The theory of evolution is the foundation of modern paleontology and biology. It provides a coherent scientific explanation of the incredible diversity of life on Earth - an explanation which is understandable within human experience. Evolution allows us to understand the physical similarities between the saber-toothed cat and the family cat. It explains why we find hip bones in living whales, which have no hind legs, and ear muscles in humans, who cannot use them to rotate their ears. Evolution provides a scientific explanation for why animals that swim tend to be streamlined and why aggressive carnivores have large brains and excellent eyes. It explains why all DNA, whether taken from yeasts, or oaks, or clams, or human beings, is made of the same four chemical bases. At the same time, evolution increases our understanding of issues of major importance to society including overpopulation, the emergence of virulent new diseases, the use of agri- cultural pesticides, and genetic engineering - to name a few.
In science, we do not use the term "theory" lightly. Statements such as "evolution is just a theory" show a lack of understanding of both the term 'theory' itself and the very nature of science and how it is done. Evolution is as well-supported by evidence as the theory of gravity or the heliocentric theory of our solar system. The data supporting evolution are vast, having been gathered over hundreds of years and from many disciplines of science.
There are many, many fascinating questions still to be answered, and even more questions yet to be asked. As we continue to learn more about life on Earth, the theory of evolution itself continues to evolve. That is the strength and excitement of doing science - learning how the Universe works.