neutral because most of the genome is noncoding DNA--the so-called "junk DNA." Most of the rest are harmful, killing the cell or perhaps the whole embryo long before birth. But the rare mutation will confer an advantage. Quite often, however, the advantage will be irrelevant in the current environment of the species.

But consider this scenario. Suppose that the world of the chicken suddenly became flooded and the hapless birds had to float on the water and paddle about. Because most chickens don't have much webbing between their toes, they wouldn't move very fast. But if one odd chicken happened to be born with a little webbing between its toes, a trait perhaps disadvantageous on land, it could paddle faster and maybe escape predators more easily. Obviously, this chicken would be more likely to survive and to raise a family of web-toed chicks.

Life contains structures and systems too complex to have evolved graduallly, step by step.

This is one of the oldest criticisms made by creationists, and recently it has been revived. Darwin himself anticipated it, citing the eye with all its "inimitable contrivances" as a structure that may seem too complex to have arisen through a series of steps, each conferring sufficient advantage that it would be favored for survival.

Darwin said that, if it could be demonstrated that any structure exists in nature that could not have arisen by natural selection, "my theory would absolutely break down."

Since then, biologists have vindicated Darwin by discovering many examples of primitive eyes among various species, ranging from the simplest eye spots of a few light-sensitive cells through progressively more complex forms to the complete, highly sophisticated mammalian eye.

Together, these discoveries show how a series of many cumulative steps could create a human eye. In fact, biologists now know that eyes arose and evolved independently at least 40 times.

Last year, Michael Behe, a biochemist, published Darwin's Black Box, raising the argument again. Within science it was widely dismissed for its tactic of argument from ignorance.

Behe essentially contends that if you can't imagine how something could have happened naturally, then that is proof that the thing must have happened supernaturally. In science, ignorance is no more evidence than was Darwin's astonishment about the eye.

Behe cites several structures and processes, some inside cells and some involving whole organ systems, that he says are "irreducibly complex" and therefore must have arisen by special creation, by God creating the whole thing at one stroke.

One, for example, is a series of at least seven chemical reactions that must occur within blood for it to clot and stop a wound from bleeding. In this scientifically well-known "cascade" of reactions, substance A first acts on substance B, changing it into a form that can act on substance C, which then is changed so it can act on substance D and so on. Obviously, the system works well.

Behe argues, however, that it is inconceivable that the cascade could have evolved from some simpler form with fewer steps because all steps now are essential. Since each step requires the participation of several components, Behe writes, not only is the entire blood-clotting system irreducibly complex, but so is each step in the cascade.

As it happens, scientists have deduced the nature of an evolutionary path that a primitive blood-clotting mechanism could have followed to evolve the more complex cascade. The process is biologically plausible and uses well-known mechanisms that exist in all cells for duplication and modification of existing genes followed by inactivation of the old gene.

The mutations required at the beginning of the process are neither beneficial nor deleterious, but once they occur, they produce a blood-clotting system that can be controlled more precisely. This is beneficial since a runaway blood-clotting mechanism could turn the entire bloodstream into one massive clot.

The same events that turn a one-step process into a two-step process could be repeated indefinitely, scientists have found, adding still finer control at each step, conferring yet greater advantage.

The fact that this problem has been addressed, incidentally, refutes one of Behe's contentions. He says evolutionists never try to explain how complex systems might have arisen through incremental changes. In fact, scientific literature includes numerous such instances.

Evolution violates the Second Law of Thermodynamics.

A complete answer would require lots of mathematics and a deeper understanding of the Second Law than can be described here. The short answer, however, is: no, it doesn't.

The Second Law can be stated in many different ways, but the most relevant is that order cannot emerge from disorder in a closed system. In other words, a random jumble cannot spontaneously assemble itself into some orderly structure without tapping some outside energy source. Some creationists say this means that life cannot evolve from simple to complex. Complex life forms would have to have been created separately.

Earth, however, is not a closed system. It receives huge amounts of energy from the sun and from chemical bonds within compounds, and this energy allows life to evolve.

If the Second Law truly prohibited local emergence of increased order, there would be no ice cubes. The greater orderliness of water molecules in ice crystals than in the liquid state is purchased with the expenditure of energy at the generator that made the electricity to run the freezer. And that makes it legal under the Second Law.

Creation science is genuine science.

The philosophical underpinnings of creation science automatically place it in a very different realm from natural science. The natural sciences (biology, chemistry, physics and the like) begin with the assumption that nothing should be accepted as true for purposes of research unless it can be demonstrated reliably through observation or experiment.

Creation science starts with the assumption that Genesis is literally true. "God's inerrant word," as recorded in the Bible, "must always prevail" over anything that natural science says, according to Henry M. Morris, founder and recently retired director of the country's largest and most influential creationist organization, the Institute for Creation Research in El Cajon, California.

The institute's literature describes the institute as "a Christ-focused creation ministry."