Charles Darwin's theory of evolution is the foundation of modern biology, with implications for virtually every aspect of science, yet the theory often sparks fierce cultural debate. In the United States, for example, the phrase "Teach the Controversy" is widely used in discussing how evolution should be taught in the public schools. What is this theory, and why is it so controversial?
The most cursory examination reveals that from a scientific perspective there is no controversy at all; virtually all major scientific organizations across the world accept that the evidence for evolution is incontrovertible (Interacademy Panel on International Issues). Instead, the controversy arises when people conflate the science of evolution with their religious beliefs. This is not to say that science must be kept totally distinct from religion; on the contrary, there can and should be constructive dialogue between the two. However, to evaluate a scientific theory, the rules of science must be applied, as they are applied to all scientific disciplines. The purpose of this article is to explain what evolution is, to describe some of the overwhelming evidence that supports it, and to explain why one of the proposed alternatives to evolution, "intelligent design," fails to qualify as science. I will also briefly address why evolution has been perceived as a threat to religion and provide some references that challenge this perception.
The Basics of Evolution
Some of the most compelling evidence for evolution has come through discoveries in the field of genetics.
At the most basic level, evolution refers to the fact that species change over time. By this we don't mean that individual members of a species change, although this is certainly true. Rather, if one considers all of the individuals within a given species, one notes that there are changes from generation to generation. Biologists usually describe this change in terms of genes; we say that over time, the genetic structure of a population changes. This refers to the fact that the frequency of each gene within a population can change from generation to generation. These genetic changes are often, but not always, apparent in the physical appearance of organisms as well.
Evidence for evolution is all around us. For example, strains of certain bacteria, such as those causing tuberculosis, have become increasingly resistant to antibiotics. This resistance is the result of genetic variations that were originally absent or rare but that have become increasingly common. Furthermore, humans have been using the processes of evolution to their advantage for millennia. Our selective breeding of plants and animals for desirable characteristics has produced strains that scarcely resemble the original organisms. Thus, although the term evolution is associated with controversy, evolution itself is quite a straightforward and familiar phenomenon.
What is not so obvious is how and why evolution takes place. During the golden age of Islam, a number of Muslim scholars recognized evolutionary processes in nature (T.O. Shanavas). In Europe, however, up until the 18th and 19th centuries, it was widely held that living organisms did not change at all but had been created by God just as they appeared. It was also believed that all species that had ever existed still existed; in other words, there was no concept of extinction. However, in Europe and around the world, an increase in scientific exploration led to the discovery of fossils that did not resemble any known living forms or that were very different from present forms. These and other discoveries led some scientists and philosophers to accept the idea of evolution and to postulate how it might occur. Among these scientists was Charles Darwin.
The Origins of the Theory of Evolution
Contrary to popular belief, the contribution of Charles Darwin was not to note that evolution occurs, although he certainly helped to spread acceptance of the idea. Rather, Darwin was the first to recognize and describe how and why evolution takes place. Darwin developed his ideas about evolution through close observations of the natural world. The most important of these observations came during a trip to the Galapagos Islands that he made while serving aboard the HMS Beagle. There he noted that each island had its own array of animals that differed from its neighbors. He began to think that these differences were determined by the different natural conditions on each island.
After his trip, Darwin read a book by a clergyman named Thomas Malthus, who observed that organisms generally produce more offspring than can be supported by available resources and that this excess leads to competition. Putting this idea together with his own observations, Darwin was able to formulate a hypothesis. He suggested that there is variation among the individuals of a given species and that some individuals are better suited or adapted to their natural environment than others. Those that are better adapted are more successful — on average they live longer and have more offspring. Furthermore, specific adaptive characteristics can be passed on to their offspring. Over time, individuals possessing the more adaptive characteristics increase in number relative to those without them and populations change accordingly. For example, if it is advantageous for an animal to be small in a given environment — perhaps to better hide from predators, or to survive on a more limited diet — and size is a hereditary trait, then smaller individuals will have an advantage and produce more offspring that are also small. Over time, the population as a whole will become smaller. Darwin called this concept natural selection, and it is this concept to which the phrase the theory of evolution generally refers.
