When the name Charles Darwin is uttered, an immediate association brings about the concept of Evolution. Although he was not the first to discover this phenomenon, he was the first to explain it. In his book, The Origin of Species, Darwin discusses evolution- through variation, why it occurs, the struggle for existence, natural selection, the geological record, and several other topics. This book brought him great recognition as well as many violent attacks. It was written in a time in history when the people were very strong believers in the Church and God. Darwin was the first to contradict their religious beliefs of Creation, and was pummeled with criticism. Although today some still disagree, his explanation of evolution through natural selection is accepted by many. Darwin was just twenty-three when he began his journey aboard the H.M.S. Beagle. He traveled to South America and collected, observed, and noted everything he saw. During his travels, he found fossils of animals that looked like living animals, but were larger, different, and no longer on Earth. How could this be? According to Genesis, no plants or animals had changed since God had created them. If everything was exactly the same as it had always been, then how could extinction occur? Although this discovery went against the Church, Darwin could not ignore it. The more he observed, the more evidence he found; the Earth must have slowly and gradually changed since Creation, giving plants and animals time to adapt to the changes. He had just described evolution. Variation Within Species Over time Darwin observed many more clues that helped him somewhat understand the reasoning behind evolution. The Origin of Species begins with a discussion on variation. Darwin reflects on the diversity of older, cultivated species; they seem to differ much more than those in nature. He gives several examples of variation to illustrate this concept.