Ebook: Science, Evolution, and Creationism

We are most fortunate that our nation's scientists and medical doctors, through their professional organizations, the National Academy of Sciences and the Institute of Medicine, have provided us with this succinct, comprehensive and authoritative account of evolution and its creationist critics.

I do not wish to rehash any of the points made by the other reviewers. However there is one excerpt from the book's FAQ section, which is an excellent answer to the question "How can random biological changes lead to more adapted organisms?" I quote it here in the hope that it gives some young person a taste of science:

Contrary to a widespread public impression, biological evolution is not random, even though the biological changes that provide the raw material for evolution are not directed toward predetermined, specific goals. When DNA is being copied, mistakes in the copying process generate novel DNA sequences. These new sequences act as evolutionary "experiments." Most mutations do not change traits or fitness. But some mutations give organisms traits that enhance their ability to survive and reproduce, while other mutations reduce the reproductive fitness of an organism.
The process by which organisms with advantageous variations have greater reproductive success than other organisms with a population is known as "natural selection." Over multiple generations, some populations of organisms subjected to natural selection may change in ways that make them better able to survive and reproduce in a given environment. Others may be unable to adapt to a changing environment and will become extinct.