Many theologians believe that intelligent design is not only "bad science" but also "bad theology."
Darwin's ideas explain changes within individual species, but they also have broader implications. With natural selection as a framework, it becomes possible to explain the vast diversity of life on earth through natural causes. Starting with a common ancestor, populations arose and, through natural selection, diverged into distinct species. Some of these species disappeared, while others persisted and themselves diverged, until gradually the staggering array of species that exist on earth was produced. This explanation suggests that all organisms on earth are related through a common ancestor, and is encompassed by Darwin's own phrase "descent with modification."
What evidence is there for natural selection as the mechanism for evolution, and for the idea that all of life arose from a common ancestor? A widespread misconception is that there is little or no evidence for these ideas, but in fact the very opposite is true. One of the most fascinating and powerful aspects of evolutionary theory is the fact that the more knowledge we gain, the more support we find for the theory even in disciplines about which Darwin knew nothing, such as genetics.
The Nature of Science
The Tiktaalik is a fish with limb-like fins and appears to represent the transition between fishes and land animals.
Before describing this evidence, it is important to understand what makes an idea or an observation "science" and what distinguishes science from other realms. At its most fundamental level, science is based on the idea that the world is understandable and predictable and that, through inquiry and observation, natural explanations can be found for natural events. Science is thus a process through which people seek to understand the world. Science is restricted to natural explanations because, over time, that has proved to be the most productive framework in which to work. If supernatural explanations were permitted, the answers to difficult questions might never have been found. For example, mental illness was once thought to result from contact with the supernatural but we now understand the biochemical underpinnings of behavior. Furthermore, while supernatural activity may occur, it is by definition not predictable and is thus outside the realm of science.
Science depends on evidence, or facts obtained through observation or experiment, and scientists strive both to explain evidence that has already been obtained and to predict evidence that has not yet been found. These explanations are called theories and are the highest level of scientific knowledge. The definition of theory in science is very different from that in common usage, where the term refers to a guess, or a hunch, as opposed to a fact. In science, a theory is an overarching explanation for a set of facts, and a theory does not become a fact.
Understanding the nature of science allows us to appreciate why the evidence for evolution is so convincing. For example, the idea that all organisms arose from a common ancestor suggests that there must have been "transitional" species that had characteristics of both older and newer species. These transitional species may no longer exist, but evidence of them should be apparent in the fossil record. In Darwin's time, few fossils of transitional species existed but since then many have been found. Perhaps the most famous is Archaeopteryx, which was first discovered in 1861. Archaeopteryx has both avian and reptilian features and provides strong evidence of the transition from dinosaurs to birds. Others include Protoarchaeopteryx and Caudipteryx, feathered dinosaurs that further illustrate the link between dinosaurs and birds. The most recent discovery, called Tiktaalik, was a fish with limb-like fins and appears to represent the transition between fishes and land animals. These fossils offer compelling evidence for evolutionary theory because their existence was predicted before they were actually found; this predictive capacity is one reason why evolution is one of the most powerful theories in science.
Darwin and the Galapagos Islands
Darwin's sketches of the Galapagos finches from his journal highlight the different beaks.
Further evidence for the theory of evolution comes from real-time observations of how species change in response to changing environmental conditions. A study of "Darwin's finches" has provided unique insights to how this occurs. Darwin himself was fascinated by these Galapagos Island birds whose beaks differ significantly from island to island. He speculated that varying conditions on each island caused a single original species to diverge into many species but was unable to collect evidence to support his hypothesis.
Many years later, Peter and Rosemary Grant documented that beaks tend to get thicker in times of drought and that the change is measurable over just a few generations. Larger beaks enable the birds to feed off seeds that are more abundant during drought, and birds with larger beaks have higher survival and reproduction during drought. When drought conditions abate, beak sizes shrink as finches take advantage of an increase in seeds that are smaller and easier to open. The Grants have also demonstrated that the introduction of new finches to a given habitat can lead to rapid divergence in beak size between the introduced and original populations. Thus, research has demonstrated that beak size responds to an array of environmental pressures and suggests how beak variation among the 13 different finch species in the Galapagos arose. Furthermore, while the actual formation of new species is too slow to observe directly, it is precisely these kinds of changes that cause speciation to occur.
