Darwin's theory of evolution by natural selection is the only scientific explanation for the spectacular diversity of life on Earth. It provides a powerful framework for understanding nature and is one of the essential theories at the very core of science.
Yet from the moment it was first published, Darwin's theory of evolution has been engulfed in controversies, some of which persist to this day. Indeed the current controversy is strongly rooted in the objections first expressed 150 years ago. As Darwin himself anticipated, some people have held to the conviction that species are the result of special creation through the action of a Creator. Some find incompatible with their religious beliefs the concept that humans share a common ancestry with earlier primates, and that humans and other species evolved over immense spans of time.
Others see the process of evolution itself as one of the qualities of a universe created by a God. Some also embrace the notion, as expressed for example in a statement by Pope John Paul II, that evolution may be a valid scientific explanation for the origins of body form and other aspects of the material world, but that God alone is responsible for the origin of the human soul.
Certain expressions of Creationism--for example, the view known as Intelligent Design--hold that Darwinian evolution is not sufficient to explain the origins of complex structures, such as the eye, or complex organisms, such as humans. They assert that such innovations must be the act of an Intelligent Designer.
Creationism, including Intelligent Design, does not offer a scientific alternative to the theory of evolution. By invoking the act of a Creator or an Intelligent Designer as the explanation for life's diversity, Creationism invokes a cause that lies outside our powers of observation and thus outside the realm of scientific inquiry.
Many people, including prominent religious leaders and scientists, view the search for understanding as one that embraces both scientific explorations into the material world and a spiritual search for the meaning of human existence, with no inherent conflict between the two.
Social controversy over Darwin's theory is long-standing and will doubtless persist. Yet, objections to the theory based on spiritual or philosophical perspectives do not undermine its scientific validity, importance, and impact. For 150 years since the publication of Darwin's Origins of Species, the theory of evolution by natural selection has not been seriously challenged by any other scientific explanation. Evolution serves as the foundation for all of modern biology, including research critical to human welfare, medicine, and the fight against disease.