Ever since evolutionary thought began, there have been dissenters who have grappled with the fact that evolution is inconsistent with religious accounts of creation. In recent years, dissenters in North America have pushed so called "intelligent design" as a scientific alternative to evolution, and have advocated for intelligent design to be taught alongside evolution in American science classrooms. Let's take a closer look at this controversy.
Intelligent design is based on the notion that some aspects of the natural world are better explained by an intelligent, supernatural designer, rather than by evolutionary processes. Intelligent design rests on two assumptions: 1) that a supernatural being can work outside the laws of science and nature, and can interfere with natural events and that 2) some natural phenomena are "irreducibly complex". That is, they could not have arisen by gradual evolutionary processes because in simpler, more preliminary forms, these structures would have been non-functional and/or would have conveyed no survival advantage.
The scientific community overwhelmingly rejects intelligent design as a viable alternative to evolution for several reasons. First of all, many of the central claims of intelligent design—such as the argument for irreducible complexity—have been repeatedly dispelled. For example, the bacterial flagellum has often been cited as an example of an irreducibly complex structure. The flagellum is a tail-like projection that helps bacteria to move, and is made of several different protein building blocks. Proponents of intelligent design have argued that removing any of these proteins would result in a non-functional flagellum. However, recent evidence suggests that the flagellum is not irreducibly complex at all—in fact, some of the proteins making up the flagellum serve other purposes, helping bacteria to inject toxins into other cells. Thus, although having a "piece" of a flagellum doesn't help the bacterium move, it does serve another important function, and therefore could have been favored by natural selection.
The second reason scientists reject intelligent design as an alternative to evolution is because intelligent design is fundamentally non-scientific. Science as a process requires formation and revision of hypotheses, experimentation, collection of data and observations, and inferences based on observed evidence. Claims made by proponents of intelligent design are neither testable nor falsifiable, because there is no way to empirically test for the presence of a supernatural being.
The debate on whether intelligent design should be taught in schools arises frequently in the news. A relatively recent case—Kitzmiller vs. Dover—went to trial in 2005 in Pennsylvania. Several parents with children in public schools sued the Dover, Pennsylvania school district because the school board had mandated that intelligent design be taught alongside evolution. After hearing testimony from both sides, the judge ruled that teaching intelligent design was akin to teaching creationism, and was unconstitutional. You can read more about the Kitzmiller vs. Dover case here.
This issue will undoubtedly remain controversial in the years to come, but it's important to recognize that this debate is not a culture war between religion and science. The United States Constitution protects everyone's right to religious freedom. Rather, the issue here is 1) whether intelligent design should be taught in science class, since it is neither testable nor falsifiable and 2) whether teaching intelligent design in public schools violates separation of church and state, or unfairly promotes one religion over others.