Creationism is the belief that species originated separately and remain fixed. Most versions of creationism are religiously inspired and suggest that the origin of species is by supernatural action.
Powerful reasons why evolutionary biologists do not take creationism seriously:
• Creationism offers no explanation for adaptation. Living things are well designed, in innumerable respects, for life in their natural environments. If the adaptation of organisms is attributed to the genius of God it just pushes the problem back one stage. Without a theory of adaptation, as Darwin realized, any theory of the origin of living things is a non-starter.
• Biological classification: if species had independent origins, we should not expect that, when several different and functionally unrelated characters were used to classify them, all the characters would produce strikingly similar classifications.
• The fossil record of the faunas and floras of the past differ so much from those of today, both in what species were present and what were not, that all the species that have ever lived could not have been created at the same time. We should expect to find at least some modern species in the deep past if there had been a simultaneous mass creation.
Outside of science, creationism is still an emotive issue: however, it is worth pointing out that there need be no conflict between the theory of evolution and religious belief: accepting evolution does not mean rejecting religion and they should be able to coexist peacefully in anyone's set of beliefs about life. Indeed as Richard Dawkins points out, many practicing evolutionary biologists hold some form of religious belief.