Some of the most compelling evidence for evolution has come through discoveries in the field of genetics. When Darwin first proposed his theory, the existence of genes was unknown. Although his theory depended on the idea that traits were passed down from parent to offspring, he had no idea how that occurred. As it became clear that genes are the mechanisms of inheritance, it was initially thought that these ideas would replace Darwin's theory. Instead, they provided further confirmation that his theory was correct. For example, if, as Darwin suggested, all creatures on earth are related through a common ancestor, then all species should share at least some of their genetic material. This has proved to be resoundingly true. Animals can share as much as 20 percent of their genetic material with plants, and many mammals share more than 90 percent of their genetic material. Genetics has also demonstrated how variation in a population of individuals occurs. As genetic information is transcribed, "mistakes" can be made. These mistakes are called mutations. Mutations are usually harmful to organisms but occasionally they make an individual better adapted to its environment. In these cases, natural selection causes them to spread through populations. Darwin's theory of evolution has thus merged with the field of genetics into what is called the modern synthesis.
In science, a theory is an overarching explanation for a set of facts, and a theory does not become a fact.
These three examples represent just a tiny fraction of the accumulated evidence for evolution. In spite of all this evidence, however, an alternative theory has recently been proposed. This is called intelligent design, and it argues that there are some features of the natural world that are too complex to have arisen through natural selection alone. This position is not the first challenge to some aspect of evolution. A number of scientists argue, for example, that natural selection is not a slow, gradual process as Darwin believed, but rather one that takes place in fits and starts mirroring major climactic and geological activity.
However, proponents of intelligent design do not propose another natural process as an alternative to natural selection to explain the occurrence of complex features. Instead, they argue that such features must be the product of an "intelligent designer." This designer is not named, but is understood to be a supernatural being, and most of the theory's proponents admit that they are referring to the God of their particular faith. But because science excludes the supernatural by definition, intelligent design cannot be called science. Rather, it is a philosophical or religious position. It is worth noting, however, that many theologians believe that intelligent design is not only "bad science" but also "bad theology." This is because those features of the natural world that might appear to be "irreducibly complex" and thus proof of the activity of a supernatural designer are likely to be one day understood solely through natural explanations. Are we then to assume that we have disproved God's existence? Of course not. And yet, if one looks for God in the gaps in scientific knowledge, that God must become more limited as more and more scientific gaps are filled.
Science and Religion
Intelligent design is appealing to many people because it challenges the mistaken view held by some scientists that science explains everything and provides justification for an atheistic world view. Unfortunately, a number of atheistic scientists are extremely vocal in arguing this position, but their argument is every bit as unscientific as intelligent design. Science has nothing to say about the supernatural; it can neither prove nor disprove its existence. Nonetheless, the perception that science promotes an atheistic and materialist point of view has led many people to believe that they must choose between science and religion. Intelligent design would seem to provide an alternative to this stark choice, but it does so at the expense of both science and theology.
Fortunately, a number of theologians and religious scientists have addressed this false dichotomy and described ways of reconciling the two while compromising neither. Among these are Kenneth Miller, a Catholic biologist; Francis Collins, the director of the Human Genome Project and an evangelical Christian; and John Haught, a Catholic theologian.
I would also like to recommend a publication of the American Association for the Advancement of Science's Program of Dialogue on Science, Ethics, and Religion. This book, called The Evolution Dialogues: Science, Christianity and the Quest for Understanding, demonstrates that science and religion need not conflict. It also describes the many ways that people have found to reconcile the science of evolution with their religious beliefs. T.O. Shanavas (Vice President of the Islamic Research Foundation International, Inc. located in Louisville, KY) has written a brief but informative review on the relationship between Islam and science with specific attention to evolution. And finally, for a personal Muslim perspective on the relationship between science and religion, one needs look no further than the illuminating interview with Bruno Abd-al-Haqq Guiderdoni here on IslamOnline.net. Dr. Guiderdoni suggests that the beauty and truth of the Qur'an are beyond question, so there is no need to "prove" or make a science of the Qur'an. Furthermore, the study of science is a way of learning from God and glorifying God and should not be a threat to religious beliefs.